AGENTS/skill/agent-development/SKILL.md

name, description, compatibility

name	description	compatibility
agent-development	(opencode - Skill) Create and configure agents for Opencode. Use when: (1) creating a new agent, (2) adding agents to agents.json or opencode.json, (3) configuring agent permissions, (4) setting up primary vs subagent modes, (5) writing agent system prompts, (6) understanding agent triggering. Triggers: create agent, add agent, agents.json, subagent, primary agent, agent permissions, agent configuration, agent prompt.	opencode

Agent Development for Opencode

Overview

Agents are specialized AI assistants configured for specific tasks and workflows. Opencode supports two agent types with different configuration formats.

Agent Types

Type	Description	Invocation
Primary	Main assistants for direct interaction	Tab key to cycle, or configured keybind
Subagent	Specialized assistants for delegated tasks	Automatically by primary agents, or @ mention

Built-in agents:

• build (primary) - Full development with all tools enabled
• plan (primary) - Analysis/planning with edit/bash requiring approval
• general (subagent) - Multi-step tasks with full tool access
• explore (subagent) - Fast, read-only codebase exploration

Configuration Formats

Agents can be defined in two formats. Ask the user which format they prefer; default to JSON if no preference stated.

Format 1: JSON (recommended for central management)

• In opencode.json under the agent key
• Or standalone agents.json file
• Best for: version control, Nix flake consumption, central configuration

Format 2: Markdown (for quick addition)

• Global: ~/.config/opencode/agents/*.md
• Per-project: .opencode/agents/*.md
• Best for: project-specific agents, quick prototyping

JSON Agent Structure

In opencode.json

{
  "$schema": "https://opencode.ai/config.json",
  "agent": {
    "agent-name": {
      "description": "When to use this agent",
      "mode": "primary",
      "model": "provider/model-id",
      "prompt": "{file:./prompts/agent-name.txt}",
      "permission": { ... },
      "tools": { ... }
    }
  }
}

Standalone agents.json

{
  "agent-name": {
    "description": "When to use this agent",
    "mode": "subagent",
    "model": "anthropic/claude-sonnet-4-20250514",
    "prompt": "You are an expert...",
    "tools": {
      "write": false,
      "edit": false
    }
  }
}

Markdown Agent Structure

File: ~/.config/opencode/agents/agent-name.md or .opencode/agents/agent-name.md

---
description: When to use this agent
mode: subagent
model: anthropic/claude-sonnet-4-20250514
temperature: 0.1
tools:
  write: false
  edit: false
  bash: false
permission:
  bash:
    "*": ask
    "git diff": allow
---

You are an expert [role]...

**Your Core Responsibilities:**
1. [Responsibility 1]
2. [Responsibility 2]

The filename becomes the agent name (e.g., review.md → review agent).

Configuration Options

description (required)

Defines when Opencode should use this agent. Critical for subagent triggering.

"description": "Reviews code for best practices and security issues"

mode

Controls how the agent can be used.

Value	Behavior
primary	Directly accessible via Tab cycling
subagent	Invoked by Task tool or @ mention
all	Both (default if omitted)

"mode": "primary"

model

Override the model for this agent. Format: provider/model-id.

"model": "anthropic/claude-sonnet-4-20250514"

If omitted: primary agents use globally configured model; subagents inherit from invoking primary agent.

prompt

System prompt defining agent behavior. Can be inline or file reference.

Inline:

"prompt": "You are an expert code reviewer..."

File reference:

"prompt": "{file:./prompts/agent-name.txt}"

File paths are relative to the config file location.

temperature

Control response randomness (0.0 - 1.0).

Range	Use Case
0.0-0.2	Focused, deterministic (code analysis, planning)
0.3-0.5	Balanced (general development)
0.6-1.0	Creative (brainstorming)

"temperature": 0.1

maxSteps

Limit agentic iterations before forcing text-only response.

"maxSteps": 10

tools

Control which tools are available. Boolean to enable/disable, or object for granular control.

Disable specific tools:

"tools": {
  "write": false,
  "edit": false,
  "bash": false
}

Wildcard for MCP tools:

"tools": {
  "mymcp_*": false
}

hidden

Hide subagent from @ autocomplete menu. Agent can still be invoked via Task tool.

"hidden": true

disable

Disable the agent entirely.

"disable": true

Permissions System

Permissions control what actions require approval. Each rule resolves to:

• "allow" - Run without approval
• "ask" - Prompt for approval
• "deny" - Block the action

Permission Types

Permission	Matches Against
read	File path
edit	File path (covers edit, write, patch, multiedit)
bash	Parsed command
task	Subagent type
external_directory	Paths outside project
doom_loop	Repeated identical tool calls

Simple Permissions

"permission": {
  "edit": "ask",
  "bash": "ask"
}

Granular Permissions with Glob Patterns

Rules evaluated in order; last matching rule wins.

