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Hosting tiers

Authoring a tool

A tool spec is one JSON object. Here's a complete real example — github_search_issues, written for the manifest tier.

{
  "spec_version": "1",
  "tool_name": "github_search_issues",
  "description": "Search GitHub issues by query",
  "hosting_tier": "manifest",
  "input_schema": {
    "type": "object",
    "properties": {
      "query": { "type": "string", "minLength": 1 }
    },
    "required": ["query"]
  },
  "requires_secrets": [
    {
      "name": "github_token",
      "description": "GitHub PAT, scope: repo",
      "env_hint": "GITHUB_TOKEN"
    }
  ],
  "http": {
    "method": "GET",
    "url": "https://api.github.com/search/issues?q={{input.query}}",
    "headers": {
      "authorization": "Bearer {{secret.github_token}}",
      "accept": "application/vnd.github+json"
    },
    "timeout_ms": 10000,
    "error_map": [
      { "status": "401", "code": -32010, "message": "GitHub token invalid" },
      { "status": "403", "code": -32020, "message": "Rate limited by GitHub" }
    ]
  },
  "response": {
    "map": "$.items[*].{number: number, title: title, url: html_url}",
    "body_type": "json"
  },
  "idempotent": true,
  "cache_ttl_seconds": 30
}

Template fields use Mustache-style {{input.x}} / {{secret.y}}. Nested templates are rejected. Every {{secret.x}} reference must be declared in requires_secrets — undeclared secrets fail validation at publish time.

Secrets model

When the consumer's MCP client calls a tool, secrets ride inside the JSON-RPC body, never as cookies or stored values:

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "github_search_issues",
    "arguments": {
      "query": "is:open label:bug",
      "_secrets": {
        "github_token": "ghp_xxx"
      }
    }
  },
  "id": 1
}

• •_secrets is stripped from arguments before the interpreter sees them. The gateway logs are redacted via pino's structured redaction; secrets never hit disk.
• •Tool args matching common token shapes (ghp_, sk_live_, etc.) are rejected if they appear outside _secrets — defense against publisher misuse.
• •Templates can reference {{secret.x}} only in http.url, http.headers, and http.body — never in response.map. Secrets are write-only into the upstream call.

Versioning

Three URL shapes, three guarantees:

Deprecated versions keep serving (consumers see a Deprecation: true response header). Archived versions return a structured error with data.upgrade_to so clients can prompt the user to migrate.

Security guarantees