Testing and debugging Fastly services with Fiddle

WARNING: Fiddle is a Fastly Labs experimental project, not a Fastly product. See Fastly Labs terms of use for more details.

The Fastly Fiddle tool allows you to create VCL-based, ephemeral Fastly services without logging into a Fastly account, and provides detailed instrumentation of how your requests and responses are handled by Fastly.

The Fiddle web interface

Learn more about Fiddle in the sections below:

The Fiddle philosophy

Many services offer similar tools under names like fiddle, pen, bin or playground. Examples include JS Fiddle, Codepen, Rust playground, and Regexr. The principle of a fiddle tool is to hide all or most setup and orchestration tasks, allowing you to focus on code immediately, and to save your work automatically, publicly, and on a unique, sharable permalink.

Fiddle is typically useful when you want to try out a Fastly feature before signing up, debug a problem with your Fastly service, or share solution code with friends or colleagues.

Access, write-protection and cloning

By default, fiddles are OPEN. When you share an open fiddle, the recipient will be able to edit it in exactly the same way that you can, and their edits may conflict with yours if you are editing at the same time. There is no locking or attempt to synchronize simultaneous edits. Nevertheless, the OPEN status is useful if you are collaborating on a fiddle, or submitting a test case to Fastly support.

If you prefer to lock your fiddle, so that only you can edit it, choose Lock from the menu in the upper right of the screen. Remember that your fiddle is still visible to the whole world, but now only you can edit it. Others will see a Clone option to enable them to create their own version.

We recommend locking fiddles most of the time, as it will prevent unexpected conflicting edits, and cloning a fiddle is easy and free. If you want to freeze a fiddle permanently, so that no-one can edit it, including you, choose Freeze from the menu. You and anyone else can still see it, run it and clone it, but no-one can edit it.

Example fiddles

See the recipes in our solutions library for a wide selection of service configuration ideas expressed as fiddles.

User contributed notes

We welcome comments that add use cases, ideas, tips, and caveats. All comments will be moderated before publication. To post support questions, visit our support center and we'll find you the help you need.