Create a2a mcp

/create-a2a-mcp — Scaffold MCP Servers for A2A Agents

Trigger phrases: "create MCP", "scaffold MCP server", "add MCP to agent", "create-a2a-mcp", "/create-a2a-mcp" Works standalone AND as an integration hook from /create-a2a.

Purpose

Scaffold a complete, production-ready MCP (Model Context Protocol) server surface for any A2A agent or standalone project. Generates all required files, registers in opencode.json, and validates the result.

When to Use

Scenario	How
Building a new A2A agent	/create-a2a calls this skill automatically after base scaffold
Adding MCP to an existing agent	Call this skill directly on the agent root
Creating a standalone MCP server	Call this skill with a target directory

What Gets Scaffolded

<agent-root>/
├── src/mcp-server.ts          # MCP server with registerTool() pattern
├── mcp-config.json            # MCP config for local consumers
├── clients/opencode-mcp.json  # OpenCode client config
└── (cli.ts patched)           # serve-mcp command added if missing

Plus optionally:

• Global registration in ~/.config/opencode/opencode.json
• Bin wrapper at /Users/jeremy/dev/SIN-Solver/bin/sin-<slug>

SSOT Paths

Asset	Path
Template MCP server	/Users/jeremy/dev/SIN-Solver/a2a/template-repo/A2A-SIN-Agent-Template/src/mcp-server.ts
Template mcp-config	/Users/jeremy/dev/SIN-Solver/a2a/template-repo/A2A-SIN-Agent-Template/mcp-config.json
Template client config	/Users/jeremy/dev/SIN-Solver/a2a/template-repo/A2A-SIN-Agent-Template/clients/opencode-mcp.json
Template CLI	/Users/jeremy/dev/SIN-Solver/a2a/template-repo/A2A-SIN-Agent-Template/src/cli.ts
Global opencode config	/Users/jeremy/.config/opencode/opencode.json
SIN-Solver bin dir	/Users/jeremy/dev/SIN-Solver/bin/
Shared lib	scripts/_mcp-lib.mjs (this skill)

Built-in Scripts

Script	Purpose	Usage
scripts/_mcp-lib.mjs	Shared helpers (arg parsing, slug normalization, file I/O)	Imported by other scripts
scripts/mcp-scaffold.mjs	Generate all MCP files from tool definitions	node mcp-scaffold.mjs --agent-root <path> --slug <name> --tools '<json>'
scripts/mcp-register-global.mjs	Register MCP in global opencode.json	node mcp-register-global.mjs --slug <name> --agent-root <path> [--bin-wrapper]
scripts/mcp-verify.mjs	Validate MCP setup completeness	node mcp-verify.mjs --agent-root <path> --slug <name>

Workflow

Step 0 — Gather Input

Collect from user or from /create-a2a handoff:

Parameter	Required	Description
agent-root	✅	Absolute path to agent/project root
slug	✅	MCP slug (e.g. sin-research, sin-server)
namespace	❌	Tool namespace prefix (defaults to slug with - → _)
tools	❌	JSON array of tool definitions (see format below)
register-global	❌	Register in opencode.json (default: true)
bin-wrapper	❌	Create bin wrapper in SIN-Solver/bin/ (default: false)
env-vars	❌	JSON object of environment variables for MCP config

Step 1 — Run Scaffold

SCRIPTS=~/.config/opencode/skills/create-a2a-mcp/scripts
node $SCRIPTS/mcp-scaffold.mjs \
  --agent-root /path/to/agent \
  --slug sin-myagent \
  --tools '[{"name":"do_thing","description":"Does a thing","params":{"input":"string"},"action":"myagent.do_thing"}]'

This generates:

• src/mcp-server.ts — Full MCP server with all tools registered via McpServer.registerTool()
• mcp-config.json — Local MCP config
• clients/opencode-mcp.json — OpenCode client config
• Patches src/cli.ts to include serve-mcp command if missing

Step 2 — Register Globally (Optional)

node $SCRIPTS/mcp-register-global.mjs \
  --slug sin-myagent \
  --agent-root /path/to/agent \
  --bin-wrapper

Step 3 — Verify

node $SCRIPTS/mcp-verify.mjs \
  --agent-root /path/to/agent \
  --slug sin-myagent

Expected output: all checks green.

Step 4 — Build & Smoke Test

npm --prefix <agent-root> run build
echo '{}' | node <agent-root>/dist/src/cli.js serve-mcp
# Should start without errors and respond to MCP protocol

Tool Definition Format

Each tool in the --tools JSON array:

{
  "name": "do_thing",
  "description": "Does a specific thing",
  "params": {
    "input": "string",
    "count": "number?",
    "confirm": "boolean?"
  },
  "action": "myagent.do_thing"
}

Type mapping:

• string → z.string() (required)
• string? → z.string().optional() (optional)
• number → z.number() (required)
• number? → z.number().optional() (optional)
• boolean → z.boolean() (required)
• boolean? → z.boolean().optional() (optional)
• array → z.array(z.string()) (required)
• array? → z.array(z.string()).optional() (optional)

Default Tools (Always Generated)

Every MCP server gets these baseline tools automatically:

1. <namespace>_help — Describe available agent actions
2. <namespace>_health — Check base agent readiness
3. <namespace>_onboarding_status — Read onboarding state
4. <namespace>_onboarding_save — Persist onboarding state (requires confirm=true)

Integration with /create-a2a

When called from /create-a2a, the handoff contract is:

{
  "agent-root": "/absolute/path/to/agent",
  "slug": "sin-agentname",
  "namespace": "sin_agentname",
  "tools": [...],
  "register-global": true,
  "bin-wrapper": true,
  "env-vars": { "KEY": "value" }
}

The /create-a2a SKILL.md should include this step after base scaffold:

### MCP Surface Generation
After scaffolding the base agent, invoke skill `create-a2a-mcp` to generate the MCP server surface.
Pass the agent-root, slug, and domain-specific tool definitions.

MCP Server Pattern Reference

Production Pattern (McpServer.registerTool — PREFERRED)

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { z } from 'zod';

const server = new McpServer({ name: 'sin-myagent', version: '0.1.0' });

server.registerTool('sin_myagent_help',
  { description: 'Describe available actions.' },
  async () => ({
    content: [{ type: 'text', text: JSON.stringify(result, null, 2) }],
  })
);

const transport = new StdioServerTransport();
await server.connect(transport);

Transport Modes

Mode	When	Config
stdio	Local agents, opencode CLI	Default. Always use for A2A agents.
streamable-http	Remote/cloud agents	Only if agent runs on remote VM
SSE	Legacy	DEPRECATED. Never use for new agents.

Anti-Patterns

❌ Template name drift — always replace template-a2a-sin-agent with actual slug ❌ Missing serve-mcp in CLI — breaks opencode integration ❌ Business logic in mcp-server.ts — keep it thin, delegate to runtime.ts ❌ Hardcoded paths in mcp-config.json — use relative paths for portability ❌ SSE transport for new projects — use stdio or streamable-http ❌ Shared mutable server state across clients — fresh handler per call

Checklist

• src/mcp-server.ts exists with all tools registered
• mcp-config.json exists with correct slug
• clients/opencode-mcp.json exists with correct slug
• src/cli.ts has serve-mcp command
• No template name drift (no template-a2a-sin-agent references)
• Global opencode.json registration (if requested)
• Bin wrapper created (if requested)
• npm run build succeeds
• serve-mcp starts without errors
• All default tools respond (help, health, onboarding)

Related Skills

• See Skill Catalog for related skills