Skill

viceroy

Runs Fastly Compute WASM apps locally with Viceroy for Rust and Component Model projects. Use for dev servers, fastly.toml backend/store config, cargo-nextest tests, local debugging, module adaptation, and testing issues.

Rust

testing

devops

npx claudepluginhub fastly/fastly-agent-toolkit --plugin fastly-agent-toolkit

Tool Access

This skill uses the workspace's default tool permissions.

Preview

Viceroy is Fastly's official local testing environment for Compute applications. It emulates the Fastly Compute platform, allowing you to develop and test WASM services locally.

Supporting Assets

references/fastly-compute-adapt.mdreferences/fastly-compute-config.mdreferences/fastly-compute-serve.mdreferences/fastly-compute-test.md

SKILL.md

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Viceroy — Local Fastly Compute Runtime

Viceroy is Fastly's official local testing environment for Compute applications. It emulates the Fastly Compute platform, allowing you to develop and test WASM services locally.

Common Gotchas

Dictionaries and ConfigStores are both supported but configured differently in fastly.toml. Dictionaries go under [local_server.dictionaries] as inline key-value maps or JSON files. ConfigStores go under [local_server.config_stores].

fastly.toml must have a [local_server] section. Without it, Viceroy won't know about your backends, stores, or other local overrides. Every backend your app calls must be listed under [local_server.backends].

Default port is 7676, not 5000 (which is Fastlike's default). Access your app at http://127.0.0.1:7676.

Backends should point to local servers when developing locally. Avoid proxying to remote production origins to prevent accidentally leaking request data.

Quick Start

# Install Viceroy cargo install --locked viceroy # Build your Compute app fastly compute build # Start local server (default: 127.0.0.1:7676) viceroy -C fastly.toml bin/main.wasm # Or use the Fastly CLI wrapper fastly compute serve

References

Topic

File

Use when...

Serve

fastly-compute-serve.md

Starting local dev server, profiling, advanced server options

Config

fastly-compute-config.md

Configuring fastly.toml backends, stores, geolocation, device detection, ACLs

Test

fastly-compute-test.md

Running Rust unit tests with cargo-nextest, writing tests for Compute services

Adapt

fastly-compute-adapt.md

Converting core WASM modules to Component Model, custom build pipelines

Viceroy — Local Fastly Compute Runtime

Viceroy is Fastly's official local testing environment for Compute applications. It emulates the Fastly Compute platform, allowing you to develop and test WASM services locally.

Viceroy documentation: https://github.com/fastly/Viceroy

Common Gotchas

Dictionaries and ConfigStores are both supported but configured differently in fastly.toml. Dictionaries go under [local_server.dictionaries] as inline key-value maps or JSON files. ConfigStores go under [local_server.config_stores].
fastly.toml must have a [local_server] section. Without it, Viceroy won't know about your backends, stores, or other local overrides. Every backend your app calls must be listed under [local_server.backends].
Default port is 7676, not 5000 (which is Fastlike's default). Access your app at http://127.0.0.1:7676.
Backends should point to local servers when developing locally. Avoid proxying to remote production origins to prevent accidentally leaking request data.

Quick Start

# Install Viceroy
cargo install --locked viceroy

# Build your Compute app
fastly compute build

# Start local server (default: 127.0.0.1:7676)
viceroy -C fastly.toml bin/main.wasm

# Or use the Fastly CLI wrapper
fastly compute serve

References

Topic	File	Use when...
Serve	fastly-compute-serve.md	Starting local dev server, profiling, advanced server options
Config	fastly-compute-config.md	Configuring fastly.toml backends, stores, geolocation, device detection, ACLs
Test	fastly-compute-test.md	Running Rust unit tests with cargo-nextest, writing tests for Compute services
Adapt	fastly-compute-adapt.md	Converting core WASM modules to Component Model, custom build pipelines