Umpire •

Get your app to play by the rules

Umpire is a declarative field-availability engine. Define fields, declare rules between them, and Umpire tells you which fields are in play — and which stale values just fell out. It answers a structural question, not a validation question: given the current values and conditions, what should be enabled right now?

Forms are the most common use case, but Umpire works anywhere state fits a plain object with interdependent options — game boards, config panels, pricing calculators, permission matrices. If it has fields and rules, Umpire can call the game.

Docs • GitHub

Quick Example

import { requires, umpire } from '@umpire/core'

const ump = umpire({
  fields: {
    password: {},
    confirmPassword: {},
  },
  rules: [requires('confirmPassword', 'password')],
})

ump.check({ password: '', confirmPassword: '' }).confirmPassword
// { enabled: false, satisfied: false, fair: true, required: false, reason: 'requires password', reasons: ['requires password'] }

ump.check({ password: 'hunter2', confirmPassword: '' }).confirmPassword
// { enabled: true, satisfied: false, fair: true, required: false, reason: null, reasons: [] }

For a larger example with conditions, plan-gated fields, and play() transitions, see the Signup example in the docs.

Packages

Package	Purpose
@umpire/core	Pure logic engine with zero runtime dependencies
@umpire/dsl	Pure expression DSL (expr.*, compileExpr, getExprFieldRefs)
@umpire/react	useUmpire() hook for React
@umpire/solid	useUmpire() hook for Solid
@umpire/signals	Signal adapter via SignalProtocol (Jotai, Preact, Alien Signals, TC39)
@umpire/store	Generic store adapter — bring your own getState() + subscribe(next, prev)
@umpire/zustand	Zustand adapter (satisfies the store contract natively)
@umpire/redux	Redux / Redux Toolkit adapter
@umpire/tanstack-store	TanStack Store adapter
@umpire/pinia	Pinia adapter
@umpire/vuex	Vuex 4 adapter
@umpire/zod	Availability-aware Zod schemas — disabled fields produce no errors
@umpire/reads	Derived read tables and read-backed rule bridges
@umpire/write	Create/patch write-policy checks against Umpire availability
@umpire/drizzle	Drizzle table hydration for Umpire fields plus write-policy re-exports
@umpire/testing	Invariant probes for rule configurations
@umpire/devtools	In-app inspector panel — scorecard, traces, foul log, graph view
@umpire/json-schema	JSON Schema composition profile — independent structural + availability

Why Umpire?

• Pure logic, zero dependencies.
• Declarative rules: requires, disables, enabledWhen, fairWhen, oneOf.
• Recommendations, not mutations: play() suggests resets, you decide when to apply them.
• Adapters for React, Solid, Zustand, Redux, TanStack Store, Pinia, Vuex, and signals.
• Debuggable: challenge() traces why any field was ruled out, @umpire/devtools surfaces it visually.

Install

npm install @umpire/core

Published packages do not require Bun to consume.

Contributing

Local repo work expects:

• Node 24+
• Yarn 4
• Bun 1.2+

yarn test and yarn test:coverage use Bun under the hood, so those commands will fail if Bun is not installed.

Docs

Full docs, concepts, and examples live at https://umpire.tools/

Droid-Friendly

Each published package ships a tight AGENTS.md file for cross-agent discoverability, with .claude/rules/* included as a Claude-specific compatibility surface. In this repo, AGENTS.md is canonical and CLAUDE.md plus .cursor/rules/ are compatibility symlinks.

Status

Stable — v1.0.0

License

MIT