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

Annotations already declare read-only and non-destructive behavior. The description adds valuable context about results ('Returns evidence') and the unusual 'optional confirmation-required official browser handoffs', which goes beyond the annotations and clarifies the tool's side-effect-free nature.

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 two sentences: the first front-loads the primary action and scope, the second adds a key boundary. There is no redundancy or filler, making it highly efficient.

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 structured output schema and annotations, the description adequately covers behavioral scope (search, evidence, optional handoffs, no booking) and search criteria. It omits details like pagination or limit behavior, but these are largely inferable from the schema, making it complete enough for agent selection.

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 what the query parameter can match (name, locality, address, etc.) and 'UK or US' maps to region. However, the 'service' and 'limit' parameters are not addressed, though their schema enums and defaults make them fairly self-explanatory.

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 ('Search') and a clear resource ('source-backed UK or US test-centre directory'), while enumerating searchable fields (name, locality, address, postcode/ZIP, alias, identifier). It distinguishes itself from siblings by focusing solely on test-centre lookup and explicitly notes it never books or changes a test.

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 context for when to use the tool: searching for test centres in the UK or US. It also states a clear exclusion ('Never books or changes a test') but does not explicitly name alternatives or elaborate on when not to use it relative to sibling tools.

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