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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, and rust. 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.