A deterministic feature-flag workbench for designing targeting rules, testing user contexts, and understanding percentage rollouts before configuration reaches production.
- ordered targeting rules with explicit precedence;
- stable percentage rollouts based on the flag key and subject key;
- a step-by-step evaluation trace for every decision;
- cohort exploration across representative users;
- independent production and staging configurations;
- versioned local persistence plus JSON copy and export;
- keyboard-accessible controls and reduced-motion support.
Everything runs locally in the browser. ToggleBench makes no API calls, loads no analytics, and sends no evaluation contexts to a server.
Each evaluation follows the same short pipeline:
- Return the control variation when the flag is disabled.
- Evaluate enabled targeting rules in order and return the first match.
- Hash
flag-key:subject-keyinto one of 10,000 stable buckets. - Return treatment when the bucket is inside the configured rollout; otherwise return control.
The FNV-1a hash is intentionally small and inspectable. It is appropriate for this deterministic simulator, but production flag platforms should use their documented bucketing algorithm to preserve SDK compatibility.
Requires Node.js 24+.
corepack enable
pnpm install
pnpm devRun the complete local gate:
pnpm lint
pnpm test
pnpm buildThe test suite covers operator normalization, rule precedence, disabled flags, stable hashing, rollout distribution, versioned persistence, environment switching, and interactive rule controls. GitHub Actions repeats lint, tests, and a production build for every pull request.
Evaluation and persistence live in pure TypeScript modules under src/lib. React owns configuration and context state, derives decisions during render, and persists only the versioned flag document. The interface uses no charting or state-management dependency, keeping the runtime bundle compact and the decision path easy to audit.
Tags matching v* run the full gate, build the static site, and publish a compressed release artifact. GitHub Pages deploys only from a successful build of main. To roll back the live site, revert the responsible commit on main; the Pages workflow will redeploy the previous configuration.
MIT © Hassan Ak