MCP Builder

name: arcanea-mcp-builder description: Guide for building MCP (Model Context Protocol) servers for the Arcanea ecosystem. Use when creating new MCP tools, extending packages/arcanea-mcp, adding Arcanea-branded tools, integrating external APIs as MCP endpoints, or building new MCP servers for the Arcanea AI toolkit. Triggers on: MCP server, MCP tool, model context protocol, mcp-builder, create tool, arcanea-mcp, new MCP. Sourced from Anthropic's official mcp-builder skill, adapted for Arcanea's TypeScript + Bun stack. license: MIT (source: anthropics/skills/mcp-builder) metadata: author: Arcanea (adapted from Anthropic) version: "1.0.0" stack: TypeScript strict, Bun, MCP TypeScript SDK, Hono

Arcanea MCP Builder

"Shinkami guards the Source Gate at 1111 Hz — Meta-consciousness. MCP tools are the hands through which meta-consciousness acts. Build them with clarity and precision."

Adapted from Anthropic's official MCP builder guide for the Arcanea ecosystem. Arcanea MCP servers live in packages/arcanea-mcp/.

Architecture Overview

packages/arcanea-mcp/
├── src/
│   ├── index.ts              # Server entry point
│   ├── tools/                # Tool definitions (one file per domain)
│   │   ├── guardian-tools.ts
│   │   ├── lore-tools.ts
│   │   ├── prompt-tools.ts
│   │   └── academy-tools.ts
│   ├── skills/               # Skill rules engine (existing)
│   │   ├── skill-rules-engine.ts
│   │   └── feedback-bridge.ts
│   └── resources/            # MCP resources (read-only data)
│       └── canon-resource.ts
└── package.json

Phase 1: Plan the MCP Server

Define Tool Scope

Before writing code, answer:

1. What does this tool enable the AI to do? (action-oriented, not data-oriented)
2. What's the minimal set of tools? (prefer comprehensive coverage over abstractions)
3. What auth does it need? (Supabase JWT, API keys, or none)
4. What should error messages say? (actionable, guide toward solution)

Tool Naming Convention (Arcanea)

arcanea_{domain}_{verb}_{noun}
arcanea_lore_get_guardian
arcanea_lore_search_texts
arcanea_academy_unlock_gate
arcanea_prompts_create
arcanea_prompts_list
arcanea_canon_validate

Phase 2: Implement with TypeScript SDK

Setup

cd packages/arcanea-mcp
# Already in monorepo — add SDK if needed
bun add @modelcontextprotocol/sdk zod

Server Entry Point

// packages/arcanea-mcp/src/index.ts
import { Server } from '@modelcontextprotocol/sdk/server/index.js'
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'
import { registerGuardianTools } from './tools/guardian-tools.js'
import { registerLoreTools } from './tools/lore-tools.js'
import { registerAcademyTools } from './tools/academy-tools.js'

const server = new Server(
  {
    name: 'arcanea-mcp',
    version: '1.0.0',
  },
  {
    capabilities: { tools: {} },
  }
)

// Register all tool groups
registerGuardianTools(server)
registerLoreTools(server)
registerAcademyTools(server)

// Start with stdio transport (for Claude Code integration)
const transport = new StdioServerTransport()
await server.connect(transport)

Tool Definition Pattern

// packages/arcanea-mcp/src/tools/guardian-tools.ts
import { Server } from '@modelcontextprotocol/sdk/server/index.js'
import {
  CallToolRequestSchema,
  ListToolsRequestSchema,
} from '@modelcontextprotocol/sdk/types.js'
import { z } from 'zod'
import { supabaseAdmin } from '../lib/supabase-admin.js'

const GetGuardianSchema = z.object({
  gate: z.enum([
    'foundation', 'flow', 'fire', 'heart', 'voice',
    'sight', 'crown', 'shift', 'unity', 'source'
  ]).describe('The gate name to retrieve guardian info for'),
})

const SearchGuardiansSchema = z.object({
  element: z.enum(['earth', 'water', 'fire', 'wind', 'void', 'spirit']).optional(),
  query: z.string().optional().describe('Free text search across guardian descriptions'),
  limit: z.number().int().min(1).max(10).default(5),
})

const GUARDIAN_TOOLS = [
  {
    name: 'arcanea_lore_get_guardian',
    description: 'Get complete information about a Guardian including their Godbeast, gate frequency, element, and domain. Use when needing canonical guardian data.',
    inputSchema: {
      type: 'object' as const,
      properties: {
        gate: {
          type: 'string',
          enum: ['foundation','flow','fire','heart','voice','sight','crown','shift','unity','source'],
          description: 'The gate this guardian protects',
        },
      },
      required: ['gate'],
    },
  },
  {
    name: 'arcanea_lore_search_guardians',
    description: 'Search guardians by element or free text. Returns matching guardians with their domains and frequencies.',
    inputSchema: {
      type: 'object' as const,
      properties: {
        element: {
          type: 'string',
          enum: ['earth', 'water', 'fire', 'wind', 'void', 'spirit'],
        },
        query: { type: 'string' },
        limit: { type: 'number', minimum: 1, maximum: 10, default: 5 },
      },
    },
  },
]

export function registerGuardianTools(server: Server) {
  // List tools
  server.setRequestHandler(ListToolsRequestSchema, async () => ({
    tools: GUARDIAN_TOOLS,
  }))

