> ## Documentation Index > Fetch the complete documentation index at: https://site.aspect.build/llms.txt > Use this file to discover all available pages before exploring further. # BUILD File Generation with aspect gazelle > Generate and sync Bazel BUILD files automatically with aspect gazelle: incremental runs for monorepo scale, drift detection in CI, and custom Gazelle extensions in Starlark. export const MarketingPage = () =>
; export const CTA = ({title, subtitle, primaryCta, primaryHref = "#", secondaryCta, secondaryHref = "#"}) =>

{title}

{subtitle &&
{subtitle}
}
{primaryCta && {primaryCta} } {secondaryCta && {secondaryCta} }
; export const FeatureCard = ({title, description, href, children}) => { const Tag = href ? "a" : "div"; const tagProps = href ? { href } : {}; return {children &&
{children}
}

{title}

{description &&

{description}

} ; }; export const FeatureGrid2 = ({children}) =>
{children}
; export const FeatureGrid3 = ({children}) =>
{children}
; export const SectionHeader = ({title, subtitle, centered = true, label}) =>
{label &&

{label}

}

{title}

{subtitle &&
{subtitle}
}
; export const Section = ({children, className = "", gray = false, dark = false, id}) =>
{children}
; export const Hero = ({title, subtitle, badge, primaryCta, primaryHref = "#", secondaryCta, secondaryHref = "#", centered = true, children}) =>
{centered && !children ?
{badge &&
{badge}
}

{String(title).split(/\\n|\n/).map((line, i) => i ? [
, line] : line)}

{subtitle &&
{subtitle}
}
{primaryCta && {primaryCta} } {secondaryCta && {secondaryCta} }
:
{badge &&
{badge}
}

{String(title).split(/\\n|\n/).map((line, i) => i ? [
, line] : line)}

{subtitle &&
{subtitle}
}
{primaryCta && {primaryCta} } {secondaryCta && {secondaryCta} }
{children &&
{children}
}
}
;

Writing BUILD files by hand requires every engineer to learn Bazel's configuration language, and hand-written files drift out of sync the moment someone adds an import and forgets the dep.

Your source code already declares its dependencies. BUILD files should be generated from it, checked in CI, and fixed with one command.

The aspect gazelle task

Drift fails CI. Fixes apply themselves.

The aspect gazelle task runs Gazelle over your repository and adapts to where it runs. In CI it detects whether BUILD files are out of sync with source code and fails the step if so, preventing drift before it accumulates into a bigger cleanup. On a developer machine, the same command applies the fixes in place.

One Gazelle invocation produces both the verdict and the patch, so even the CI check stays fast on a large monorepo.

```shell theme={null} # On a laptop: writes the fixes in place aspect gazelle # In CI: fails the job if BUILD files are out of sync aspect gazelle --check-only ```

The aspect-gazelle open source project

Extensions in Starlark, not Go

Gazelle is the standard tool for generating BUILD files, but extending it means learning its Go API and adding a compile-time dependency for your developers. With the Aspect Extension Language (AXL), you write Gazelle extensions in Starlark instead: declare the rule kinds you generate, tell Gazelle what to look for in source files, and write the logic that produces targets.

Extensions are short, live in your repo next to the code they generate for, and need no compilation. They run on aspect-gazelle, our open source Gazelle distribution: prebuilt binaries bundling the language plugins and the Starlark extension host, plus quality-of-life upgrades stock Gazelle lacks, like gitignore support, file-based caching, and a watch mode powered by Watchman. The aspect gazelle task runs it for you; you can also run it standalone.

```python title="oci_image.axl" theme={null} def declare_targets(ctx): for file in ctx.sources: if len(file.query_results["has_main"]) > 0: ctx.targets.add( name = "image", kind = "go_image", attrs = { "binary": path.base(ctx.rel), }, ) ```
Python JavaScript & TypeScript Go Protobuf C & C++ Starlark