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A stack is a reusable language-runtime definition — the Dockerfile steps that provision a toolchain like Node.js, Go, Python, or Rust. Declaring a stack installs it in your project’s shared base image, before your own build instructions run, so root_run/user_run steps can rely on it.

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Selecting stacks

List the stacks your build needs under build.stacks:
build.stacks is a whole-value selection: the highest config layer that sets it wins, so a project can replace the list a user-level config provides. Each entry is a component name — bare for a built-in or loose stack, or a qualified namespace.bundle.component address for a bundled stack:
Stacks are self-guarding — each skips itself when the image already provides its runtime — so declaring one is always safe. See Image Customization for how stacks fit into the two-stage build, per-harness stack overlays, and build ordering.

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Where stacks come from

A stack name resolves across the same three tiers as every component. A bare name resolves in precedence order — your user convention directory, then the project convention directory, then the built-in floor — stopping at the first match. A qualified name resolves from an installed bundle. See where components come from for the canonical resolution model.

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Built-in stacks

Clawker ships node, go, python, rust, java, ruby, cpp, and dotnet. They resolve by bare name with no declaration beyond listing them in build.stacks, and update with the clawker binary.

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Loose local stacks

Drop a stack directory into a convention directory and it exists immediately — no install, no manifest wrapper, bare-named:
A loose stack in the user directory shadows a project one of the same name, which shadows a built-in — and a shadow is always visible in clawker stack list. This is how you customize a built-in stack: copy its source into a convention directory and edit it there.

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Bundled stacks

A stack shipped in a bundle is addressed by its qualified name (namespace.bundle.component) and becomes available once the bundle is declared and installed. See Bundles.

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Authoring a stack

Writing your own stack — the stack.yaml manifest and the Dockerfile fragments that accompany it — is covered in Authoring stacks.