Abdul WahabandCursor
35ae07339b
Grok was classified as GitHub Copilot, so the design hook skipped every edit with no-file-path and never ran Stop. Normalize toolInput/sessionId and treat Stop additionalContext as the Grok product. Prepared with AI assistance. Co-authored-by: Cursor <cursoragent@cursor.com>
12 KiB
Harness Skills Capabilities Reference
Source of truth for what each AI coding harness supports in terms of agent skills.
Used to inform provider configs in scripts/lib/transformers/providers.js.
Last verified: 2026-04-28 (subagent landscape spot-checked 2026-06-28; Mistral Vibe row verified 2026-07-16; Grok Build skills row verified 2026-07-21; Grok Build hook stdin captured 2026-08-24)
This file is point-in-time. Capabilities move fast; verify live before relying on any "only X supports Y" claim. Notably, the subagent table below lists Impeccable's emission targets, not the support landscape (see its note).
Official Documentation
| Harness | Docs URL |
|---|---|
| Claude Code | https://code.claude.com/docs/en/skills |
| Cursor | https://cursor.com/docs/context/skills |
| Gemini CLI | https://geminicli.com/docs/cli/skills/ |
| Codex CLI | https://developers.openai.com/codex/skills |
| GitHub Copilot (Agents) | https://code.visualstudio.com/docs/copilot/customization/agent-skills |
| Kiro | https://kiro.dev/docs/skills/ |
| OpenCode | https://opencode.ai/docs/skills/ |
| Pi | https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/docs/skills.md |
| Qoder | https://docs.qoder.com/extensions/skills |
| Trae | TBD (no official skills docs found yet) |
| Rovo Dev | https://support.atlassian.com/rovo/docs/extend-rovo-dev-cli-with-agent-skills |
| Mistral Vibe | https://docs.mistral.ai/vibe/code/cli/skills |
| Grok Build | https://docs.x.ai/build/features/skills-plugins-marketplaces |
| Hermes Agent | https://hermes-agent.nousresearch.com/docs/ |
| Antigravity | https://antigravity.google/docs/skills |
Spec Compliance
All harnesses follow the Agent Skills specification to varying degrees. The spec defines these frontmatter fields: name, description, license, compatibility, metadata, allowed-tools.
Provider-specific extensions beyond the spec: user-invocable, argument-hint, disable-model-invocation, allowed-tools (extended syntax), model, effort, context, agent, hooks, subtask, mcp.
Frontmatter Support
Fields marked with * are spec-standard. Others are provider extensions.
| Field | Claude Code | Cursor | Gemini | Codex | Copilot | Grok | Hermes | Kiro | OpenCode | Pi | Qoder | Rovo Dev | Mistral Vibe | Antigravity |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
name* |
Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
description* |
Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
license* |
Yes | Yes | Ignored | No | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
compatibility* |
Yes | Yes | Ignored | No | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
metadata* |
Yes | Yes | Ignored | No | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
allowed-tools* |
Yes | No | Ignored | No | No | Yes | No | No | Yes | Yes | Yes | Yes | Yes | Yes |
user-invocable |
Yes | No | No | No | Yes | Yes | No | No | Yes | No | Yes | Yes | Yes | No |
argument-hint |
Yes | No | No | No | Yes | Yes | No | No | Yes | No | Yes | Yes | No | No |
disable-model-invocation |
Yes | Yes | No | No | Yes | Yes | No | No | Yes | Yes | TBD | TBD | No | No |
model |
Yes | No | No | No | No | Yes | No | No | Yes | No | No | No | No | No |
effort |
Yes | No | No | No | No | Yes | No | No | No | No | No | No | No | No |
context |
Yes | No | No | No | No | No | No | No | No | No | No | No | No | No |
agent |
Yes | No | No | No | No | No | No | No | Yes | No | No | No | No | No |
hooks |
Yes | No | No | Yes | No | Yes | No | No | No | No | No | No | No | No |
