prompt-lab

Same prompt, three Claude models, side by side. Sees latency and token usage so you can pick the right model for the job. Browser-only — your Anthropic API key lives in localStorage, never touches any server I run.

Anthropic API key

Prompt

Advanced

System prompt (optional) Max tokens Temperature

About the API key

The key stays in your browser's localStorage on this origin only. Clearing site data wipes it.
Each request goes directly from your browser to api.anthropic.com — no proxy. The Anthropic API allows browser-direct calls when the anthropic-dangerous-direct-browser-access: true header is set.
Open the source: api.js is ~150 lines, script.js is the UI. No telemetry, no third-party scripts.
Generate a key at console.anthropic.com/settings/keys.