showwhat

An extensible schema and rule based evaluation engine for feature flags and configuration.

Define feature configs as variations with conditions in a YAML or JSON. At runtime, showwhat evaluates the conditions against a context object and resolves the first matching variation's value — booleans, strings, numbers, or full objects. No platform, no infrastructure, no vendor lock-in.

Documentation · Quick Start

Packages

Package	Description
showwhat	Resolution engine and main API
@showwhat/core	Rule engine, schemas, parsers, and in-memory data source
@showwhat/configurator	React UI library for visual rule editing
@showwhat/openfeature	OpenFeature provider integration
@showwhat/webapp	Web app for managing definitions
@showwhat/docs	Documentation site

Quick start

pnpm install showwhat
pnpm add showwhat
yarn add showwhat

# Other runtimes
bun add showwhat
deno install npm:showwhat

import { showwhat, MemoryData } from "showwhat";

const data = await MemoryData.fromYaml(`
definitions:
  checkout_v2:
    variations:
      - value: true
        conditions:
          - type: env
            value: prod
      - value: false
`);

const result = await showwhat({
  key: "checkout_v2",
  context: { env: "prod" },
  options: { data },
});

console.log(result.value); // true

Definition format

Definitions are YAML or JSON documents with a definitions root key. Each definition has one or more variations evaluated in order — the first matching variation wins. The format is portable: store it in a file, serve it from an API, or manage it in Git with PR reviews as your governance layer.

definitions:
  my_flag:
    variations:
      - value: "on"
        conditions:
          - type: env
            value: [prod, staging]
      - value: "off" # default (no conditions = always matches)

Built-in condition types

env · string · number · bool · datetime · startAt · endAt · and · or

See the Conditions guide for full details.

Security

showwhat assumes definition authors are trusted. See the Security guide for considerations when accepting definitions from untrusted sources.

AI Usage Disclosure

Parts of the codebase, tests, and documentation have been refined with AI assistance, with all outputs reviewed by humans. See CONTRIBUTING.md for guidelines.

License

MIT