Welcome to the Fastly reference library. Here you'll find comprehensive technical detail about the interfaces exposed by the Fastly platform and products, including complete syntax and examples for functions, variables, CLI commands, and API endpoints.
Our VCL platform evolved from Varnish 2.1.5 and supports a heavily modified and extended variant of Varnish Configuration Language (VCL) for programming custom, high performance edge logic on our VCL services.
Our Compute platform runs WebAssembly binaries compiled from your own code. Find out more about our official SDKs, environment variables and more.
Via the Fastly API you can perform any of the operations that are possible within the management console, including creating services, domains, and backends, configuring rules or uploading your own application code, as well as account operations such as user administration and billing reports.
Use the Fastly CLI to manage services, scaffold out local development environments and compile your Compute projects, among a host of other useful features.
The Fastly Image Optimizer (IO) allows images to be transformed, resized, and optimized on the fly as they move through the Fastly edge cloud. Use IO query parameters to control the behavior of the optimizer.
Fastly respects standards in our implementations of HTTP, but in some cases there are nuances in our implementation, or extensions to the standards.