opinionated-telemetry

We've thought a lot about Telemetry in Node.js, so you don't have to

Opinionated OpenTelemetry patterns extracted from years of learnings from real-world o11y, to help Node.js projects eveywhere. Sensible defaults, tools, and hooks to cut out the noise and cost from default "instrument everything" implementations, and really drill down and understand what's most important.

The defaults included may or may not be right for you, so be sure to read the options carefully. Comes with powerful hooks for sampling spans, dropping spans, collapsing intermediate spans, globally "auto-instrumenting" important bits of your own code, as well as some nice helpers for some libraries I've used in the past.

Contributions & feedback are welcome, especially if you have ideas or other libraries with sensible default hooks that you'd like to share.

Best suited for & meant use with Honeycomb.io. Virtually unlimited attributes on a span for no additional cost is so powerful, I can't believe I don't hear its praises more often.

Features

• Stuck span detection: detects in-flight spans exceeding a threshold and exports early "diagnostic" span snapshots, so you can understand what might be broken sooner (long queries, hung requests, etc.)
• Sync span dropping: automatically drops non-root "synchronous" spans that start and end in the same tick by default (root spans are always kept). Configurable to allow for keeping specific spans e.g. keeping sync spans > 100ms, or spans with a certain name, etc.
• Span collapsing: allows us to drop intermediate spans (e.g. knex, graphql) and merge their attributes into child spans. No use having both a knex span that has a single nested pg or mysql span underneath, unless there is an error in the knex span or something
• Conditional span dropping: tail-based conditional dropping with child buffering — register a shouldDrop callback at span start, evaluate at span end based on duration/error/attributes, with automatic child reparenting. Supports both simple drop (no attribute inheritance) and collapse mode (inherit attributes into children)
• Baggage propagation: propagates baggage entries as span attributes on all child spans by default, with outbound baggage suppressed to prevent leaking sensitive data to external APIs (opt-in allowlisting by host and key)
• Memory & Memory delta tracking: captures RSS (or detailed heap, configurable) memory & memory deltas on root spans.
• Auto-instrumentation: opt-in hooks wraps exported async functions from your own codebase with auto-spans based on the function or method name, configured via ESM or Module._load patching
• Head & Tail Based Sampling: Includes sensible approaches to dealing with Head & Tail based sampling out of the box
• Burst Protection: Along with the sampling, includes some conventions for preventing a simple coding mistake that generates an infinite loop spawning thousands of spans per second from doing too much damage.
• Span aggregation: collapses N parallel sibling spans with the same name (dataloader batches, S3 multi-get, parallel DB queries) into a single aggregate span with summary statistics, while preserving individual error spans. Configurable via per-scope options or a root-level predicate, with optional custom attribute stats (min, max, avg, median, uniq, etc.)
• Flat metric exporter: opt-in exporter that wraps your metric exporter to fold dimensional attributes into metric names and expand histograms into summary stats + percentiles — so Honeycomb merges everything into a single wide event per collection cycle.
• Node runtime metrics: focused runtime health metrics (event loop delay, heap, GC, CPU, handles, memory) using built-in Node.js APIs — replaces noisy @opentelemetry/host-metrics and instrumentation-runtime-node with 18 actionable gauges and zero attributes.
• Metric filtering: drop/allow metrics by name using glob patterns, regex, or predicates — cut metric noise and cost without learning the OTel Views API
• Integration helpers: knex, graphql, bull, socket.io, express
• Event loop utilization: captures event loop utilization (0-1) on all spans. Useful for alerting on situation where expensive spans are blocking the event loop. Particularly useful when dealing with things that are synchronous, like fs calls or better-sqlite3 queries

Install

npm install opinionated-telemetry

Quick start

import { opinionatedTelemetryInit } from 'opinionated-telemetry'
import { OTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-proto'
import { HttpInstrumentation } from '@opentelemetry/instrumentation-http'
import { KnexInstrumentation } from '@opentelemetry/instrumentation-knex'

const { sdk, getTracer, shutdown } = opinionatedTelemetryInit({
  serviceName: 'my-service',
  traceExporter: new OTLPTraceExporter({
    url: 'https://api.honeycomb.io:443/v1/traces', // or wherever you want these to go. We recommend Honeycomb
    headers: '...your headers...',
  }),
  instrumentations: [
    new HttpInstrumentation(),
    new KnexInstrumentation({ maxQueryLength: 10000 }),
  ],
  // Per-instrumentation hooks, keyed by instrumentation scope name
  instrumentationHooks: {
    '@opentelemetry/instrumentation-knex': {
      collapse: true,
    },
  },
})

Core API

opinionatedTelemetryInit(config)

Initializes the OTel SDK with opinionated defaults.

opinionatedTelemetryInit({
  serviceName: string,
  resourceAttributes?: Record<string, AttributeValue>,
  traceExporter?: SpanExporter,
  metricReaders?: MetricReader[],
  resourceDetectors?: ResourceDetector[],
  autoDetectResources?: boolean,
  idGenerator?: IdGenerator,
  spanLimits?: SpanLimits,
  dropSyncSpans?: true | ((span) => boolean),        // default: true (root spans always kept)
  baggageToAttributes?: boolean,                     // default: true
  memory?: boolean | MemoryConfig,              // default: true (rss only)
  memoryDelta?: boolean | MemoryConfig,              // default: true (rss only)
  eventLoopUtilization?: boolean | 'root',           // default: true (all spans)
  stuckSpanDetection?: boolean | StuckSpanConfig,    // default: true
  onSpanAfterShutdown?: (span) => void,              // default: logger.warn
  shutdownSignal?: string | null,                    // default: 'SIGTERM'
  aggregateSpan?: (span) => boolean | AggregateConfig, // default: undefined
  onDroppedSpan?: (span, reason, durationMs?) => void, // called on dropped/sampled/stuck spans
  onCapturedSpan?: (span, durationMs) => void,         // called on accepted/exported spans
  instrumentations: Instrumentation[],
  instrumentationHooks?: Record<string, OpinionatedOptions>,
  globalHooks?: GlobalHooks,                         // hooks for all spans
  additionalSpanProcessors?: SpanProcessor[],
  batchProcessorConfig?: BufferConfig | false,    // false disables batching
  baggagePropagation?: BaggagePropagationConfig, // default: suppress all outbound
  runtimeMetrics?: NodeRuntimeMetricsConfig | false, // default: enabled
  processorMetrics?: boolean,                    // default: true — see docs/PROCESSOR_METRICS.md
  metricExporter?: PushMetricExporter,           // shorthand: we create the MetricReader for you
  metricExportInterval?: number,                 // default: 60_000 (used with metricExporter)
  metricFilter?: { drop?: MetricPattern[], allow?: MetricPattern[] }, // see Metric Filtering
  logger?: OpinionatedLogger,                    // default: console
})

Returns { sdk, getTracer, shutdown }.

memory

Captures memory usage root spans under opin_tel.memory.* attribute.

