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

Annotations already declare readOnlyHint=true, so the safety profile is covered; the description adds real value beyond that by disclosing the returned payload shape (status, report ids, result) and mapping to the underlying REST call GET /checks/{check_id}. It stops short of mentioning error behavior for unknown ids, but for a read-only fetch that is minor.

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?

Two short sentences, zero filler, with the purpose front-loaded and the endpoint mapping appended as a compact reference. Every clause earns its place.

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?

No output schema exists, but the parenthetical list of returned fields (status + report ids + result) partially compensates by telling the agent what to expect back. Combined with the read-only annotation and the fully documented single parameter, this is nearly complete, missing only error/not-found behavior.

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 is a single parameter and schema description coverage is 100%, so the schema already documents check_id fully. The phrase 'by id' adds no syntax, format, or constraint detail beyond that, making the baseline 3 the correct score.

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 ('Retrieve a single check ... by id') and pins the scope to one record via 'single', which contrasts with the sibling onfido_list_checks. The parenthetical enumerates the returned fields, making the tool's job unambiguous, though it never names the sibling explicitly.

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?

Usage is only implied: 'by id' signals you must already hold a check id, and 'single' implies this is the lookup path versus onfido_list_checks. There is no explicit when-to-use, when-not-to-use, or prerequisite statement, so the agent must infer the routing from the name.

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