fast-json-rules-engineSame rules JSON, compiled once

A compiled, synchronous, zero-dependency engine for the json-rules-engine rule format — no promises, no clones.

⚡

Compiled, not interpreted

compile(rules) once into plain predicate functions; engine.run(facts) is synchronous — no Promise or clone overhead per evaluation.

🔁

Speaks json-rules-engine

Same rule JSON, same events output. Verified by differential fuzzing against json-rules-engine 6.6.0, whose rule-evaluation core is unchanged through current 7.x.

📦

Zero dependencies, Node 14+

CJS + ESM with bundled types in a ~18 kB unpacked dist. Runs on stacks that can't adopt json-rules-engine 7's Node 18 / ESM-only requirements.

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Honest benchmarks

~190× faster when you compile once and reuse; ~13× compiling fresh per call. Synthetic 30-rule set — the bench script ships in the repo, point it at your own rules.

Quick start

npm install fast-json-rules-engine

import { compile } from 'fast-json-rules-engine'

const rules = [
  {
    conditions: {
      all: [
        { fact: 'country', operator: 'in', value: ['US', 'GB', 'CA'] },
        { fact: 'spend', operator: 'greaterThanInclusive', value: 100 },
      ],
    },
    event: { type: 'whale', params: { tier: 'gold' } },
    priority: 10,
  },
]

// Compile once (e.g. when your config loads), reuse for every request.
const engine = compile(rules)

const { events } = engine.run({ country: 'US', spend: 250 })
// events -> [{ type: 'whale', params: { tier: 'gold' } }]

engine.run(facts) returns synchronously — no await, no .then(). Rules are near-static and facts change every call, so the pattern is always compile once, run many.

What it trades away

The speed comes from dropping json-rules-engine's runtime dynamism: async facts, event handlers, the evaluated conditions tree, and mutating rules on a live engine are deliberately not supported — recompile instead of patching a running engine. If your facts are plain values and you evaluate the same rules over and over, that trade is usually free. See the migration guide for the full compatibility matrix.