# Capability Manifest Reference (`capability.json`)

> **Canonical ADRs:** [ADR-1244](../adr/1244-capability-ecosystem.md) · [ADR-894](../adr/894-capability-declaration-format.md) · [ADR-1016](../adr/1016-runtime-capability-descriptor.md)
> **See also:** [How to develop a capability](../how-to/develop-a-capability.md) · [Capability Command Reference](gsd-capability-command.md)

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"`).

---

## 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 | Yes | Short human-readable label. Must be a non-empty string. |
| `description` | string | Yes | Longer summary sentence. Must be a non-empty string. |
| `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[] | Yes | Capability `id` values this capability depends on. Must be present as an array (use `[]` when there are no dependencies). Each entry 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. |
| `runtimeCompat` | object | Yes (`role: "feature"`) | Declares which host runtimes this capability can surface through. Validated for every `role: "feature"` capability (a feature manifest without it fails validation). Sub-fields: `supported` — a **non-empty** array of kebab-case runtime ids, or the single wildcard `["*"]` for a runtime-agnostic capability; `unsupported` — an array of kebab-case runtime ids (the wildcard is **not** permitted here); `notes` — optional object mapping a runtime id (or `"*"`) to a non-empty explanatory string. The wildcard `"*"` may not be mixed with concrete ids in the same array, and the reserved names `__proto__`/`constructor`/`prototype` are rejected. |
| `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. |

---

## 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. The hook `command` written into the host settings is the realpath-confined **absolute** path to this script (so it always runs the bundle's own file regardless of the working directory) and is POSIX single-quoted (so an install prefix containing spaces cannot break it). For shell safety the path must contain only `[A-Za-z0-9._/-]` — no whitespace, no shell metacharacters (`; \| & $ ` `` ` `` `( ) < > * ? [ ] { } ! ~ # ' " \` newline), no leading `-`, no absolute path, and no `..` segment. A script outside this allowlist fails validation and the capability is rejected. |

### `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 | Required | Description |
|---|---|---|---|
| `point` | string | Yes | One of the 12 valid loop extension point identifiers (see table below). |
| `ref` | object | Yes | The dispatch target. Exactly one of `{ "skill": "<stem>" }`, `{ "agent": "<stem>" }`, or `{ "command": "<name>" }` (the three are mutually exclusive). A `skill`/`agent` stem must be declared in this capability's `skills`/`agents` array. |
| `produces` | string[] | Yes | Artefact names this step produces. Must be present as an array (use `[]` when it produces none); an omitted `produces` fails validation. No two capability steps may produce the same artefact at the same point. |
| `consumes` | string[] | Yes | Artefact names this step consumes. Must be present as an array (use `[]` when it consumes none); an omitted `consumes` fails validation. |
| `onError` | `"skip"` \| `"halt"` | Yes | Behaviour on failure; must be present and one of `"skip"` or `"halt"` (an omitted `onError` fails validation). Steps are purely additive — they never halt or redirect the host workflow on their own; a blocking precondition is expressed as a `gate`. |
| `when` | string | No | 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. |
| `fragment` | object | No | Optional inline-or-file prompt fragment attached to the step, with the **same** `{ "path": "<relative path>" }` or `{ "inline": "<string>" }` semantics as a contribution's `fragment`. A `path` is materialised (read and inlined) at load time, resolved against the capability directory and confined to it (`..` traversal is rejected). |

### `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 | Required | Description |
|---|---|---|---|
| `point` | string | Yes | One of the 12 valid loop extension point identifiers. |
| `into` | string | Yes | Agent role name. Must be a role published by that loop extension point in the host contract. |
| `produces` | string[] | Yes | Artefact names this contribution produces. Use `[]` when it produces none. |
| `consumes` | string[] | Yes | Artefact names this contribution reads. Use `[]` when it reads none. |
| `fragment` | object | Yes | Either `{ "path": "<relative path>" }` (file content) or `{ "inline": "<string>" }` (literal text). |
| `when` | string | No | Dotted config key; activates the contribution conditionally. |
| `onError` | `"skip"` \| `"halt"` | No | Behaviour on failure. |

### `gates`

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

| Sub-field | Type | Required | Description |
|---|---|---|---|
| `point` | string | Yes | One of the 12 valid loop extension point identifiers. |
| `check` | object | Yes | One of three forms (see table below). Must be present as an object; an omitted `check` fails validation. |
| `blocking` | boolean | Yes | Must be present and a boolean; an omitted `blocking` fails validation. When `true`, a failed check halts the loop at this point. |
| `onError` | `"skip"` \| `"halt"` | Yes | Behaviour when the check itself errors; must be present and one of `"skip"` or `"halt"` (an omitted `onError` fails validation). |
| `when` | string | No | Dotted config key; activates the gate conditionally. |

**`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. |

---

## 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 |

---

## 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](../adr/1016-runtime-capability-descriptor.md).

| 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`. `probeExists` is an optional sub-path applied to probe candidates: for `generic-agents-root` it is a hard filter (a candidate qualifies only if `<candidate>/<probeExists>` exists); for `dot-home-nested` it is a preference that makes probing pick the candidate GSD owns (e.g. `gsd-core/VERSION`) over a bare-existing sibling before falling back — see ADR-1016 and #213/#217. |
| Local config dir | `runtime.localConfigDir` | Required dot-prefixed string. The runtime's **local** content-rewrite directory — the `./` target GSD stamps into rewritten artefact bodies (e.g. `./.claude/` → `./<localConfigDir>/`) and the local install dir basename. Backs `getDirName()` (registry-derived, #1679). Usually `.<runtime>` (the runtime's home dot-dir), but **three runtimes diverge** because they read GSD's content from a non-home directory: `copilot` → `.github` (GitHub Copilot reads custom instructions from `.github/copilot-instructions.md` / `.github/instructions/`; see `convertClaudeToCopilotContent` rewrites in `src/runtime-artifact-conversion.cts`), `antigravity` → `.agents` (local agent/workflow dir; see the antigravity rewrites in `src/runtime-artifact-conversion.cts`), `kimi` → `.kimi-code`. Distinct from `configHome.name` (the **global** install home, which for these three is `.copilot` / `antigravity` / `agents`). Byte-parity-proven against the prior hand-maintained mapping by the golden-install-parity harness. |
| 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](../adr/1016-runtime-capability-descriptor.md).

---

## 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.

---

## Example — complete `role: "feature"` capability

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

```json
{
  "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" },
  "runtimeCompat": { "supported": ["*"], "unsupported": [] },
  "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", "produces": [], "consumes": [], "fragment": { "path": "loop/threat-model.md" }, "when": "workflow.security_enforcement" }` (`produces` and `consumes` are required arrays — use `[]` when empty).