{
  "id": "mcp-at-scale",
  "title": "MCP Tool Discovery Workbench",
  "level": 4,
  "levelName": "Systems",
  "tagline": "A scoped MCP inventory server that discovers schemas inside a measured context budget.",
  "summary": "A scoped MCP inventory server that discovers schemas inside a measured context budget. Run python3 cli.py /absolute/inventory.json --serve as a stdio server. tools/call catalog_search takes query, max_chars and k; the response returns selected public schemas and their character count.",
  "hours": 10,
  "languages": ["Python", "TypeScript"],
  "status": "ready",
  "source": "core",
  "author": {
    "name": "AI Engineering from Scratch",
    "github": "rohitg00"
  },
  "youWillBuild": "A scoped MCP inventory server that discovers schemas inside a measured context budget.",
  "usefulFor": [
    "Run python3 cli.py /absolute/inventory.json --serve as a stdio server. tools/call catalog_search takes query, max_chars and k; the response returns selected public schemas and their character count."
  ],
  "skills": [
    "Build a catalog of 250 read-only tools",
    "Select tools under an explicit context budget",
    "Implement initialized JSON-RPC over stdio",
    "Audit catalog coverage through protocol pages"
  ],
  "prerequisites": [
    "Python 3.10+, Node 22.18+, dictionaries, JSON-RPC request ids, stdin/stdout and child processes."
  ],
  "figures": true,
  "overviewFigure": "pj-mcp-at-scale-1",
  "languageWhy": {
    "Python": "Stdlib data structures, explicit algorithms and deterministic local tests.",
    "TypeScript": "Typed wire messages and real subprocess integration."
  },
  "demo": {
    "cwd": "solution",
    "command": [
      "python3",
      "cli.py",
      "samples/inventory.json",
      "--query",
      "pods count",
      "--max-chars",
      "500"
    ]
  },
  "stages": [
    {
      "id": "01-registry",
      "title": "Build a catalog of 250 read-only tools",
      "summary": "The generated catalog contains exactly 250 unique tools.",
      "language": "python",
      "languageWhy": "Python standard-library collections, bytes and file operations expose this stage directly.",
      "hours": 2,
      "difficulty": "starter",
      "figure": "pj-mcp-at-scale-1",
      "concepts": ["build", "a", "catalog", "of"]
    },
    {
      "id": "02-discovery",
      "title": "Select tools under an explicit context budget",
      "summary": "The query pods count selects pods_count first and never exceeds the serialized budget.",
      "language": "python",
      "languageWhy": "Python standard-library collections, bytes and file operations expose this stage directly.",
      "hours": 2,
      "difficulty": "core",
      "figure": "pj-mcp-at-scale-2",
      "concepts": ["select", "tools", "under", "an"]
    },
    {
      "id": "03-protocol",
      "title": "Implement initialized JSON-RPC over stdio",
      "summary": "A call before initialization returns -32002; an initialized tools/list returns 32 tools and a cursor.",
      "language": "python",
      "languageWhy": "Python standard-library collections, bytes and file operations expose this stage directly.",
      "hours": 2,
      "difficulty": "core",
      "figure": "pj-mcp-at-scale-3",
      "concepts": ["implement", "initialized", "json-rpc", "over"]
    },
    {
      "id": "04-audit",
      "title": "Audit catalog coverage through protocol pages",
      "summary": "An exhaustive traversal returns 250 unique names across 8 pages.",
      "language": "python",
      "languageWhy": "Python standard-library collections, bytes and file operations expose this stage directly.",
      "hours": 2,
      "difficulty": "stretch",
      "figure": "pj-mcp-at-scale-4",
      "concepts": ["audit", "catalog", "coverage", "through"]
    },
    {
      "id": "05-typed-client",
      "title": "Exercise the real wire with a typed client",
      "summary": "Spawn the Python server and verify every serialized response from TypeScript.",
      "language": "typescript",
      "languageWhy": "Node streams and explicit TypeScript interfaces make the process boundary visible.",
      "hours": 2,
      "difficulty": "stretch",
      "figure": "pj-mcp-at-scale-5",
      "concepts": ["stdio", "correlation", "timeouts"],
      "runners": [
        {
          "language": "typescript"
        },
        {
          "language": "python"
        },
        {
          "language": "python",
          "optional": true,
          "requires": ["python:mcp"],
          "argv": [
            "{python}",
            "-m",
            "unittest",
            "discover",
            "-s",
            "{stage}/tests-framework",
            "-p",
            "test_standard_client.py"
          ]
        }
      ]
    }
  ],
  "demos": [
    {
      "gif": "media/run.gif",
      "poster": "media/run.png",
      "title": "Initialize and grade",
      "caption": "Recorded starter failure followed by all reference-solution stages passing. Reference passes do not earn learner certificates."
    },
    {
      "gif": "media/output.gif",
      "poster": "media/output.png",
      "title": "Inspect the output",
      "caption": "Actual output from the local deterministic demo command. See the README for fixture and live-adapter limits."
    }
  ]
}