Local labs · 4 tools
See what
the code does.
Change the data, follow the states and take the result with you. No account is needed, and nothing leaves your browser.
Input → Code → Output
Run a function from a closed registry of curated utilities. Edit JSON, try edge cases and inspect actual output.
Recipe builder
Choose a supported task and environment. Get complete files, prerequisites, tests and a context package.
Delivery & retries
Step through API acceptance, an uncertain response, a retry and a duplicate avoided.
Webhook signatures
Sign a synthetic delivery event, then watch a re-serialized body, a tampered byte or a late replay fail verification.
Designed to be bounded
The code lab runs curated functions, not arbitrary JavaScript. The recipe builder generates files and never asks for a real API key. The delivery lab uses a virtual clock and clearly labeled synthetic events. The signature lab signs a published fixture with your browser’s Web Crypto; it never asks for a real secret.
Read the verification method