Notes:
- Gemini CLI validates only
nameanddescription; other spec fields are parsed but ignored. - Codex CLI uses a separate
agents/openai.yamlsidecar for skill metadata (icons, branding, MCP tools, invocation control). Codex also auto-discovers subagents bundled inside an installed skill'sagents/folder (TOML), which is how Impeccable ships its asset-producer. Standalone custom agents can still live under.codex/agents/or~/.codex/agents/, but Impeccable no longer installs anything there. - Codex CLI hooks ship under
[features].hooks = true(still flagged), require/hookstrust ceremony per-update, and are disabled on Windows. - Grok Build is Claude Code compatible with zero config: it also reads
.claude/skills/,.claude/settings.jsonhooks, and Claude plugin layouts. Native paths are.grok/skills/,.grok/hooks/*.json, and.grok/agents/. Skill frontmatter supportswhen-to-usein addition to the fields above. Project hooks require/hooks-trust(or--trust). See https://docs.x.ai/build/features/skills-plugins-marketplaces and https://docs.x.ai/build/features/hooks. - Hermes Agent reads the Agent Skills spec as-is. Spec-defined fields (
name,description,license,compatibility,metadata) are parsed and stored; harness-specific extensions (user-invocable,argument-hint,allowed-tools,disable-model-invocation,model,effort,context,agent,hooks) are unknown keys and silently ignored. Hermes has no hook surface, no per-skill tool ACL, and no slash-command equivalent ofuser-invocable(skills are loaded via/skill <name>or auto-loaded; sub-commands like/impeccable polishare routed from the skill body, not declared in frontmatter). Hermes adds two frontmatter fields not in the spec:platforms:(OS filter; default = all) andenvironments:(relevance gate overkanban,docker,s6). Unknown fields are silently ignored. - Kiro recognizes
user-invocableanddisable-model-invocationper community reports but does not formally document them. - Antigravity supports standard Agent Skills spec frontmatter fields (
name,description,license,compatibility,metadata,allowed-tools). - Unknown fields are silently ignored by all harnesses.
Hook surface used by Impeccable
| Harness | Edit hook | Startup hook | Manifest location | Notes |
|---|---|---|---|---|
| Claude Code | Yes (PostToolUse) |
No | .claude/settings.json |
Project-local settings entry installed by npx impeccable skills install/update. Runs .claude/skills/impeccable/scripts/hook.mjs. |
| Codex CLI | Yes (PostToolUse) |
No | .codex/hooks.json |
Project-local manifest installed with the .agents/skills/impeccable payload. Runs .agents/skills/impeccable/scripts/hook.mjs from the git root. Requires normal /hooks trust approval. |
| Cursor | Yes (preToolUse) |
No | .cursor/hooks.json |
Project-level manifest installed with .cursor/skills/impeccable. Runs hook-before-edit.mjs to block bad proposed writes before they land. Reloads on save; restart Cursor if hooks do not pick up. |
| Grok Build | Yes (PostToolUse) |
No | .grok/hooks/impeccable.json |
Project-local manifest installed with .grok/skills/impeccable. Claude-compatible matchers (Edit|Write|MultiEdit) alias to Grok search_replace. PostToolUse runs the scan and warms the session cache; Grok ignores that stdout. Stop additionalContext is the user-visible pass. Ignore Grok's observe-only Stop with reason: "shutdown". Requires /hooks-trust or --trust. Plugin installs use plugin/hooks/hooks.json with ${CLAUDE_PLUGIN_ROOT} (aliased to GROK_PLUGIN_ROOT). |
| All other harnesses | No | No | n/a | No documented hook surface today. Skill and commands still ship. |
Skill Directory Structure
| Harness | Native directory | Also reads |
|---|---|---|
| Claude Code | .claude/skills/ |
- |
| Cursor | .cursor/skills/ |
.agents/skills/, .claude/skills/ |
| Gemini CLI | .gemini/skills/ |
.agents/skills/ |
