Skip to main contentThe aspect command-line interface supercharges your terminal experience. It enhances Bazel’s build and query functionalities, enabling seamless integration with the Developer Workflows your team relies on. Unlike ad-hoc shell scripts, it provides a robust and intuitive abstraction that aligns perfectly with Bazel’s design principles.
You can find the source code, report issues, and download the latest releases at the Aspect CLI GitHub repository.
Aspect extension language
The Aspect Extension Language (AXL) is a specialized dialect of Starlark designed to configure and extend the Aspect CLI.
Just as Bazel uses .bzl files to define Starlark-based configurations with Bazel’s built-in library, the Aspect CLI employs .axl files to create and manage its extensions. This parallel ensures a seamless transition for developers familiar with Bazel’s ecosystem while leveraging the power of Aspect’s specialized tooling.
AXL takes inspiration from the Buck Extension Language (BXL) and tools like Tilt, both of which leverage Starlark as their configuration language. By adopting this approach, AXL provides a consistent, intuitive experience for developers familiar with Starlark-based ecosystems, while introducing enhancements tailored to Aspect’s unique capabilities.
Watch Alex’s BazelCon 2025 talk for a quick overview of the extension language and why we made it:
Task extensions
This AXL interface enables you to define custom commands for the aspect CLI, extending its capabilities to suit your specific workflows. The same extensible library implements built-in commands, ensuring consistency and ease of use.
Gazelle extensions
The AXL interface enhances Bazel’s BUILD file generator by allowing you to incorporate custom business logic written in Starlark.
For an in-depth guide on creating these extensions, check out the Aspect 301 training course.
API reference
Explore the full API documentation to dive deeper into the available methods, properties, and examples for leveraging AXL in your projects. 
