Feather

Effortlessly add a command shell to your application: for your users, and your agents.

Try It Live

Use It

GitHub

Embeddable

Designed from the ground up to be embedded into host applications. No I/O, no event loop - your host stays in control.

Inspectable

Every aspect of a running Feather program can be inspected and modified from within, perfect for debugging and agentic coding.

TCL-Compatible

A faithful implementation of the TCL core language with control flow, data structures, metaprogramming, and string manipulation.

Interactive Playground

Try Feather directly in your browser - powered by WebAssembly

Feather Script

Canvas

What Feather is a good fit for

Feather is built for short, interactive programs:

Give agents access to your program - like Chrome DevTools, but for your application
Configure servers at runtime - hot-reload configuration without restarts
Quake-style consoles - add developer consoles to games and applications
Configuration file format - use a real programming language for config
User customization - let users script and extend your software

Just like Bash and zsh let you drive a Unix system, Feather lets you drive your application in the same spirit.

When to use something else

Feather is not suited for programming in the large.

Features that support this are omitted intentionally:

No I/O by default: Feather cannot communicate with the outside world, until you explicitly provide facilities for doing so.

No packaging/import system: if your Feather program grows large, you need to decide whether you move this logic to the host, or provide the means of structuring code, like sourcing scripts from somewhere yourself.

Performance will never be the top priority: Feather is there to let you elegantly call code in your probably already optimized host application. A Feather script becoming slow is a sign that you need to move logic to the host application.

If you need large scale, performant programming in an embeddable programming language, you are looking for Lua.

Feather is lightweight glue

Feather is designed to be embedded into a host language.

The core implementation provides the language semantics, but all memory allocations, I/O, Unicode and floating point operations are provided by the host.

Chances are that if you are embedding a scripting language in 2025, your host language already has an implementation of everything and duplicating Unicode tables or getting two event loops to play nice with each other is more trouble than it's worth.

Feather provides libraries for using Feather directly in your programming language.