monguard

Runtime MongoDB query intelligence for Mongoose. Drop in one plugin and monguard analyzes every query your app runs — slow queries, missing indexes, N+1 hot-paths, duplicate fetches, aggregation pipelines that sort before they match, and more — with terminal warnings and a programmatic stats API.

Why

Most MERN apps ship without anyone ever looking at query plans. Existing tooling (Atlas Profiler, Datadog APM, Sentry Performance) is heavy, requires dashboards, and costs money. monguard is the smallest possible thing that runs in your dev (or prod) process, in-band, and tells you exactly what to fix.

Install

npm install @mr-aftab-ahmad-khan/monguard

(mongoose is a peer dependency — works with v7 and v8.)

Use globally on every model

import mongoose from "mongoose";
import { monguard } from "@mr-aftab-ahmad-khan/monguard";

const sense = monguard({
  slowQueryThreshold: 300,
  duplicateThreshold: 5,
  duplicateWindowMs: 1000,
});

mongoose.plugin(sense.plugin);

Or attach to one schema only:

import { Schema, model } from "mongoose";
import { monguard } from "@mr-aftab-ahmad-khan/monguard";

const userSchema = new Schema({ email: String, name: String });
userSchema.index({ email: 1 });

const sense = monguard();
userSchema.plugin(sense.plugin);

export const User = model("User", userSchema);

What it detects

| Warning | Triggered when | | --- | --- | | slow-query | a query exceeds slowQueryThreshold ms | | full-collection-scan | a read op runs with an empty filter | | missing-index | a filter targets fields not covered by any registered index | | duplicate-query | the same fingerprinted query fires >= duplicateThreshold times within duplicateWindowMs | | n-plus-one | duplicates exceed 2× duplicateThreshold (escalated severity) | | large-result | result set crosses largeResultThreshold | | aggregation-bottleneck | pipeline sorts/joins before $match, or sorts without $limit | | missing-projection | reads have no projection at all (opt-in) |

Example terminal warning:

[monguard WARN] Missing index on users for fields [tenantId, status].
  → Add an index: { status: 1, tenantId: 1 }
  op=find duration=412ms collection=users

Programmatic API

const sense = monguard({ slowQueryThreshold: 200 });

mongoose.plugin(sense.plugin);

sense.onWarning((w) => {
  alerting.send(w.kind, w.message, { collection: w.query.collection });
});

setInterval(() => {
  console.log(sense.stats());
  // { totalQueries, slowQueries, warnings: { 'slow-query': 12, ... }, topSlow, topDuplicate }
}, 60_000);

Reset between requests/tests:

sense.reset();

Options

monguard({
  slowQueryThreshold: 200,          // ms
  duplicateWindowMs: 1000,
  duplicateThreshold: 5,
  largeResultThreshold: 1000,
  warnOnFullScan: true,
  warnOnMissingIndex: true,
  warnOnMissingProjection: false,
  attachStackTrace: false,          // adds .stack to QueryEvent
  silent: false,                    // suppress logger
  logger: (line) => myLogger.warn(line),
  topSlowSize: 25,
  topDuplicateSize: 25,
});

Pure helpers (no mongoose required)

import {
  extractFilterFields,
  indexCoversFields,
  isFullScan,
  suggestCompoundIndex,
  fingerprintQuery,
  Analyzer,
} from "@mr-aftab-ahmad-khan/monguard";

Use the Analyzer directly to integrate with any DB layer.

Roadmap

• AI-powered fix suggestions
• Web dashboard
• Cloud-hosted aggregation
• Automated db.collection.createIndex runner

License

MIT