msd-core/docs/reference/capability-manifest.md

Capability Manifest Reference (capability.json)

Canonical ADRs: ADR-1244 · ADR-894 · ADR-1016 See also: How to develop a capability · Capability Command Reference

Each capability is a folder capabilities/<id>/ (or an overlay root ~/.gsd/capabilities/<id>/ / .gsd/capabilities/<id>/) containing one capability.json declaration. The file is schema-validated JSON with a common envelope plus a role-typed body (role: "feature" or role: "runtime").

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Envelope fields

These fields are present for both role: "feature" and role: "runtime" capabilities.

Field	Type	Required	Description
id	string (kebab-case)	Yes	Unique identifier; must equal the folder name. The prefix gsd-, gsd-core-, and anthropic- are reserved for first-party use.
role	"feature" | "runtime"	Yes	Discriminator that selects the body schema.
version	semver string	Yes (1.6.0+)	Semantic version of this capability. The registry rejects a manifest without one.
title	string	No	Short human-readable label.
description	string	No	Longer summary sentence.
tier	"core" | "standard" | "full"	Yes	Source of truth for install-profile membership and surface cluster assignment. tier propagates via the requires-closure; install profiles are generated from it.
requires	string[]	No	Capability id values this capability depends on. Must exist in the registry, be acyclic, and be tier-monotone (a core capability may not require a standard or full capability; a standard capability may not require a full capability).
engines	object	No	Host-compatibility constraint. Sub-field: gsd — semver range string (e.g. ">=1.6.0 <3.0.0"). Acts as a hard gate at install and at load; a mismatch blocks installation and causes the overlay to be skipped with a warning at load time.
compatVersions	object	No	Graceful-downgrade table mapping "<capVersion>" to "<min gsd version>". Only meaningful for sources that enumerate versions (git tags, registry, npm); a bare tarball URL carries one version and simply blocks on incompatibility.
integrity	string	No	sha512-<base64> hash of the capability bundle. Verified before extraction when present; mismatch aborts install.
provenance	object	No	{ sourceRepo: string, commit: string }. Emitted in CI for first-party and curated capabilities.
author	object	No	{ name: string, email?: string, url?: string }.
homepage	string	No	URL.
repository	string	No	URL.
license	string	No	SPDX licence identifier (e.g. "MIT").
keywords	string[]	No	Arbitrary search tags.

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Feature body (role: "feature")

Feature capabilities declare owned artefacts, lifecycle hooks, a federated configuration slice, and loop extension registrations.

skills and agents

Sub-field	Type	Description
skills	string[]	Owned skill stems. Exactly one capability may own each stem across the entire merged registry (first-party ∪ overlay).
agents	string[]	Owned agent stems. Same uniqueness constraint as skills.

hooks

Non-loop lifecycle hooks.

Sub-field	Type	Description
event	string	Hook event name (host-runtime specific).
script	string	Path to the hook script, relative to the capability root.

config — federated config-key schema slice

The config field is an object whose keys are federated configuration keys contributed by this capability. Each key must be absent from the central config-schema and absent from every other capability's config object (collision fails the build gate). Each entry has the following shape:

Property	Type	Description
type	"boolean" | "string" | "number" | "enum"	Value type.
default	(type-consistent)	Default value; must be consistent with type.
description	string	Human-readable explanation of the key's effect.
values	string[]	enum only. Exhaustive list of permitted string values.

steps

Steps run at a loop extension point as independent units. Ordering within a point is derived from produces/consumes (topological sort; capability-id is the tiebreak).

Sub-field	Type	Description
point	string	One of the 12 valid loop extension point identifiers (see table below).
ref	object	Either { "skill": "<stem>" } or { "agent": "<stem>" }.
produces	string[]	Artefact names this step produces. No two capability steps may produce the same artefact at the same point.
consumes	string[]	Artefact names this step consumes.
when	string	Dotted config key; the step is active only when the key is truthy. Evaluated deterministically at render time; phase-context applicability is the skill's own responsibility.
onError	"skip" | "halt"	Behaviour on failure. "skip" is the default. Steps are purely additive — they never halt or redirect the host workflow on their own; a blocking precondition is expressed as a gate.

contributions

Contributions inject a fragment into a named agent role's prompt at a loop extension point. Multiple contributions into the same agent role render as ordered labelled blocks (<contribution from="<id>">…</contribution>).

