PostalDataPI MCP Server

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It describes what the tool returns (metadata including coordinates, region, fields) and implies it's a read-only lookup operation. However, it lacks details on error handling, rate limits, authentication needs, or data freshness. The description adds basic behavioral context but misses deeper operational traits.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured and concise. It starts with the core purpose, lists key returns, provides usage guidelines, and details parameters and returns in labeled sections. Every sentence adds value without redundancy, making it easy to scan and understand quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's moderate complexity (2 parameters, no annotations, but has output schema), the description is fairly complete. It explains purpose, usage, parameters, and returns. The output schema exists, so the description doesn't need to detail return values extensively. It could improve by addressing potential errors or sibling differentiation, but it covers the essentials for agent use.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate. It explains both parameters: 'postal_code: The postal code to look up' and 'country: ISO 3166-1 alpha-2 country code. Defaults to "US".' This adds meaning beyond the bare schema, clarifying the country code format and default value. It doesn't detail validation rules or examples, but covers the essentials.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Get full metadata for a postal code including coordinates.' It specifies the verb 'Get' and resource 'postal code metadata' with key components like coordinates, county/municipality, and country-specific fields. However, it doesn't explicitly distinguish this from sibling tools like 'lookup_postal_code' or 'validate_postal_code', which likely have overlapping functionality.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear usage guidance: 'Use this when someone needs geographic coordinates, timezone, or detailed location data for a postal code.' This gives context for when to select this tool. It doesn't explicitly state when not to use it or name alternatives among the siblings, but the guidance is sufficient for typical agent decision-making.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.