"permission": {
  "read": {
    "*": "allow",
    "*.env": "deny",
    "*.env.*": "deny",
    "*.env.example": "allow"
  },
  "bash": {
    "*": "ask",
    "git status*": "allow",
    "git log*": "allow",
    "git diff*": "allow",
    "rm *": "ask",
    "sudo *": "deny"
  },
  "edit": "allow",
  "external_directory": "ask",
  "doom_loop": "ask"
}

Task Permissions (Subagent Control)

Control which subagents an agent can invoke via Task tool.

"permission": {
  "task": {
    "*": "deny",
    "code-reviewer": "allow",
    "test-generator": "ask"
  }
}

Complete JSON Example

{
  "chiron": {
    "description": "Personal AI assistant (Plan Mode). Read-only analysis and planning.",
    "mode": "primary",
    "model": "anthropic/claude-sonnet-4-20250514",
    "prompt": "{file:./prompts/chiron.txt}",
    "permission": {
      "read": {
        "*": "allow",
        "*.env": "deny",
        "*.env.*": "deny",
        "*.env.example": "allow",
        "*/.ssh/*": "deny",
        "*credentials*": "deny"
      },
      "edit": "ask",
      "bash": "ask",
      "external_directory": "ask"
    }
  },
  "chiron-forge": {
    "description": "Personal AI assistant (Worker Mode). Full write access.",
    "mode": "primary",
    "model": "anthropic/claude-sonnet-4-20250514",
    "prompt": "{file:./prompts/chiron-forge.txt}",
    "permission": {
      "read": {
        "*": "allow",
        "*.env": "deny"
      },
      "edit": "allow",
      "bash": {
        "*": "allow",
        "rm *": "ask",
        "git push *": "ask",
        "sudo *": "deny"
      }
    }
  },
  "code-reviewer": {
    "description": "Reviews code for quality, security, and best practices",
    "mode": "subagent",
    "model": "anthropic/claude-sonnet-4-20250514",
    "temperature": 0.1,
    "tools": {
      "write": false,
      "edit": false
    },
    "prompt": "You are an expert code reviewer..."
  }
}

System Prompt Design

Write prompts in second person, addressing the agent directly.

Standard Structure

You are [role] specializing in [domain].

**Your Core Responsibilities:**
1. [Primary responsibility]
2. [Secondary responsibility]
3. [Additional responsibilities]

**Process:**
1. [Step one]
2. [Step two]
3. [Continue with clear steps]

**Quality Standards:**
- [Standard 1]
- [Standard 2]

**Output Format:**
[What to include and how to structure]

**Edge Cases:**
- [Edge case 1]: [How to handle]
- [Edge case 2]: [How to handle]

Prompt File Convention

Store prompts in a prompts/ directory with .txt extension:

• prompts/agent-name.txt

Reference in config:

"prompt": "{file:./prompts/agent-name.txt}"

Best Practices

DO:

• Use second person ("You are...", "You will...")
• Be specific about responsibilities
• Provide step-by-step processes
• Define output format
• Include quality standards
• Address edge cases
• Keep under 10,000 characters

DON'T:

• Write in first person
• Be vague or generic
• Omit process steps
• Leave output format undefined

Creating Agents

Method 1: Opencode CLI (Interactive)

opencode agent create

Prompts for: location, description, tools, then generates the agent file.

Method 2: JSON Configuration

1. Add agent to opencode.json or agents.json
2. Create prompt file in prompts/ directory
3. Validate with scripts/validate-agent.sh

Method 3: Markdown File

1. Create ~/.config/opencode/agents/agent-name.md or .opencode/agents/agent-name.md
2. Add frontmatter with configuration
3. Write system prompt as markdown body

Validation

Validate agent configuration:

# Validate agents.json
./scripts/validate-agent.sh agents.json

# Validate markdown agent
./scripts/validate-agent.sh ~/.config/opencode/agents/review.md

Testing

1. Reload opencode or start new session
2. For primary agents: use Tab to cycle
3. For subagents: use @ mention or let primary agent invoke via Task tool
4. Verify expected behavior and tool access

Quick Reference

JSON Agent Template

{
  "my-agent": {
    "description": "What this agent does and when to use it",
    "mode": "subagent",
    "model": "anthropic/claude-sonnet-4-20250514",
    "prompt": "{file:./prompts/my-agent.txt}",
    "tools": {
      "write": false,
      "edit": false
    }
  }
}

Markdown Agent Template

---
description: What this agent does and when to use it
mode: subagent
model: anthropic/claude-sonnet-4-20250514
tools:
  write: false
  edit: false
---

You are an expert [role]...

Configuration Options Summary

Option	Required	Type	Default
description	Yes	string	-
mode	No	primary/subagent/all	all
model	No	string	inherited
prompt	No	string	-
temperature	No	number	model default
maxSteps	No	number	unlimited
tools	No	object/boolean	all enabled
permission	No	object	allow
hidden	No	boolean	false
disable	No	boolean	false

Additional Resources

• System prompt patterns: See references/system-prompt-design.md
• Triggering examples: See references/triggering-examples.md
• AI-assisted generation: See examples/agent-creation-prompt.md
• Complete examples: See examples/complete-agent-examples.md
• Real-world JSON example: See references/opencode-agents-json-example.md