Set to true (default) for RSS-only via the fast process.memoryUsage.rss() path, or pass a MemoryConfig object to pick specific fields (rss, heapTotal, heapUsed, external, arrayBuffers) which uses the full process.memoryUsage() call. Set to false to disable.

memoryDelta

Captures memory usage deltas on root spans under opin_tel.memory_delta.* attribute.

Set to true (default) for RSS-only via the fast process.memoryUsage.rss() path, or pass a MemoryConfig object to pick specific fields (rss, heapTotal, heapUsed, external, arrayBuffers) which uses the full process.memoryUsage() call. Set to false to disable.

eventLoopUtilization

Captures event loop utilization (0-1 ratio) via performance.eventLoopUtilization(). The opin_tel.event_loop.utilization attribute tells you how saturated the event loop was during the span's lifetime. Set to true (default) for all spans, 'root' for root spans only, or false to disable.

stuckSpanDetection

Detects spans that remain in-flight longer than a threshold and exports diagnostic snapshots. Enabled by default (60s threshold, 5s check interval). Pass a StuckSpanConfig object to customize:

stuckSpanDetection: {
  thresholdMs: 60_000,   // how long before a span is "stuck"
  intervalMs: 5_000,     // how often to check
  onStuckSpan: (span, durationMs, reportedCount) => {
    // Called on every report (not just first detection).
    // reportedCount is 0 on first detection, 1 on second, etc.
    //
    // Return values:
    //   void / true  — export snapshot, keep tracking (default)
    //   false        — skip snapshot, keep tracking
    //   'evict'      — export snapshot, then remove span from all tracking
    //   'drop'       — remove span from all tracking WITHOUT exporting snapshot

    // Example: evict after 3 reports to prevent memory leaks
    if (reportedCount >= 2) return 'evict'
  },
}

Stuck span snapshots are exported with the original span's trace ID, a unique snapshot span ID (to avoid backend deduplication), an (incomplete) name suffix, and attributes:

| Attribute | Description | | ------------------------------- | ----------------------------------------------------- | | opin_tel.stuck.duration_ms | How long the span has been in-flight | | opin_tel.stuck.is_snapshot | true on snapshots, false on the real span | | opin_tel.stuck.reported_count | Number of times this span has been reported (1-based) | | opin_tel.stuck.source_span_id | The original span's ID (links snapshot to source) |

Snapshots also receive memory delta, ELU, and instrumentation hook enrichment. Re-reports are throttled — after first detection, the next report waits a full thresholdMs from the last report time.

Eviction ('evict' / 'drop'): Removes the span from all internal tracking (_allSpans, _activeSpanIds, _reportedStuckSpans, collapse state, conditional drop buffers). This prevents memory leaks from spans whose .end() is never called. If the span later has .end() called, it flows through the normal export path (the eviction is a no-op for cleanup). 'drop' also fires onDroppedSpan with reason 'stuck'.

Interaction with collapse and shouldDrop: If a span is marked for collapse or has a shouldDrop callback, but is detected as stuck, the stuck status takes precedence — the span is exported as a snapshot. When the real span finally ends, it's exported with opin_tel.stuck.is_snapshot = false to indicate it was previously reported as stuck.

batchProcessorConfig

Overrides for the internal BatchSpanProcessor. Opinionated defaults differ from OTel's out-of-the-box values:

| Option | OTel Default | Opinionated Default | | ---------------------- | ------------ | ------------------- | | scheduledDelayMillis | 5000 | 2000 | | exportTimeoutMillis | 30000 | 10000 | | maxExportBatchSize | 512 | 512 | | maxQueueSize | 2048 | 2048 |

Pass a BufferConfig object to override any of these:

opinionatedTelemetryInit({
  batchProcessorConfig: {
    scheduledDelayMillis: 1000, // flush every second
    maxQueueSize: 4096,
  },
})

Set to false to disable batching entirely and use a SimpleSpanProcessor instead. Spans will be exported immediately as they complete, which is useful for development, testing, or low-volume services:

opinionatedTelemetryInit({
  batchProcessorConfig: false,
})

baggagePropagation

By default, OpenTelemetry's W3CBaggagePropagator injects all baggage entries into a baggage HTTP header on every outgoing request — including requests to third-party APIs. This means any data you set as baggage (request headers, user IDs, tokens) can silently leak to external services.

opinionated-telemetry ships a FilteredBaggagePropagator that suppresses all outbound baggage by default. Inbound baggage extraction always works — this only affects what gets sent on outgoing requests.

To allow baggage propagation to specific internal services:

opinionatedTelemetryInit({
  // ...
  baggagePropagation: {
    // Only propagate baggage to these hosts
    allowedHosts: [
      '*.internal.example.com', // wildcard subdomain match
      'partner-api.trusted.com', // exact match
    ],
    // Only propagate these baggage keys (required — omit or [] to block all)
    allowedKeys: [
      'requestId',
      'app.*', // wildcard prefix match
      // '*',   // uncomment to allow all keys
    ],
  },
})

| Option | Description | | -------------- | ---------------------------------------------------------------------------------------------------------------------------- | | allowedHosts | Host patterns where baggage is propagated. Supports exact match and *.domain.com wildcards. Default: [] (suppress all) | | allowedKeys | Baggage key patterns to include. Supports exact match, prefix.* wildcards, and * for all keys. Default: [] (block all) |

How host matching works: The propagator reads server.address from the active client span (set by instrumentation-http before injection). If there's no active span or no server.address attribute, baggage is suppressed (safe fallback).

Note: If the OTEL_PROPAGATORS environment variable is set, NodeSDK ignores the filtered propagator and uses the env-configured propagators instead. A warning is logged when this happens.

The FilteredBaggagePropagator class is also exported for standalone use if you need to configure propagators manually.

