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

readOnlyHint=true already tells the agent this is a safe non-mutating read, so the description's disclosure burden is light. It usefully adds the shape of what comes back (status, report ids, result), which matters because there is no output schema, but says nothing about auth, rate limits, or missing-id behavior.

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 tight sentences with the identifier and return contents front-loaded, plus the underlying endpoint reference. No filler whatsoever.

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 simple single-resource fetch with a fully documented id parameter, this covers purpose, input, and rough return shape, which compensates for the absent output schema. Only the lack of any usage routing (list vs get) leaves a small gap.

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 check id.' in the schema carries the semantics and the description adds no syntax, format, or sourcing detail beyond 'by id'. Baseline 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?

States a specific verb (Retrieve), resource (a single check), keyed by id, and even names the returned fields (status, report ids, result), which implicitly contrasts with the onfido_list_checks sibling. It never names that sibling explicitly, so it stops short of a 5.

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 implied rather than stated: 'single ... by id' suggests this is the lookup path when you already hold a check_id, versus the list sibling for discovery. There is no explicit when-to-use/when-not guidance, no prerequisite or error conditions (e.g. unknown id).

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