Convert between YAML and JSON via @mukundakatta/yaml-mcp (npx)

Recipe: Convert YAML ↔ JSON via @mukundakatta/yaml-mcp (npx)

Surface: @mukundakatta/yaml-mcp v0.1.0 (npm) — bin name mcp-yaml Transport: stdio (JSON-RPC 2.0, newline-delimited) Auth: none required Tools: 2 — to_json, to_yaml

Server info

name: "yaml", version: "0.1.0"
capabilities: tools

Tool schemas

{
  "name": "to_json",
  "description": "Parse YAML and return the JSON-compatible value.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "text": { "type": "string", "description": "YAML source." },
      "all_documents": { "type": "boolean", "default": false, "description": "If true, parse a multi-document YAML stream and return an array of docs." }
    },
    "required": ["text"]
  }
}

{
  "name": "to_yaml",
  "description": "Serialize a JSON-compatible value to YAML.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "value": { "description": "JSON value to serialize. Any type." },
      "indent": { "type": "integer", "default": 2, "description": "Indent width." }
    },
    "required": ["value"]
  }
}

Setup & gotcha

Important: The npx -y @mukundakatta/yaml-mcp approach silently fails because of an import.meta.url guard in the entry point. You must either:

• Install globally: npm install -g @mukundakatta/yaml-mcp then run node $(npm root -g)/@mukundakatta/yaml-mcp/dist/server.js
• Or spawn the dist/server.js file directly after npx caches the package

Verified trace

Request: to_json — parse a YAML server config into JSON

{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"to_json","arguments":{"text":"name: my-api\nversion: 2.1.0\nserver:\n  port: 8080\n  host: 0.0.0.0\n  cors:\n    origins:\n      - https://app.example.com\n      - https://staging.example.com\n    methods: [GET, POST, PUT, DELETE]\ndatabase:\n  url: postgres://localhost:5432/mydb\n  pool_size: 10\n  ssl: true\nfeature_flags:\n  new_dashboard: true\n  beta_api: false"}}}

Response: (truncated for readability)

{"result":{"content":[{"type":"text","text":"{\"value\":{\"name\":\"my-api\",\"version\":\"2.1.0\",\"server\":{\"port\":8080,\"host\":\"0.0.0.0\",\"cors\":{\"origins\":[\"https://app.example.com\",\"https://staging.example.com\"],\"methods\":[\"GET\",\"POST\",\"PUT\",\"DELETE\"]}},\"database\":{\"url\":\"postgres://localhost:5432/mydb\",\"pool_size\":10,\"ssl\":true},\"feature_flags\":{\"new_dashboard\":true,\"beta_api\":false}}}"}]},"jsonrpc":"2.0","id":3}

Request: to_yaml — serialize a Kubernetes ConfigMap JSON to YAML

{"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":"to_yaml","arguments":{"value":{"apiVersion":"v1","kind":"ConfigMap","metadata":{"name":"app-config","namespace":"production","labels":{"app":"my-api","env":"prod"}},"data":{"DATABASE_URL":"postgres://db:5432/prod","REDIS_URL":"redis://cache:6379","LOG_LEVEL":"info","MAX_CONNECTIONS":"100"}}}}}

Response:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
  namespace: production
  labels:
    app: my-api
    env: prod
data:
  DATABASE_URL: postgres://db:5432/prod
  REDIS_URL: redis://cache:6379
  LOG_LEVEL: info
  MAX_CONNECTIONS: "100"

Notes

• Backed by the yaml npm package (YAML 1.2 compliant)
• to_json wraps parsed value in {"value": ...} — unwrap in your agent
• to_yaml accepts any JSON-serializable value, not just objects
• all_documents: true handles multi-doc YAML streams (separated by ---)
• indent param controls YAML output indentation (default 2 spaces)
• Numeric strings like "100" are preserved as strings in YAML output (correctly quoted)