Span Aggregation

When a parent span fires off many parallel child spans with the same name (dataloader batches, S3 multi-get, parallel DB queries), the result is N nearly-identical sibling spans that add volume without proportional signal. Span aggregation collapses them into a single aggregate span with summary statistics.

How it works: Spans are grouped by ${parentSpanId}:${spanName}. By default (emit: 'onInflightZero'), the group tracks in-flight count; when it drops to zero, the batch is complete and an aggregate span is emitted. If the same parent later starts another batch with the same name, it's a new group.

Error handling: By default, error spans are exported individually (full attributes, events, stack trace preserved) and counted in opin_tel.agg.error_count. Set keepErrors: false to consume error spans into the aggregate instead.

Single-span optimization: If only one non-error span arrives in a group (and no errors), it's exported as-is — no aggregate wrapper.

Emission modes

| Mode | Behavior | Best for | | ---------------------------- | ---------------------------------------------------- | --------------------------------------------- | | 'onInflightZero' (default) | Emits when all started spans in the group have ended | Parallel patterns (Promise.all) | | 'onParentEnd' | Defers emission until the parent span ends | Sequential loops (for/while with await) |

With the default onInflightZero, sequential spans each start and end before the next — inflight goes 1→0 every iteration, producing N separate aggregates of count=1. Use emit: 'onParentEnd' to keep the group open and aggregate all sequential children into one span.

Chunking

The chunk option emits intermediate aggregate spans at regular intervals, useful for long-running loops where you want periodic visibility without waiting for the parent to end.

• Number — emit every N spans: chunk: 100
• Predicate — emit when the function returns true: chunk: (span, stats) => stats.totalDurationMs > 5000

The predicate receives the current span and an AggregateGroupStats object (count, errorCount, nonErrorCount, totalDurationMs, minDurationMs, maxDurationMs).

Each chunk gets an opin_tel.agg.chunk_index attribute (0-based). After a chunk emits, the group stats reset for the next chunk. Any remaining spans are emitted when the group closes (parent end or inflight zero).

Chunking works with both emission modes.

Root-level predicate

opinionatedTelemetryInit({
  // Return true for default aggregation, or an AggregateConfig for custom stats
  aggregateSpan: (span) => {
    if (span.name.startsWith('S3.')) return true
    if (span.name === 'redis.cmd')
      return {
        attributes: {
          response_bytes: {
            attribute: 'redis.response_size_bytes',
            options: ['min', 'max', 'avg'],
          },
          all_statements: {
            attribute: 'db.statement',
            options: 'uniq',
          },
        },
      }
    // Sequential loop — aggregate all iterations under the parent
    if (span.name === 'process.record')
      return { emit: 'onParentEnd', chunk: 100 }
    return false
  },
})

Per-instrumentation

instrumentationHooks: {
  '@opentelemetry/instrumentation-dataloader': {
    aggregate: true,
  },
  // Or with custom attribute stats:
  '@opentelemetry/instrumentation-redis': {
    aggregate: {
      keepErrors: false,
      attributes: {
        sizes: {
          attribute: 'redis.response_size_bytes',
          options: ['min', 'max', 'range'],
        },
      },
    },
  },
}

Aggregate span attributes

Every aggregate span has opin_tel.meta.is_aggregate = true and the following built-in stats:

| Attribute | Description | | -------------------------------- | ------------------------------------------------------------- | | opin_tel.agg.count | Total spans in the group (including errors) | | opin_tel.agg.error_count | Number of spans with ERROR status | | opin_tel.agg.min_duration_ms | Shortest non-error span duration | | opin_tel.agg.max_duration_ms | Longest non-error span duration | | opin_tel.agg.avg_duration_ms | Mean non-error span duration | | opin_tel.agg.total_duration_ms | Sum of non-error span durations | | opin_tel.agg.chunk_index | 0-based chunk index (present only when chunk is configured) |

Custom attribute stat options

When you configure attributes, each entry maps an output key to a source attribute and one or more stat options. Stats are emitted as opin_tel.agg.{outputKey}.{stat}.

| Option | Input type | Description | | -------- | ---------- | ----------------------------------------------------- | | uniq | any | Array of unique values (converted to strings) | | count | any | Number of spans that had this attribute | | sum | numeric | Sum of values | | min | numeric | Minimum value | | max | numeric | Maximum value | | range | numeric | max - min | | avg | numeric | Mean value | | median | numeric | Median (average of two middle values for even counts) |

instrumentationHooks

Per-instrumentation hooks keyed by instrumentation scope name. Allows you to customize span behavior for specific instrumentations without wrapping them.

opinionatedTelemetryInit({
  instrumentations: [
    new HttpInstrumentation(),
    new KnexInstrumentation(),
    new DataloaderInstrumentation(),
  ],
  instrumentationHooks: {
    '@opentelemetry/instrumentation-knex': {
      collapse: true,
    },
    '@opentelemetry/instrumentation-dataloader': {
      aggregate: true,
    },
    '@opentelemetry/instrumentation-http': {
      onEnd: (span, durationMs) =>
        span.updateName(
          `${span.attributes['http.method']} ${span.attributes['http.route']} (${Math.round(durationMs)}ms)`,
        ),
    },
  },
})

Options per hook:

• collapse — drop this span, merge attrs into children, reparent children to grandparent
• aggregate — true or an AggregateConfig to collapse parallel sibling spans into a single aggregate
• onStart(span) — called during span start; use span.updateName() to rename, span.setAttribute() to enrich. Can return { collapse: true } to collapse this specific span, or { shouldDrop } to register conditional span dropping. If both are returned, collapse takes precedence.
• onEnd(span, durationMs) — called during span end (before export); durationMs is the span duration in milliseconds. Same span mutation APIs available

A warning is logged (via console.warn by default) if any hook key doesn't match a registered instrumentation name. Pass a custom logger to redirect or suppress these warnings.

globalHooks

Global hooks that fire for every span, regardless of instrumentation scope. Useful for cross-cutting concerns like conditional span dropping based on span attributes.

opinionatedTelemetryInit({
  // ...
  globalHooks: {
    onStart: (span) => {
      // Called on every span start
      // Can return { collapse: true } for per-span collapsing
      // Can return { shouldDrop } to register conditional dropping
    },
    onEnd: (span, durationMs) => {
      // Called on every span end, after enrichment
    },
  },
})

Both globalHooks.onStart and instrumentationHooks[scope].onStart can return { collapse: true } for per-span collapsing, or { shouldDrop } to register conditional span dropping — see below.