| Codex CLI | .agents/skills/ (primary) |
- |
| GitHub Copilot | .github/skills/ |
.agents/skills/, .claude/skills/ |
| Kiro | .kiro/skills/ |
- |
| OpenCode | .opencode/skills/ |
.agents/skills/, .claude/skills/ |
| Pi | .pi/skills/ (project), ~/.pi/agent/skills/ (global) |
.agents/skills/ |
| Qoder | .qoder/skills/ |
~/.qoder/skills/ (user-level) |
| Trae China | .trae-cn/skills/ |
TBD |
| Trae International | .trae/skills/ |
TBD |
| Rovo Dev | .rovodev/skills/ |
~/.rovodev/skills/ (user-level) |
| Mistral Vibe | .vibe/skills/ (project), ~/.vibe/skills/ (global) |
.agents/skills/ (project), ~/.agents/skills/ (global) |
| Grok Build | .grok/skills/ (project), ~/.grok/skills/ (global) |
.agents/skills/, .claude/skills/, .cursor/skills/ (Claude/Cursor compat, configurable) |
| Hermes Agent | .hermes/skills/ (project), ~/.hermes/skills/ (global) |
skills.external_dirs config (no automatic .agents/skills/ fallback) |
| Antigravity | .agent/skills/ (project), ~/.gemini/config/skills/ (global) |
.agents/skills/ (project), ~/.agents/skills/ (global) |
All harnesses support the {skill-name}/SKILL.md directory structure with optional reference/, scripts/, and assets/ subdirectories.
Native Subagent Directory Structure (Impeccable emission targets)
Scope: this table is where Impeccable emits native subagent files, not a map of which harnesses support subagents. Subagents are broadly supported now: Cursor (auto-delegation +
/nameinvocation, https://cursor.com/docs/subagents), GitHub Copilot, and Google Antigravity ship them too. Impeccable only writes native files where there is a stable, documented on-disk format to target.
| Harness | Native directory | File format |
|---|---|---|
| Claude Code | .claude/agents/ (installed plugin) |
Markdown with YAML frontmatter |
| Grok Build | .grok/agents/ (project) and plugin agents/ |
Markdown with YAML frontmatter (Claude-compatible) |
| Codex CLI | <skill>/agents/ (nested, auto-discovered) |
TOML |
Impeccable keeps canonical agent prompts under skill/agents/ and emits provider-native files only for harnesses with a documented on-disk subagent format. Claude reads its agents from the installed plugin; Grok reads the same markdown agents from the plugin package and from project .grok/agents/; Codex auto-discovers the TOML bundled inside the installed skill's own agents/ folder, so the normal skills install carries it with no separate sidecar.
Spawn / permission model (matters more than directory support when building skills):
| Harness | Who can spawn a subagent |
|---|---|
| Claude Code | Programmatically, from within the skill/agent flow. |
| Grok Build | Programmatically via spawn_subagent (built-in types plus project/user agents under .grok/agents/). |
| Codex CLI | Only if the user has allowed sub-agents / parallel work; otherwise the skill must ask once, then stop (see skill/reference/critique.md <codex> gate). |
| Cursor | Agent-chosen: auto-delegated by the Agent, or user-invoked via /name. Not reliably skill-spawnable. |
| Others | Varies; treat as unavailable unless verified, and degrade loudly. |
Placeholder / Variable Substitution
Claude Code supports runtime variable substitution directly in SKILL.md bodies: $ARGUMENTS, $0-$N, ${CLAUDE_SKILL_DIR}, ${CLAUDE_SESSION_ID}. No other harness supports substitution in skills.
Some harnesses have separate "custom commands" systems (distinct from skills) with their own substitution:
| Harness | Command system | Substitution syntax |
|---|---|---|
| Gemini CLI | .gemini/commands/ (TOML) |
{{args}}, !{shell}, @{file} |
| Codex CLI | .codex/prompts/ |
$ARGNAME |
| OpenCode | .opencode/commands/ |
$ARGUMENTS, $1-$N, !`shell` |
Our build system handles cross-provider placeholders at compile time via replacePlaceholders() for {{model}}, {{config_file}}, {{ask_instruction}}, and {{available_commands}}.