@mikrojs/schema

The schema DSL behind Mikro.js: declare a shape once, infer its TypeScript type, validate values against it, and serialize it as plain JSON for something else to read. Zero dependencies, no Node APIs, so it runs on Node, Bun, Deno, Cloudflare Workers and in a browser.

Apps on a device import mikro/schema instead, which is this same DSL backed by a native module plus a Result-returning parse(). This package is the host half: the CLI evaluating mikro.config.ts, a registry validating what an operator saves, and anything else that needs to read a published schema.

import {number, object, string, validate} from '@mikrojs/schema'

const Config = object({
  mqttUrl: string({title: 'Broker URL', format: 'url'}),
  interval: number({title: 'Publish interval', unit: 's', default: 60, min: 1, max: 3600}),
})

validate(Config, {mqttUrl: 'mqtt://box.local', interval: 60}, '') // => null
validate(Config, {mqttUrl: 'mqtt://box.local', interval: 0}, '')
// => {ok: false, error: {name: 'ValidationFailed', message: 'below the minimum of 1', path: '.interval'}}

validate() returns null when the value is good, and covers shape plus every numeric and length bound. format is not checked here; see @mikrojs/schema/config.

Annotations

Nodes carry annotations, and they divide in two. Display annotations (title, description, mask) describe how a value should be presented and never change what validates, so a consumer may ignore any it does not recognise. Constraints (min, max, integer, minLength, maxLength, minItems, maxItems, format, unit) do change what validates, and a consumer must not ignore one it does not recognise: ignoring a constraint means accepting a value the author ruled out.

unit is a closed enum following SenML with ASCII keys. It is a display hint and constrains nothing. Never convert a stored value through a unit's scale — see the note beside UNITS.

@mikrojs/schema/config

The host-side machinery for Mikro.js OTA config, which is what a registry needs:

• validateConfig(schema, value) — validate() plus format, returning {ok, value} or {ok: false, error}
• parseConfigSchema(value) — validate a schema that arrived as JSON, rejecting malformed annotations and unknown format or unit values
• deriveOverlay / parseEffective / materializeDefaults — the sparse-overlay model, where a registry stores only deviations from the author's defaults and serves the complete document
• diffConfigSchemas(previous, next) — what changed between two releases, and whether it needs an operator's attention
• UNITS, FORMATS — the unit table and the format names

format lives here rather than in the main entry for two reasons: the expressions are a denial-of-service surface a device should not carry, and a device has no regular-expression engine to carry them with.

The wire format is the contract. It is specified in the OTA Registry Spec under "The config schema", and that document, not this package's version number, is what a third-party registry should build against.

Documentation

mikrojs.dev/api/schema