| name | harness-subagent |
| description | Create and manage subagent entities in the agent-harness workspace. Invoke this skill when a user wants to define, scaffold, apply, or remove a subagent across Claude Code, OpenAI Codex, or GitHub Copilot. |
/harness-subagent
Use this skill to create and manage subagent entities in the agent-harness workspace. A subagent is a specialized agent definition — with a name, description, optional tool restrictions, and an optional model override — that harness renders into provider-native agent configuration files for every enabled provider.
What is a subagent entity?
A subagent entity is a single canonical Markdown source file under .harness/src/subagents/<subagent-id>.md. It contains:
- Required YAML frontmatter:
name and description
- Optional frontmatter: provider-specific fields set via override sidecars (model, tools, handoffs)
- Body: Markdown prose that becomes the agent's system prompt
Harness renders one output artifact per enabled provider from that single source file. You edit the source once; all provider files stay in sync.
Provider output mapping
Claude Code
| Item | Value |
|---|
| Output path | .claude/agents/<subagent-id>.md |
| Format | Markdown with YAML frontmatter |
| Required frontmatter | name, description |
| Optional frontmatter | tools (string or string[]), model |
Claude Code loads agent files from .claude/agents/ at session start. Each file's description field tells Claude when to delegate to that agent. Claude routes tasks automatically, or the user can invoke an agent explicitly with @agent-<name> or the /agents command. Supported model values: sonnet, opus, haiku, a full model ID such as claude-sonnet-4-6, or inherit (default). Subagents run in isolated context windows and cannot spawn further subagents.
Official docs: https://code.claude.com/docs/en/sub-agents
OpenAI Codex CLI
| Item | Value |
|---|
| Output path | .codex/config.toml |
| Format | TOML, section [agents.<subagent-id>] |
| Required fields | description, developer_instructions (body) |
| Optional fields | model, model_reasoning_effort, nickname_candidates |
Harness writes all enabled subagents into .codex/config.toml under [agents.<id>] entries. The description drives when Codex routes to that agent role; the body becomes developer_instructions. Codex also supports standalone TOML agent files in .codex/agents/ (outside of harness management), which are auto-discovered and take precedence over same-named inline entries.
Official docs: https://developers.openai.com/codex/config-reference
GitHub Copilot
| Item | Value |
|---|
| Output path | .github/agents/<subagent-id>.agent.md |
| Format | Markdown with YAML frontmatter |
| Required frontmatter | description |
| Optional frontmatter | name, tools (string[]), model, handoffs, mcp-servers, target, disable-model-invocation, user-invocable |
Copilot discovers agent files in .github/agents/ at the repository level. The handoffs field is Copilot-specific and is supported in VS Code agent mode: it defines routing buttons that let users switch to another agent mid-conversation, optionally with a pre-filled prompt. Note: handoffs are currently not supported by the Copilot coding agent on GitHub.com — they are silently ignored there. Example handoff entry (VS Code only):
handoffs:
- label: "Start Implementation"
agent: implementation
prompt: "Now implement the plan outlined above."
send: true
When send: true is set, the handoff prompt submits automatically.
Official docs: https://docs.github.com/en/copilot/reference/custom-agents-configuration
Cursor
| Item | Value |
|---|
| Output path | .cursor/agents/<subagent-id>.md |
| Format | Markdown with YAML frontmatter |
| Required frontmatter | name, description |
| Optional frontmatter | model, readonly, is_background |
Cursor loads agent files from .cursor/agents/ (project) or ~/.cursor/agents/ (user). For compatibility, it also scans .claude/agents/ and .codex/agents/ (project-level) and their user-level equivalents. Project subagents take precedence when names conflict; .cursor/ takes precedence over .claude/ or .codex/.
The description field determines when the agent delegates to a subagent. Subagents can be invoked explicitly via /name syntax or automatically based on task complexity. The model field supports fast, inherit (default), or a specific model ID. When readonly: true, the subagent runs with restricted write permissions.
Cursor includes three built-in subagents (explore, bash, browser) that run automatically. Custom subagents cannot spawn further subagents (single-level only).
Official docs: https://docs.cursor.com/agent/subagents
Provider-specific frontmatter comparison
| Field | Claude Code | Codex CLI | GitHub Copilot | Cursor |
|---|
name | required | via TOML key | optional | required |
description | required | required | required | required |
tools | string or string[] | — | string[] | — |
model | optional | optional | optional | optional (fast, inherit, or model ID) |
readonly | — | — | — | optional (boolean) |
is_background | — | — | — | optional (boolean) |
developer_instructions | — | required (body) | — | — |
handoffs | — | — | optional (VS Code only) | — |
Provider-specific options (model, tools, handoffs) are set through override sidecar files, not in the canonical source frontmatter — see the Override sidecars section below.
Canonical source format
---
name: <human-readable display name>
description: <when this agent should be used — used by all providers>
---
You are a [role description]. When invoked:
1. [Step one]
2. [Step two]
3. [Step three]
Focus on [specific domain]. Do not [out-of-scope actions].
Only name and description are required in the canonical frontmatter. The body becomes the agent's system prompt for all providers.
Override sidecars
To set provider-specific options (model, tools, handoffs), create or edit the generated override YAML files:
.harness/src/subagents/<subagent-id>.overrides.claude.yaml.harness/src/subagents/<subagent-id>.overrides.codex.yaml.harness/src/subagents/<subagent-id>.overrides.copilot.yaml
Example Claude override sidecar:
version: 1
options:
model: haiku
tools:
- Read
- Grep
- Glob
Example Copilot override sidecar:
version: 1
options:
model: gpt-4o
tools:
- search
- fetch
handoffs:
- label: "Hand off to planner"
agent: planner
prompt: "Now create a plan based on the research above."
Harness CLI commands
npx harness add subagent <subagent-id>
npx harness plan
npx harness apply
npx harness watch
npx harness remove subagent <subagent-id>
npx harness remove subagent <subagent-id> --no-delete-source
Complete example
Source file: .harness/src/subagents/code-reviewer.md
---
name: code-reviewer
description: Expert code review specialist. Reviews code for quality, security, and maintainability. Use proactively after writing or modifying code.
---
You are a senior code reviewer ensuring high standards of quality and security.
When invoked:
1. Run git diff to see recent changes
2. Focus on modified files
3. Begin review immediately without asking for clarification
Review checklist:
- Code is clear and readable
- Functions and variables are well-named
- No duplicated logic
- Proper error handling and input validation
- No exposed secrets or API keys
- Adequate test coverage
- Performance considerations addressed
Provide feedback organized by priority:
- Critical issues (must fix before merging)
- Warnings (should fix)
- Suggestions (consider improving)
Include specific examples of how to fix each issue. Do not modify files yourself.
Override sidecar for Claude (.harness/src/subagents/code-reviewer.overrides.claude.yaml):
version: 1
options:
model: sonnet
tools:
- Read
- Grep
- Glob
- Bash
After running npx harness apply, this produces:
.claude/agents/code-reviewer.md — used by Claude Code- An entry in
.codex/config.toml under [agents.code-reviewer] — used by Codex
.github/agents/code-reviewer.agent.md — used by GitHub Copilot
Typical workflow
npx harness add subagent code-reviewer
npx harness plan
npx harness apply
Check .claude/agents/, .codex/config.toml, and .github/agents/ to verify the rendered output.
References
