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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds value beyond them by disclosing the exact result set size (11 regions), the fields returned, the geographic exclusion, and the 1-credit cost — a real operational constraint for budgeting calls.

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 tight sentences: what it returns, what to use it for, and what it excludes, with the cost note at the end. Front-loaded with the resource and scope, no filler or repetition of the name.

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 zero-parameter lookup with no output schema, the description covers the result cardinality, the fields returned, the intended downstream use and the geographic gap. It lacks only a note on output ordering or format, which is minor given no output schema exists.

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?

There are zero parameters, so the baseline is 4. The description usefully explains that the output carries region_id, ONS codes and country, which is meaning about the payload beyond the empty schema and is exactly what an agent needs to chain into the traffic tool.

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?

States a specific verb and resource (lists the 11 GB regions DfT uses for traffic statistics) and enumerates coverage exactly — nine English regions, Scotland, Wales — plus the fields returned (DfT region ids, ONS codes, country). It is unmistakably distinct from region_traffic_by_vehicle_type.

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?

Explicitly names when to use it: to obtain the region_id needed for region_traffic_by_vehicle_type. It also states a boundary condition (Northern Ireland is not covered by DfT road traffic statistics), so an agent knows when this tool does not apply.

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