Conditional Span Dropping

Tail-based conditional span dropping allows you to register a shouldDrop callback at span start, then decide whether to drop the span when it ends — based on duration, error status, or any other span data.

Child spans are buffered while waiting for the parent's decision. When a span is dropped, its children are reparented to the grandparent. When kept, all buffered children are flushed normally.

Register via globalHooks.onStart or instrumentationHooks[scope].onStart:

opinionatedTelemetryInit({
  // ...
  globalHooks: {
    onStart: (span) => {
      // Drop pg-pool.connect spans unless they're slow or errored
      if (span.name === 'pg-pool.connect') {
        return {
          shouldDrop: (span, durationMs) => {
            if (span.status.code === SpanStatusCode.ERROR) return false // keep errors
            if (durationMs > 50) return false // keep slow connections
            return true // drop fast, successful connections
          },
        }
      }
    },
  },
})

shouldDrop return values

The shouldDrop callback returns a value controlling how the span is dropped:

| Return value | Behavior | | ------------ | -------------------------------------------------------------------------------------- | | false | Keep the span and all buffered children | | true | Drop the span, reparent children to grandparent (no attribute inheritance) | | 'collapse' | Drop the span like collapse: inherit attributes into children, reparent to grandparent |

true is the default drop mode — children are reparented but don't inherit the dropped span's attributes. Use 'collapse' when the dropped span has useful context that should flow down to children (similar to the collapse instrumentation hook option).

Nested conditional drops

When multiple ancestors have shouldDrop registered, decisions cascade: if a parent is dropped, its reparented children wait for the next ancestor's decision before being flushed. This works correctly with any combination of true and 'collapse' return values.

Interaction with collapse

If a span has both collapse and shouldDrop — whether from instrumentationHooks[scope].collapse: true, or from onStart returning both { collapse: true, shouldDrop } — collapse takes priority and shouldDrop is ignored. The span is dropped immediately with attribute inheritance, and any conditional buffer is flushed with reparenting to the collapse target.

Trace Counters

Root spans automatically receive counter attributes tracking drops and sampling decisions within their trace:

| Attribute | Description | | ------------------------------------ | --------------------------------------- | | opin_tel.trace.started_span_count | Total child spans started in this trace | | opin_tel.trace.captured_span_count | Child spans exported in this trace | | opin_tel.dropped.sync_count | Spans dropped by sync span detection | | opin_tel.dropped.conditional_count | Spans dropped by conditional dropping | | opin_tel.dropped.aggregated_count | Spans consumed by aggregation | | opin_tel.sampled.head_count | Spans dropped by head sampling | | opin_tel.sampled.tail_count | Spans dropped by tail sampling | | opin_tel.sampled.burst_count | Spans dropped by burst protection |

Counters are best-effort — they reflect drops that occurred before the root span ended. Only non-zero counters are written.

FilteringSpanProcessor

Span processor that handles sync span dropping, baggage propagation, span collapsing, conditional dropping, instrumentation hooks, and custom lifecycle hooks. Used internally by opinionatedTelemetryInit but can be used standalone. Accepts instrumentationHooks and globalHooks in its config.

Baggage utilities

import { withBaggage, getBaggageValue } from 'opinionated-telemetry'

// Set baggage and run in that context
withBaggage({ 'app.account_id': '123' }, () => {
  // Read baggage
  const accountId = getBaggageValue('app.account_id')
})

Trace-level context

Set attributes that apply to all spans in a trace. Useful for enriching spans with information discovered mid-trace (e.g. after user authentication), or when wrapping with baggage isn't feasible. Trace context attributes never overwrite existing span attributes — span-level values always take precedence.

When using tail-based sampling, trace context is applied retroactively to buffered spans before they are exported.

import { setTraceContext } from 'opinionated-telemetry'

// Inside any active span — attributes will appear on every span in this trace
setTraceContext({ 'user.id': userId, 'user.role': 'admin' })

getRootSpan()

Returns the root span of the active trace from anywhere in the call stack. The OTel API only provides trace.getActiveSpan() which returns the current span — there's no built-in way to reach the root from a child context.

Use this when you want to set attributes on the root span specifically, rather than on every span in the trace. Common use cases:

• Post-auth enrichment: after identifying a user in auth middleware, tag the root request span with user info so it shows up in the top-level trace view
• Request-level metadata: set final response status, resolved route, or feature flags on the root span from deeper in the call stack
• Computed summaries: add a summary attribute to the root after the work is done (e.g. total items processed)

import { getRootSpan } from 'opinionated-telemetry'

// In auth middleware, after identifying the user:
const root = getRootSpan()
if (root) {
  root.setAttribute('user.id', userId)
  root.setAttribute('app.plan', plan)
}

Returns undefined if there is no active span or the root span has already ended.

Auto-instrumentation

Auto-instrumentation hooks are opt-in imports, separate from the main entry point:

CJS (Module._load patching):

import { createAutoInstrumentHookCJS } from 'opinionated-telemetry/auto-instrument'

createAutoInstrumentHookCJS({
  // tracer is optional — defaults to trace.getTracer('opin_tel.auto')
  instrumentPaths: [
    { base: '/app/src', dirs: ['controllers', 'helpers', 'lib'] },
  ],
  ignoreRules: [
    'helpers/health-check',
    { file: 'helpers/utils', exports: ['internalFn'] },
  ],
})

ESM (requires --import @opentelemetry/instrumentation/hook.mjs):

import { createAutoInstrumentHookESM } from 'opinionated-telemetry/auto-instrument-esm'

const unhook = createAutoInstrumentHookESM({
  instrumentPaths: [
    { base: '/app/src', dirs: ['controllers', 'helpers', 'lib'] },
  ],
})

Filtering function wrapping

By default, all async function exports are wrapped. Use functionInstrumentation to customize:

createAutoInstrumentHookCJS({
  instrumentPaths: [{ base: '/app/src', dirs: ['controllers'] }],
  functionInstrumentation: {
    // Override the default AsyncFunction check (e.g. wrap promise-returning non-async fns)
    shouldWrap: (fn, name, filename) => fn.constructor.name === 'AsyncFunction',
    // Filter which exports to instrument: string[], RegExp, or function
    include: ['getUser', 'createOrder'],
  },
})

Class method instrumentation

Class method wrapping is opt-in via classInstrumentation. Spans are named filename/ClassName.methodName.

createAutoInstrumentHookCJS({
  instrumentPaths: [{ base: '/app/src', dirs: ['services'] }],
  classInstrumentation: {
    // Which classes to instrument (string[], RegExp, or function)
    includeClass: /Service$/,
    // Which methods to instrument (string[], RegExp, or function). Default: all async methods.
    includeMethod: (methodName) => !methodName.startsWith('_'),
    // Override the default AsyncFunction check
    shouldWrap: (fn, name, filename) => fn.constructor.name === 'AsyncFunction',
  },
})

Auto-instrument hooks

Both CJS and ESM hooks accept an optional hooks object with onStart and onEnd callbacks. These are called on every auto-instrumented function invocation with access to the function's arguments and return value, allowing you to enrich spans with call-specific context.

