Fastly Fiddle — Real-Edge VCL Testing

Trigger and scope

Trigger on: Fastly Fiddle, fiddle.fastly.dev URLs, the Fiddle HTTP API, CI testing of VCL services, real-edge VCL tests, shareable VCL reproductions, clientFetch.*/events.*/originFetches.* test expressions, .test.js / Mocha specs that target fiddles, SSE updateResult / waitingForSync events, remote VCL linting via Fiddle, or validating real Fastly behavior (geo, WAF, ESI, clustering, shielding) that local tools cannot simulate.

Do NOT use for: local VCL unit testing (use falco), fast TDD loops (Fiddle has a 10-20s edge-sync floor per publish), Fastly Compute/Wasm testing (use viceroy or fastlike), production service deployment (use fastly-cli), or anything requiring authenticated Fastly API access — Fiddle does not use your Fastly API key.

Fastly Fiddle is a web-based sandbox at https://fiddle.fastly.dev that compiles and runs VCL on real Fastly edge nodes. Because it uses the production VCL compiler and real POPs, it's the only way outside a real service to test VCL features that depend on edge infrastructure — geolocation data, WAF, ESI, clustering, shielding, rate limiting, real TLS, and real cache behavior.

Official UI: https://fiddle.fastly.dev Demo CI runner: https://github.com/fastly/demo-fiddle-ci API base: https://fiddle.fastly.dev (undocumented but stable; no auth required for public fiddles)

When Fiddle, when Falco