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

Annotations already convey read-only, idempotent, non-destructive behavior. The description adds behavioral value by naming the external FCC Census Block API, stating that no API key is required, and enumerating the returned fields. It does not mention rate limits or invalid-coordinate behavior, but the annotation coverage lowers that burden.

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 four sentences and each adds information: action and scope, return fields, use cases, and authentication status. It is somewhat longer than strictly necessary but remains well-structured and front-loaded with the core purpose.

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?

For a read-only lookup tool with full schema coverage, output schema, and safety annotations, the description covers the essential facts: what it returns, why to use it, and the fact that no API key is needed. Missing details like behavior for non-US or invalid coordinates are minor and partially implied by 'US latitude/longitude coordinate.'

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 100% and all three parameters already have clear descriptions and an enum for census_year. The description adds little parameter-specific meaning beyond framing the input as US latitude/longitude coordinates, so the baseline score of 3 applies.

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 uses a specific verb ('Look up') and resource ('US Census Block FIPS code, county FIPS, and state') and ties it to the FCC Census Block API. It clearly distinguishes this tool from sibling reverse geocoders and address tools by focusing on Census Block FIPS output rather than street addresses.

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 gives clear usage context: determining regulatory jurisdiction, broadband program, or census reporting area for a US coordinate. It does not explicitly name alternative tools or state when not to use it, but the domain-specific use cases make the intended context clear.

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