Custom agent file reference

Ask in VS Code

This article describes custom agent file syntax, frontmatter fields, and harness-specific configuration in VS Code. For creation steps, file locations, and a complete starter example, see Create and manage custom agents.

File structure

A custom agent file contains an optional YAML header, enclosed by --- delimiters, followed by a Markdown body with the agent's instructions:

---
name: Reviewer
description: Review changes without editing files
tools: ['read', 'search']
---
Review the supplied changes for correctness and missing tests.
Report actionable findings with file references. Do not edit files.

The fields below describe the VS Code format. Files in .claude/agents use the Claude agent format.

Harness compatibility

The selected agent harness determines which fields and tool names take effect. A shared file location does not imply identical behavior across harnesses.

Local supports the VS Code tool names, subagent configuration, handoffs, and agent-scoped hooks described below.
Copilot supports custom agent configuration through its runtime. Use the field-specific guidance below and the Copilot custom agent documentation. Local handoffs do not apply. Agent-scoped hooks have a current plugin-agent conversion limitation.
Claude uses its own agent format and runtime behavior.
Copilot cloud agent has a separate configuration reference. The target: github-copilot value refers to that target, not the Copilot harness selected in VS Code.

Header fields

All fields in this table are optional. Defaults and harness-specific behavior are listed where applicable.

Field	Type	Description
`name`	String	The agent's name in the UI. Defaults to the file name.
`description`	String	What the agent does and when to use it.
`argument-hint`	String	Hint text that describes the input the agent expects. Shown in the Local chat input.
`tools`	String or array of strings	Tools available to the agent. Tool names and supported aliases depend on the harness. User-defined tool sets are deprecated and are not supported in the Copilot harness. See Tools.
`agents`	Array of strings	Custom agents available as subagents. In Local, use `['*']` or omit the field to allow all available agents, or use `[]` to prevent subagent use. Include the `agent` tool set in `tools`. See Subagent configuration.
`model`	String or array of strings	The model to use in the Copilot harness. An array specifies models in preference order, using the first available model. If omitted, the currently selected model is used. Local subagents also use this field as part of their model selection order.
`reasoning-effort`	String	Reasoning effort for the agent in the Copilot harness: `low`, `medium`, `high`, `xhigh`, or `max`. Availability depends on the selected model. See Thinking effort.
`user-invocable`	Boolean	Whether the agent appears in the agents dropdown in Local and Copilot. Defaults to `true`. Set to `false` to hide a subagent-only helper from the picker.
`disable-model-invocation`	Boolean	Whether to prevent other agents from invoking this agent as a subagent. Defaults to `false`. See Subagent configuration for the Local explicit-list exception.
`infer`	Boolean	Deprecated. Use `user-invocable` and `disable-model-invocation` to control picker visibility and subagent invocation separately.
`target`	String	The target environment for the file: `vscode` or `github-copilot`. This is not the harness selector.
`mcp-servers`	Object	MCP server configurations for custom agents in Copilot cloud agent. Not used by custom agents in VS Code.
`handoffs`	Array of objects	Suggested transitions to another agent after a response in Local. See Handoff fields.
`hooks`	Object	Hook event map scoped to this agent. The Copilot harness supports agent-scoped hooks, but VS Code currently omits this field when converting plugin-provided agents. Retain the definition and leave the affected migration incomplete. See the conversion limitation. Local execution requires chat.useHooks Open in VS Code Open in VS Code Insiders and a trusted workspace.

Tools

In Local, tools can include built-in tools, MCP tools, and tools contributed by extensions. Existing user-defined tool-set references are deprecated and are not supported in the Copilot harness. See Replace tool sets. Built-in aliases such as read and search are separate from user-defined tool-set files. To include all tools from an MCP server, use <server name>/*.

tools: ['read', 'search', '<server name>/*']

Replace <server name> with the name of a configured MCP server. If tools is omitted in Local, the tools enabled in the tools picker are available. Unavailable tools are ignored.

For Copilot and other harnesses, check tool availability before reusing a Local agent's tool list.

Model preferences

To specify a prioritized list, replace the placeholders with model names available in your harness:

model: ['<preferred model>', '<fallback model>']

Subagent configuration

In Local, restrict a coordinator to named workers by combining agents with the agent tool set:

tools: ['agent']
agents: ['Researcher', 'Implementer']

Agent names are case-sensitive. Explicitly listing an agent in agents permits invocation even if that worker sets disable-model-invocation: true. To allow a subagent to delegate further, enable chat.subagents.allowInvocationsFromSubagents Open in VS Code Open in VS Code Insiders . This also applies to an agent that lists itself. See Nested subagents.

For complete coordinator and worker files, see Delegate implementation to a worker.

Visibility and invocation

To hide an agent from the picker while keeping it available for delegation:

user-invocable: false
disable-model-invocation: false

These fields change the shared agent definition, not a personal visibility preference. See Customize the agents dropdown list.

Handoff fields

Each object in the handoffs array defines a transition in the Local harness:

Field	Type	Description
`label`	String, required	Text on the handoff button.
`agent`	String, required	The target agent identifier.
`prompt`	String, required	The prompt to pre-fill when the user selects the handoff.
`send`	Boolean	Whether to submit the prompt automatically. Defaults to `false`.
`model`	String	Model to select for the handoff. Use the qualified name in the format `<model name> (<vendor>)`, such as `<model name> (copilot)`.

handoffs:
  - label: Implement Plan
    agent: agent
    prompt: Implement the plan outlined above.
    send: false
    model: <model name> (copilot)

Replace the model placeholder with an available model, or omit model. For a planning-to-implementation walkthrough, see Handoffs.

Body

The Markdown body contains the instructions the agent follows, such as its task, guidelines, and expected output.

Reference files with Markdown links or #file: syntax. Relative paths resolve from the custom agent file. Use ~ or ~/ to reference your home folder, and use Unix-style / separators to keep paths portable across operating systems.

Follow the [review checklist](./review-checklist.md).
Use #file:~/copilot/security-guidelines.md for security reviews.

In Local, reference a tool with #tool:<tool-name>, such as #tool:web/fetch.

When you select the custom agent in the Chat view, its body instructions are added after your custom instructions and take precedence if they conflict.

Tool list priority

In Local, a prompt file's tools list takes precedence over the custom agent's tools list. Other harnesses don't load prompt files. For the full order, see Tool list priority.

Claude agent format

Agent files in .claude/agents use plain .md files and the Claude subagents format.

Field	Description
`name`	Required unique agent identifier using lowercase letters and hyphens.
`description`	Required description of when to delegate to the agent.
`tools`	Comma-separated allowed tool names, such as `"Read, Grep, Glob, Bash"`. If omitted, the agent inherits all tools.
`disallowedTools`	Comma-separated tool names to block.
`model`	`sonnet`, `opus`, `haiku`, or `inherit` (default).
`permissionMode`	`default`, `acceptEdits`, `dontAsk`, `bypassPermissions`, or `plan`.
`skills`	Skills to load into the agent's context at startup.
`mcpServers`	MCP servers available to the agent.
`hooks`	Lifecycle hooks scoped to the agent.
`memory`	Persistent memory scope: `user`, `project`, or `local`.

The Claude harness implements these fields according to its provider documentation. When Local loads a Claude-format agent, it maps supported Claude tool and model names to their VS Code equivalents. This compatibility does not make all Claude runtime features available in Local.

Related resources

10/21/2026

Sunbelt Computer Software

PL/B Language Development and Support