Sub-field	Type	Description
point	string	One of the 12 valid loop extension point identifiers.
into	string	Agent role name. Must be a role published by that loop extension point in the host contract.
fragment	object	Either { "path": "<relative path>" } (file content) or { "inline": "<string>" } (literal text).
when	string	Dotted config key; activates the contribution conditionally.
onError	"skip" | "halt"	Behaviour on failure.

gates

Gates check a condition at a loop extension point and optionally block progression.

Sub-field	Type	Description
point	string	One of the 12 valid loop extension point identifiers.
check	object	One of three forms (see table below).
when	string	Dotted config key; activates the gate conditionally.
blocking	boolean	When true, a failed check halts the loop at this point.
onError	"skip" | "halt"	Behaviour when the check itself errors.

check forms:

Form	Shape	Blocking permitted	Notes
Query	{ "query": "<gsd_run query>" }	Yes	Deterministic first-party code.
Predicate	{ "predicate": { "kind": "artifact-exists" | "config-equals" | …, … } }	Yes	Declarative; no code path.
Agent verdict	{ "agentVerdict": { "ref": …, "prompt": … } }	No (forced advisory)	LLM evaluation; non-deterministic checks may not halt the loop.

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Valid point values

The 12 loop extension points are a closed, additive-only vocabulary. Every steps, contributions, and gates entry must use one of these identifiers exactly.

Point	Phase	Position
discuss:pre	Discuss	Before the discuss step executes
discuss:post	Discuss	After the discuss step completes
plan:pre	Plan	Before the plan step executes
plan:post	Plan	After the plan step completes
execute:pre	Execute	Before the execute phase begins
execute:wave:pre	Execute	Before each execution wave
execute:wave:post	Execute	After each execution wave
execute:post	Execute	After the execute phase completes
verify:pre	Verify	Before the verify step executes
verify:post	Verify	After the verify step completes
ship:pre	Ship	Before the ship step executes
ship:post	Ship	After the ship step completes

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Runtime body (role: "runtime")

Runtime capabilities describe how GSD projects its artefacts onto one host CLI. The body is a closed 8-axis (plus 4 install-surface) vocabulary; no feature-only fields (skills, agents, steps, contributions, gates, hooks) are permitted. Full semantic specifications, the closed enum values for each axis, and the 16-runtime worked examples are in ADR-1016.

Axis	Field	Type summary
Config home	runtime.configHome	Structured object with kind (dot-home | dot-home-nested | xdg | generic-agents-root), name, optional parent, env[], probe[], probeExists, skillsHome.
Config format	runtime.configFormat	Closed enum: settings-json | toml | markdown | markdown-dir | none.
Artefact layout	runtime.artifactLayout	Object with global and local arrays of ArtifactKind (kind, destSubpath, prefix, nesting, recursive, stage).
Command style	runtime.commandStyle	Closed enum: slash-hyphen | shell-var.
Hooks surface	runtime.hooksSurface	Closed enum: settings-json | codex-hooks-json | cursor-hooks-json | copilot-inline | cline-rules | none.
Sandbox tier	runtime.sandboxTier	Closed enum: none | codex-agent-sandbox.
Support tier	runtime.supportTier	Integer: 1 (fully tested first-party) | 2 (shipped, lower coverage).
Install surface	runtime.installSurface	Closed enum: settings-json | codex-toml | copilot-instructions | cline-rules | cursor-hooks-json | profile-marker-only.
Shared settings	runtime.writesSharedSettings	boolean. Whether the runtime writes a shared settings.json.
Permission writer	runtime.permissionWriter	null | "opencode" | "kilo". The finish-time permissions-sidecar writer.
Extended hook events	runtime.extendedHookEvents	string[] over a closed vocabulary: SubagentStop, Stop, PreCompact, FileChanged, BeforeAgent, AfterAgent, BeforeModel.