The context object is a discriminated union — check context.type to determine whether it's a function or method call:

createAutoInstrumentHookCJS({
  instrumentPaths: [{ base: '/app/src', dirs: ['controllers', 'services'] }],
  hooks: {
    onStart: (span, context) => {
      if (context.type === 'function') {
        // context.fnName, context.filename, context.args
        if (context.fnName === 'getUser') {
          span.setAttribute('app.user_id', context.args[0])
        }
      } else {
        // context.type === 'method'
        // context.className, context.methodName, context.filename, context.args
        span.setAttribute('app.class', context.className)
      }
    },
    onEnd: (span, context) => {
      // context also has: returnValue?, error?
      if (context.returnValue?.rows) {
        span.setAttribute('app.row_count', context.returnValue.rows.length)
      }
    },
  },
})

| Callback | Context fields (function) | Context fields (method) | | --------- | ------------------------------------------------ | --------------------------------------------------------------- | | onStart | type: 'function', args, fnName, filename | type: 'method', args, className, methodName, filename | | onEnd | Same as onStart + returnValue?, error? | Same as onStart + returnValue?, error? |

These hooks are for span enrichment only — use globalHooks or instrumentationHooks on the FilteringSpanProcessor for span lifecycle control (collapse, conditional dropping, etc.).

Honeycomb Quick Start

The opinionated-telemetry/honeycomb entrypoint wires up OTLP trace and metric exporters pointed at Honeycomb with sensible defaults, so you don't need to configure exporters manually.

import { honeycombInit } from 'opinionated-telemetry/honeycomb'
import { HttpInstrumentation } from '@opentelemetry/instrumentation-http'

const { sdk, getTracer, shutdown, runtimeMetrics } = honeycombInit({
  serviceName: 'my-service',
  apiKey: process.env.HONEYCOMB_API_KEY!,
  instrumentations: [new HttpInstrumentation()],
  // ... other options
})

This sets up:

• Trace export to https://api.honeycomb.io/v1/traces with dataset = serviceName
• Metric export via FlatMetricExporter to https://api.honeycomb.io/v1/metrics with dataset = ${serviceName}_metrics, collected every 60s
• Runtime metrics — 18 focused Node.js health gauges (event loop delay, heap, GC, CPU, handles, memory) auto-started unless runtimeMetrics: false

All other opinionatedTelemetryInit options are supported. traceExporter and metricExporter can be overridden if you need custom exporter configuration.

| Option | Type | Default | Description | | ------------------------ | ----------------------------------- | -------- | -------------------------------------------------------- | | apiKey | string | required | Honeycomb API key | | enableMetricCollection | boolean | true | Set to false to disable metric collection | | metricExportInterval | number | 60_000 | Metric export interval in milliseconds | | traceExporter | SpanExporter | — | Override the default OTLP trace exporter | | metricExporter | PushMetricExporter | — | Override the default OTLP metric exporter | | runtimeMetrics | NodeRuntimeMetricsConfig \| false | {} | Configure or disable runtime metrics (see section below) |

The entrypoint also re-exports everything from the main opinionated-telemetry package, so you can use it as your sole import.

Flat Metric Exporter

Honeycomb merges metric data points into a single event when they share the same timestamp, resource, and data point attributes. But metrics with different dimensional attributes (like v8js.heap.space.name=new_space vs v8js.gc.type=major) end up as separate events.

The FlatMetricExporter wraps your OTLPMetricExporter (or any PushMetricExporter) and transforms metrics before export:

1. Folds dimensional attributes into metric names — so all data points have the same (empty) attribute set
2. Expands histograms into individual gauge metrics with summary stats and percentiles

This ensures Honeycomb merges everything into one wide event per collection cycle.

import { FlatMetricExporter } from 'opinionated-telemetry/metrics'
import { PeriodicExportingMetricReader } from '@opentelemetry/sdk-metrics'
import { OTLPMetricExporter } from '@opentelemetry/exporter-metrics-otlp-proto'

const metricReader = new PeriodicExportingMetricReader({
  exporter: new FlatMetricExporter({
    exporter: new OTLPMetricExporter({
      url: 'https://api.honeycomb.io:443/v1/metrics',
      headers: { 'x-honeycomb-team': process.env.HONEYCOMB_API_KEY },
    }),
  }),
  exportIntervalMillis: 15_000,
})

Dimensional flattening

Metrics with dimensional attributes (like v8js.heap.space.name) are flattened by appending the dimension value to the metric name by default. Use renameDimension for custom naming:

new FlatMetricExporter({
  exporter: metricExporter,
  renameDimension: (metricName, dimKey, dimValue) => {
    if (dimKey === 'v8js.heap.space.name') {
      const short = dimValue.replace('_space', '')
      return metricName.replace('.heap.', `.heap_${short}.`)
    }
    if (dimKey === 'v8js.gc.type') {
      return metricName.replace('v8js.gc.', `v8js.gc_${dimValue}.`)
    }
    // Return undefined to use default (append _value)
  },
})

Histogram expansion

Histogram metrics are automatically expanded into summary stats and percentiles:

| Suffix | Description | | ----------------------------------------------- | ---------------------------- | | .count | Total number of observations | | .sum | Sum of all values | | .min | Minimum value | | .max | Maximum value | | .avg | Mean value (sum/count) | | .p50, .p75, .p90, .p95, .p99, .p999 | Percentiles (configurable) |

Customize percentiles via histogramPercentiles:

new FlatMetricExporter({
  exporter: metricExporter,
  histogramPercentiles: [0.5, 0.9, 0.95, 0.99],
})

Result

Instead of N separate metric events, you get a single wide event per collection cycle:

timestamp: 2026-03-06T19:31:01Z
socket.io.open_connections: 1
v8js.memory.heap_new.used: 220136
v8js.memory.heap_new.limit: 1048576
v8js.memory.heap_large_object.used: 23513056
v8js.gc_major.duration.count: 3
v8js.gc_major.duration.avg: 0.0105
v8js.gc_major.duration.p99: 0.015
...

