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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds genuinely non-derivable context: the underlying Census Gazetteer/relationship-file/ACS 2020-2024 data, straight-line rather than driving distance, and the cap of 20 candidate areas. Only the 250-default listing behavior is left to the schema.

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?

Three sentences, front-loaded with the purpose, then inputs, then outputs and caveats. Dense but every clause carries information (data sources, distance semantics, candidate-area cap); no filler or repetition of the title.

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?

There is no output schema, yet the description fully specifies the return contents — ZCTA-level fields, places, counties with in-area population, totals, and GBP candidates — plus the straight-line distance caveat. For a 4-param read-only analytic tool, an agent has everything needed to call and interpret it.

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%, so every parameter (base, zips, max_zips, radius_miles) is already documented with formats, ranges and defaults. The description restates the ZIP/'City, ST' format and the base-vs-zips choice but adds no syntax or edge-case detail beyond the schema, which is the correct baseline for full coverage.

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 opens with a specific verb+resource ('Work out what a local service business covers') and then enumerates exactly what is computed: ZCTAs with distance/population/housing, places, counties, totals, and up to 20 GBP candidate areas. An agent can tell precisely what this tool produces, and the sibling tools (trades, demand, review timing) share no overlap.

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?

It clearly states the two accepted input modes ('Give a base ... and a radius in miles, or a list of ZIPs'), which tells the agent how to invoke it, and the schema reinforces that base pairs with radius_miles. It does not state when to prefer one mode or when not to use this tool, but the sibling set offers no competing alternative, so the gap is minor.

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