For a minimal role: "runtime" example, see ADR-1016 §Decision 8.

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Conformance invariants

The following invariants are enforced at build time by scripts/gen-capability-registry.cjs and at install time by the runtime-callable validateCapability() / validateCrossCapability() over the merged first-party ∪ overlay set.

• version is required. The registry rejects any manifest without a semver version field.
• id uniqueness. No two capabilities may share an id. An overlay whose id collides with a first-party id is rejected; first-party always wins.
• Skill and agent stem uniqueness. Exactly one capability may own each skill or agent stem across the entire merged registry.
• requires exist and are acyclic. Every id listed in requires must exist in the registry; the dependency graph must be acyclic.
• requires is tier-monotone. A core capability may not require a standard or full capability. A standard capability may not require a full capability.
• point values are from the closed set. Every point in steps, contributions, and gates must be one of the 12 identifiers above.
• contribution.into is a published agent role. The into value must be an agent role declared by the host contract for that loop extension point.
• Config key exclusivity. A federated config key must be owned by exactly one capability and absent from the central config-schema. Presence in both is a collision; a half-migrated key fails the build gate.
• Artefact production uniqueness per point. No two capability steps may produces the same artefact name at the same loop extension point.
• engines.gsd is a hard gate. A capability whose engines.gsd range does not satisfy the installed GSD version is blocked at install and skipped (with a warning) at load time.
• Path confinement. Declared module paths may not use parent-directory traversal (../); modules are require()'d only from the capability's own install root.
• Reserved namespace. Capability id values beginning with gsd-, gsd-core-, or anthropic- are reserved; third-party capabilities using these prefixes are rejected.

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Example — complete role: "feature" capability

The following is the canonical UI design-contract capability from ADR-894. It illustrates all major body sections.

{
  "id": "ui",
  "role": "feature",
  "version": "1.0.0",
  "title": "UI design contracts",
  "description": "UI-SPEC design contract and retrospective UI audit for frontend phases.",
  "tier": "standard",
  "requires": [],
  "engines": { "gsd": ">=1.6.0" },
  "skills": ["ui-phase", "ui-review"],
  "agents": ["gsd-ui-checker", "gsd-ui-auditor"],
  "hooks": [],
  "config": {
    "workflow.ui_phase": {
      "type": "boolean",
      "default": true,
      "description": "Enable the UI design-contract gate during planning."
    },
    "workflow.ui_review": {
      "type": "boolean",
      "default": true,
      "description": "Enable the retrospective UI audit."
    },
    "workflow.ui_safety_gate": {
      "type": "boolean",
      "default": true,
      "description": "Block execution on unmet UI-SPEC contracts."
    }
  },
  "steps": [
    {
      "point": "plan:pre",
      "ref": { "skill": "ui-phase" },
      "produces": ["UI-SPEC.md"],
      "consumes": ["CONTEXT.md"],
      "when": "workflow.ui_phase",
      "onError": "skip"
    },
    {
      "point": "verify:post",
      "ref": { "skill": "ui-review" },
      "produces": ["UI-REVIEW.md"],
      "consumes": ["UI-SPEC.md"],
      "when": "workflow.ui_review",
      "onError": "skip"
    }
  ],
  "contributions": [],
  "gates": [
    {
      "point": "execute:wave:post",
      "check": { "query": "ui.safety-gate" },
      "when": "workflow.ui_safety_gate",
      "blocking": true,
      "onError": "halt"
    }
  ]
}

Notes on this example:

• when on each hook references its own config key; whether the phase is actually a frontend phase is decided inside ui-phase (self-gate).
• The plan:pre step self-skips on non-frontend phases, producing no UI-SPEC.md; the execute:wave:post gate's ui.safety-gate query passes gracefully when no UI-SPEC.md exists.
• A contribution follows this shape: { "point": "plan:pre", "into": "planner", "fragment": { "path": "loop/threat-model.md" }, "when": "workflow.security_enforcement" }.