Node Runtime Metrics

OTel's default runtime metrics packages (@opentelemetry/host-metrics + @opentelemetry/instrumentation-runtime-node) emit 24+ metrics with per-heap-space breakdowns, per-core CPU, per-NIC network stats, and all GC types. Most of this is noise.

NodeRuntimeMetrics replaces them with 18 focused, actionable gauges using built-in Node.js APIs, exposed through the OTel Meter API so they flow through the existing FlatMetricExporter pipeline.

When using the honeycombInit entrypoint, runtime metrics are auto-started by default. For standalone use:

import { NodeRuntimeMetrics } from 'opinionated-telemetry/metrics'

const rtm = new NodeRuntimeMetrics({
  // All options are optional
  prefix: 'node', // metric name prefix (default: 'node')
  eventLoopDelayResolution: 20, // histogram resolution in ms (default: 20)
  enable: {
    // selectively disable groups (all default true)
    eventLoopDelay: true,
    heap: true,
    gc: true,
    handlesRequests: true,
    cpu: true,
    memory: true,
  },
})

rtm.start() // idempotent
// ... later
rtm.stop() // idempotent — disconnects observers, disables histogram

Metrics

| Group | Metric | Source | | ---------- | ------------------------------ | ------------------------------------------------ | | Event Loop | node.eventloop.delay.p50 | monitorEventLoopDelay().percentile(50) (ms) | | | node.eventloop.delay.p99 | .percentile(99) (ms) | | | node.eventloop.delay.max | .max (ms) | | Heap | node.heap.used_mb | process.memoryUsage().heapUsed | | | node.heap.total_mb | .heapTotal | | | node.heap.used_pct | heapUsed / heapTotal * 100 | | GC | node.gc.major.count | PerformanceObserver('gc'), kind=2 (major) only | | | node.gc.major.avg_ms | average duration per interval | | | node.gc.major.max_ms | max duration per interval | | | node.gc.major.p99_ms | p99 duration per interval | | Handles | node.handles | process._getActiveHandles().length | | | node.requests | process._getActiveRequests().length | | CPU | node.cpu.user_pct | process.cpuUsage() delta | | | node.cpu.system_pct | delta | | | node.cpu.total_pct | user + system | | Memory | node.memory.rss_mb | process.memoryUsage().rss | | | node.memory.external_mb | .external | | | node.memory.array_buffers_mb | .arrayBuffers |

All metrics are observable gauges with zero attributes, so they merge cleanly into a single wide event when using FlatMetricExporter with Honeycomb.

Event loop and GC stats are reset after each observation, giving you per-interval measurements. CPU percentages are computed as deltas between observations.

Processor Diagnostic Metrics

The FilteringSpanProcessor exposes its internal state as OTel metrics — active spans, active traces, tail buffer depth, throughput counters, and drop breakdowns. These help detect span leaks, understand throughput, and monitor pipeline health.

Enabled by default. Set processorMetrics: false to disable.

opinionatedTelemetryInit({
  processorMetrics: false, // disable if not needed
})

Metrics include interval watermarks (current + max + min since last observation) for active spans and traces, snapshot gauges for stuck spans and aggregate groups, and per-interval throughput counters that reset on each collection.

See docs/PROCESSOR_METRICS.md for the full metric reference.

Metric Filtering

OTel's View API is the standard way to drop metrics, but it's verbose and limited to glob wildcards. opinionated-telemetry provides two simpler approaches that can be used independently or together.

Quick: metricFilter config

The simplest path — provide metricExporter instead of metricReaders and add a metricFilter:

import { OTLPMetricExporter } from '@opentelemetry/exporter-metrics-otlp-proto'

opinionatedTelemetryInit({
  serviceName: 'my-service',
  traceExporter: new OTLPTraceExporter(),
  instrumentations: [new HttpInstrumentation()],
  metricExporter: new OTLPMetricExporter({
    url: 'https://api.honeycomb.io:443/v1/metrics',
    headers: { 'x-honeycomb-team': process.env.HONEYCOMB_API_KEY },
  }),
  metricFilter: {
    drop: [
      'http.server.*', // glob pattern
      /^node\.gc/, // regex
      (name) => name.endsWith('.p99'), // predicate
    ],
    // OR allowlist — only matching metrics are kept:
    allow: ['opin_tel.*', 'node.heap.*', 'node.cpu.*'],
  },
})

metricExporter is a shorthand that creates the PeriodicExportingMetricReader for you. Use metricExportInterval to override the default 60s interval. Mutually exclusive with metricReaders.

Pattern types (MetricPattern = string | RegExp | ((name: string) => boolean)):

| Type | Example | Behavior | | ------------- | --------------------------------- | --------------------------------------- | | String (glob) | 'http.server.*' | * matches any sequence of characters | | RegExp | /^node\.gc/ | Standard regex test against metric name | | Predicate | (name) => name.endsWith('.p99') | Return true to match |

drop vs allow:

• drop — metrics matching any pattern are excluded
• allow — only metrics matching at least one pattern are kept
• Both can be combined: allow filters first, then drop removes from the allowed set

How it works: String glob patterns in drop generate efficient DROP Views (metrics are never collected — zero overhead). Regex, predicates, and allow patterns are applied at the exporter level via FilteringMetricExporter, which requires metricExporter for automatic wiring.

Standalone: dropMetrics() helper

If you use metricReaders directly and just need to drop a few metrics, dropMetrics() generates ViewOptions[] with DROP aggregation:

import { dropMetrics } from 'opinionated-telemetry/metrics'

opinionatedTelemetryInit({
  metricReaders: [myReader],
  views: [
    ...dropMetrics('http.server.*', 'http.client.*', 'node.gc.*'),
    ...flatMetricExporterViews,
  ],
})

This is the most efficient approach (zero collection overhead) but only supports string glob patterns.

