Look up the boundaries containing a coordinate

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

Annotations only provide readOnlyHint=true and openWorldHint=true. The description adds substantial behavioral context: municipal is the finest unit available, non-matching layers return null, the errors array is always present with skipped sets, and the billing behavior ('one billed lookup however many layers...'). These go far beyond the annotations and directly inform how the agent should interpret results and costs.

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 longer than average but every sentence carries information: purpose, use-for, do-not-use-for, caveats, error handling, and billing. It is front-loaded with the core function and uses clear paragraph breaks. A slight reduction would be possible, but there is no fluff or repetition, so it earns a high score.

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 tool with 7 parameters and no output schema, the description is highly complete: it covers usage scope, exclusions, caveats about municipal granularity, null results, the always-present errors array, and billing implications. It does not explicitly describe the JSON response shape beyond 'names plus ISO 3166 codes', which would be helpful, but given that the schema and examples are absent, it still provides enough context for an agent to call it correctly.

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 all 7 parameters are already documented individually. The description does not add per-parameter detail, but it integrates the parameters conceptually (layers, sets, grid codes) and clarifies that some parameters only affect output encoding. This is adequate but not a significant improvement over the schema, so the baseline of 3 is appropriate.

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 and resource — 'Reverse geocode a coordinate ... as names plus ISO 3166 codes, and match it against boundary sets' — and clearly differentiates itself from siblings list_boundary_sets, create_boundary_set, and add_boundary, which are about managing boundary sets rather than geocoding. No ambiguity about what the tool does.

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 explicitly lists when to use the tool ('Use for: which country, region or municipality a point is in...') and when not to use it ('Do NOT use for: street addresses or postcodes... routing, distances, or fetching boundary geometry'). The exclusions and the reason ('results stop at the municipality') make the decision boundary unambiguous.

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