  // Handle tool calls
  server.setRequestHandler(CallToolRequestSchema, async (request) => {
    const { name, arguments: args } = request.params

    switch (name) {
      case 'arcanea_lore_get_guardian': {
        const { gate } = GetGuardianSchema.parse(args)
        const { data, error } = await supabaseAdmin
          .from('guardians')
          .select('*, godbeast:godbeasts(*)')
          .eq('gate', gate)
          .single()

        if (error || !data) {
          return {
            content: [{
              type: 'text',
              text: `Guardian not found for gate: ${gate}. Valid gates: foundation, flow, fire, heart, voice, sight, crown, shift, unity, source.`,
            }],
            isError: true,
          }
        }

        return {
          content: [{
            type: 'text',
            text: JSON.stringify(data, null, 2),
          }],
        }
      }

      case 'arcanea_lore_search_guardians': {
        const { element, query, limit } = SearchGuardiansSchema.parse(args)
        let dbQuery = supabaseAdmin.from('guardians').select('id, name, gate, element, frequency_hz, domain')

        if (element) dbQuery = dbQuery.eq('element', element)
        if (query) dbQuery = dbQuery.textSearch('description', query)
        dbQuery = dbQuery.limit(limit)

        const { data, error } = await dbQuery
        if (error) {
          return {
            content: [{ type: 'text', text: `Search error: ${error.message}` }],
            isError: true,
          }
        }

        return {
          content: [{
            type: 'text',
            text: JSON.stringify(data, null, 2),
          }],
        }
      }

      default:
        return {
          content: [{ type: 'text', text: `Unknown tool: ${name}` }],
          isError: true,
        }
    }
  })
}

Phase 3: Resources (Read-Only Data)

// packages/arcanea-mcp/src/resources/canon-resource.ts
import { Server } from '@modelcontextprotocol/sdk/server/index.js'
import {
  ListResourcesRequestSchema,
  ReadResourceRequestSchema,
} from '@modelcontextprotocol/sdk/types.js'
import { readFile } from 'fs/promises'
import { join } from 'path'

const CANON_PATH = join(process.cwd(), '../../.arcanea/lore/CANON_LOCKED.md')

export function registerCanonResource(server: Server) {
  server.setRequestHandler(ListResourcesRequestSchema, async () => ({
    resources: [
      {
        uri: 'arcanea://canon/locked',
        name: 'Arcanea Canon (Locked)',
        description: 'The canonical source of truth for the Arcanea universe — gates, guardians, elements, frequencies.',
        mimeType: 'text/markdown',
      },
    ],
  }))

  server.setRequestHandler(ReadResourceRequestSchema, async (request) => {
    if (request.params.uri === 'arcanea://canon/locked') {
      const content = await readFile(CANON_PATH, 'utf-8')
      return {
        contents: [{
          uri: request.params.uri,
          mimeType: 'text/markdown',
          text: content,
        }],
      }
    }
    throw new Error(`Unknown resource: ${request.params.uri}`)
  })
}

Phase 4: Claude Code Integration

Register in .claude/mcp.json

{
  "mcpServers": {
    "arcanea-mcp": {
      "command": "bun",
      "args": ["run", "packages/arcanea-mcp/src/index.ts"],
      "env": {
        "SUPABASE_URL": "${NEXT_PUBLIC_SUPABASE_URL}",
        "SUPABASE_SERVICE_ROLE_KEY": "${SUPABASE_SERVICE_ROLE_KEY}"
      }
    }
  }
}

Design Principles

Tool descriptions must be actionable

// BAD — vague
description: 'Get guardian data'

// GOOD — tells the AI exactly when and how to use it
description: 'Get complete Guardian profile including Godbeast companion, gate frequency (Hz), element, domain, and lore description. Use when answering questions about a specific gate or guardian. Required param: gate name (foundation|flow|fire|heart|voice|sight|crown|shift|unity|source).'

Error messages guide toward solutions

// BAD
throw new Error('Not found')

// GOOD
return {
  content: [{
    type: 'text',
    text: `Guardian not found for gate "${gate}". Valid values: foundation, flow, fire, heart, voice, sight, crown, shift, unity, source. The gate "fire" maps to Guardian Draconia at 396 Hz.`,
  }],
  isError: true,
}

Input validation with Zod

// Always validate with Zod — catches bad AI inputs early
const schema = z.object({
  gate: z.enum(['foundation','flow','fire','heart','voice','sight','crown','shift','unity','source']),
  includeGodbeast: z.boolean().default(true),
})

// In handler:
try {
  const params = schema.parse(args)
} catch (e) {
  return { content: [{ type: 'text', text: `Invalid params: ${e.message}` }], isError: true }
}

Quick Checklist

Before shipping an Arcanea MCP tool:

• Tool name follows arcanea_{domain}_{verb}_{noun} convention
• Description tells AI exactly when to use and what params are required
• Input validated with Zod schemas
• Error messages include next steps and valid values
• Supabase uses admin client (service role) for MCP — not anon
• Registered in both src/index.ts and .claude/mcp.json
• TypeScript strict mode — no any
• Tool handles missing/empty results gracefully