Standalone: FilteringMetricExporter

For full control, wrap any PushMetricExporter with FilteringMetricExporter. Supports all pattern types and both drop/allow:

import {
  FilteringMetricExporter,
  FlatMetricExporter,
} from 'opinionated-telemetry/metrics'
import { PeriodicExportingMetricReader } from '@opentelemetry/sdk-metrics'

const reader = new PeriodicExportingMetricReader({
  exporter: new FilteringMetricExporter({
    exporter: new FlatMetricExporter({ exporter: otlpExporter }),
    drop: [/^node\.gc/],
    allow: ['opin_tel.*', 'node.heap.*', 'node.cpu.*'],
  }),
})

Sampling

opinionated-telemetry includes built-in sampling with three composable modes: head-based, tail-based, and EMA burst protection. See SAMPLING.md for detailed documentation on the philosophy, algorithms, composition, and design decisions.

opinionatedTelemetryInit({
  serviceName: 'my-service',
  traceExporter: new OTLPTraceExporter(),
  instrumentations: [new HttpInstrumentation()],
  sampling: {
    // Head-based: lightweight, immediate drop/keep at trace start
    head: {
      sample: (attrs, spanName) => {
        if (spanName.startsWith('health-check')) return 100 // keep 1-in-100
        return 1 // keep all
      },
      mustKeepSpan: (span, durationMs) =>
        span.status.code === SpanStatusCode.ERROR,
    },

    // Tail-based: buffer all spans, decide with full trace context
    tail: {
      sample: (rootAttrs, trace) => {
        if (trace.hasError) return 1 // keep all errors
        if (trace.durationMs > 5000) return 1 // keep slow traces
        return 10 // sample 1-in-10 otherwise
      },
      mustKeepSpan: (span, durationMs) =>
        span.status.code === SpanStatusCode.ERROR,
      maxTraces: 1000, // max buffered traces (default: 1000)
      maxAgeMs: 120_000, // max buffer age (default: 120s)
      maxSpansPerTrace: 500, // flush large traces early (default: 500)
    },

    // Burst protection: EMA-based per-key throttling
    burstProtection: {
      keyFn: (span) => span.name, // grouping key (default: span.name)
      halfLifeMs: 10_000, // EMA responsiveness (default: 10s)
      rateThreshold: 100, // spans/sec before throttling (default: 100)
      maxSampleRate: 100, // max sample rate cap (default: 100)
    },
  },
})

Head-based sampling calls sample once per root span and returns a 1-in-N rate. Spans are dropped immediately if sampled out. mustKeepSpan(span, durationMs) can rescue individual important spans (e.g. errors, slow spans) by reparenting them to the root with SampleRate=1.

Tail-based sampling buffers all spans until the root ends, then calls sample with a TraceSummary containing error counts, duration, and span count. mustKeepSpan(span, durationMs) flags a trace for guaranteed keeping without short-circuiting the buffer. Safety valves (maxTraces, maxAgeMs, maxSpansPerTrace) prevent unbounded memory growth.

Burst protection uses an exponential moving average to detect per-key span rate spikes and automatically applies a sample rate when throughput exceeds the threshold. No manual rate configuration needed.

When combined, rates compose multiplicatively. Tail overrides head for the base decision. mustKeepSpan always clamps the rate to 1. Kept spans receive a SampleRate=N attribute following the Honeycomb convention.

onDroppedSpan

Called whenever a span is dropped due to sync span dropping, conditional dropping, sampling, burst protection, or stuck span eviction via 'drop'. Useful for writing sampled-out spans to a compressed ndjson file or other secondary storage for later retrieval.

opinionatedTelemetryInit({
  // ...
  onDroppedSpan: (span, reason, durationMs) => {
    // reason: 'head' | 'tail' | 'burst' | 'sync' | 'conditional' | 'stuck'
    // durationMs: provided for 'tail', 'burst', 'conditional', and 'stuck' drops
    droppedSpanLog.write(
      JSON.stringify({
        name: span.name,
        traceId: span.spanContext().traceId,
        reason,
        attributes: span.attributes,
        durationMs,
      }) + '\n',
    )
  },
})

onCapturedSpan

Called whenever a span is accepted and forwarded to the underlying exporter. The mirror of onDroppedSpan — useful for logging, metrics, or debugging which spans make it through filtering and sampling.

opinionatedTelemetryInit({
  // ...
  onCapturedSpan: (span, durationMs) => {
    capturedSpanLog.write(
      JSON.stringify({
        name: span.name,
        traceId: span.spanContext().traceId,
        durationMs,
        attributes: span.attributes,
      }) + '\n',
    )
  },
})

SQL Utilities

Reusable helpers for normalizing SQL queries and generating CRC32 etags for caching/dedup. Handles multiple binding styles (?, $1, ?::type, $1::type, DEFAULT).

import {
  stabilizeQuery,
  queryRequestTag,
  stableQueryTag,
  queryResponseTag,
  stableQueryHash,
} from 'opinionated-telemetry'

stabilizeQuery(sql): StableQueryResult

Regex-normalizes SQL by collapsing variadic binding groups into stable placeholders. Single groups like (?, ?, ?) become (_), multiple consecutive groups like (_), (_), (_) become (_+).

const result = stabilizeQuery(
  'INSERT INTO t (a, b) VALUES (?, ?), (?, ?), (?, ?)',
)
// result.stableQuery === 'INSERT INTO t (a, b) VALUES (_+)'
// result.groupCount === 3
// result.groupedBindingCount === 6

Returns { stableQuery: string, groupCount: number, groupedBindingCount: number }.

queryRequestTag(sql, bindings?): string

CRC32 hash of the raw SQL + actual bindings — exact cache key for dedup of identical invocations.

stableQueryTag(sql, bindings?): string

CRC32 of the stabilized SQL + sanitized binding types — groups queries by shape. Same structure with same binding types produces the same tag, regardless of actual values.

queryResponseTag(result, maxBytes?): string

CRC32 hash of JSON.stringify(result). Optional maxBytes truncates the serialized result before hashing.

stableQueryHash(sql): string

CRC32 of just the stabilized query text — for grouping queries by shape regardless of binding count or values.

Integration Helpers

Each integration is a separate entry point to avoid pulling unnecessary dependencies.

Express

Middleware that enriches the active OTel span with request metadata (method, path, query string, headers) and optionally propagates select values as baggage so they appear on all downstream child spans.

import { otelCreateExpressMiddleware } from 'opinionated-telemetry/integrations/express'

app.use(
  otelCreateExpressMiddleware({
    captureHeaders: ['user-agent', 'x-request-id'],
    baggageHeaders: ['x-request-id'],
    captureQueryParams: ['page', 'search'],
    baggageQueryParams: ['page'],
    requestHook: (req, { setAttribute, setAsBaggage }) => {
      if (req.user?.id) setAsBaggage('app.user.id', req.user.id)
    },
  }),
)

| Option | Description | | -------------------- | ----------------------------------------------------------------------------------------------------------------------------- | | captureHeaders | Request headers to capture as req.header.<name> span attributes | | baggageHeaders | Subset of captureHeaders to also propagate as baggage | | captureQueryParams | Query params to capture as req.query.<name> span attributes | | baggageQueryParams | Subset of captureQueryParams to also propagate as baggage | | requestHook | Custom hook with setAttribute and setAsBaggage helpers for extracting additional request context (e.g. user ID from auth) | | enabled | Enable/disable the middleware. Default: true |

Security: baggageHeaders and baggageQueryParams values are propagated as OTel baggage. With the default baggagePropagation config, outbound baggage is suppressed. If you configure allowedHosts, be careful not to include sensitive headers (e.g. authorization, cookie) in baggageHeaders — they would be sent to those hosts in the baggage HTTP header.

Knex

Listens to knex query events and enriches the active span with connection ID, transaction ID, pool stats, and sanitized query bindings. Bindings are sanitized by replacing strings with string<length> and class instances with <<Object#ClassName>> to avoid leaking sensitive data.

Returns a cleanup function to remove the listener.

import { otelInitKnex } from 'opinionated-telemetry/integrations/knex'
import { queryRequestTag } from 'opinionated-telemetry'

const cleanup = otelInitKnex(knexInstance, {
  captureBindings: true,
  capturePoolStats: true,
  queryHook: ({ sql, bindings, stable, setAttribute }) => {
    setAttribute('db.query.request_tag', queryRequestTag(sql, bindings))
    setAttribute('db.query.method', sql.split(' ')[0].toUpperCase())
  },
})

// Later: cleanup() to remove the listener

| Option | Description | | ------------------ | -------------------------------------------------------------------------------------------------------------------------------- | | captureBindings | Capture sanitized bindings as db.query.sanitized_bindings and a CRC32 hash as db.query.hash. Default: true | | capturePoolStats | Capture connection pool stats (db.pool.used_count, db.pool.free_count, etc.). Default: true | | hashFn | Custom hash function for query+bindings. Default: CRC32 via node:zlib | | queryHook | Custom hook called per query with { sql, bindings, stable, setAttribute }. Use to set additional attributes like request tags. |

Span attributes set: db.connection.id, db.tx.id, db.timeout, db.query.stable (stabilized SQL shape), db.query.stable_hash (CRC32 of stable shape), db.query.group_count, db.query.grouped_binding_count, db.query.sanitized_bindings, db.query.hash, db.pool.*.

GraphQL

Wraps custom resolve functions in a GraphQL schema with OTel context propagation. For each resolver call, extracts graphql.* attributes from the active span and propagates them as baggage, so downstream spans (e.g. database queries triggered by a resolver) inherit the GraphQL operation context.

Skips fields using the default field resolver (i.e. simple property access).

import { defaultFieldResolver } from 'graphql'
import { otelInitGraphql } from 'opinionated-telemetry/integrations/graphql'

otelInitGraphql(schema, {
  fieldResolver: defaultFieldResolver,
  shouldWrapResolver: ({ typeName, fieldName }) => {
    return typeName !== 'InternalType'
  },
})

| Option | Description | | -------------------- | ---------------------------------------------------------------------------------------------------------------------- | | fieldResolver | Required. Pass defaultFieldResolver from graphql — used to identify which fields have custom resolvers | | shouldWrapResolver | Optional filter. Return false to skip wrapping a resolver. Receives { field, fieldName, type, typeName, resolver } |

Bull

Patches Bull.prototype to trace job processing with span links connecting producers to consumers across separate traces. This avoids creating artificially long parent-child traces for async job queues.

• .add() captures the current span context and stores it in the job data
• .process() creates a new root span with a span link back to the enqueuing span
• .on() wraps async event handlers with spans for lifecycle events

Call before any queues are created. Pass the Bull constructor (not an instance).

import Bull from 'bull'
import { otelInitBull } from 'opinionated-telemetry/integrations/bull'

otelInitBull(Bull, {
  tracerName: 'my-bull-tracer',
  tracedEvents: ['completed', 'failed'],
})

| Option | Description | | -------------- | ---------------------------------------------------------------------------------------------- | | tracerName | Tracer name for bull spans. Default: 'bull-otel' | | tracedEvents | Events to wrap with spans on .on(). Default: ['completed', 'stalled', 'failed', 'waiting'] |

Socket.IO

Two functions for Socket.IO observability:

• otelInitSocketIo(io) sets up an observable gauge tracking open connection count (socket.io.open_connections)
• otelPatchSocketIo(socket, config) patches a socket's .on() to inject baggage context into all event handlers, so spans created during socket events inherit user/session context

import {
  otelInitSocketIo,
  otelPatchSocketIo,
} from 'opinionated-telemetry/integrations/socket-io'

// Set up connection count gauge
otelInitSocketIo(io)

// Patch each socket for baggage propagation
io.on('connection', (socket) => {
  otelPatchSocketIo(socket, {
    getBaggage: (s) => ({ 'app.user.id': s.data?.userId }),
  })
})

| Option | Description | | ------------ | -------------------------------------------------------------------------------------- | | meterName | Meter name for the connection gauge. Default: 'socket-io-otel' | | getBaggage | Required. Function returning baggage entries to inject into event handler contexts |

Testing Utilities

opinionated-telemetry/testing provides TestSpanExporter and TestMetricExporter — drop-in OTel exporter implementations with built-in assertion helpers, search utilities, and ASCII span tree rendering.

import {
  TestSpanExporter,
  TestMetricExporter,
} from 'opinionated-telemetry/testing'

const exporter = new TestSpanExporter()

// ... run your code ...

exporter.assertNoErrors()
exporter.assertNoOrphanSpans()
exporter.assertSpanExists('GET /api/users')
exporter.assertSpanCount('db.query', 3)
exporter.assertSpanAttributes('GET /api/users', { 'http.method': 'GET' })

console.log(exporter.toTree())
// GET /api/users
// ├── middleware - auth
// ├── db.query SELECT users
// └── serialize response

See docs/TESTING.md for the full API reference.

License

MIT