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

The description goes beyond the single destructiveHint annotation by disclosing that the change is reversible and that no verification is triggered — exactly the kind of operational context annotations don't convey. The tension between "reversible" and destructiveHint=true is a nuance (fields are still overwritten), not a contradiction, but it leaves the overwrite behavior unstated.

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 behavioral caveat front-loaded before the endpoint reference; nothing is padded and the key differentiators (reversible, no verification) come first.

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 an 8-parameter mutation tool with nested objects and no output schema, the description covers purpose and safety posture but omits partial-update semantics and permission/auth expectations. Given the fully self-documenting schema, it is adequate but noticeably thin on the mutation side.

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 eight parameters (including the nested address and id_numbers pass-through objects) are already documented in the schema, making 3 the correct baseline. The description adds no format, constraint, or partial-update detail beyond what the schema provides.

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 ("Updates an applicant's details") plus the exact API endpoint, which unambiguously separates it from the get/list/create applicant siblings. It stops short of clarifying partial-vs-full replacement semantics, which would be the remaining distinguishing detail for an update tool.

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?

There is no explicit when-to-use or when-not guidance: nothing tells the agent to prefer this over onfido_create_applicant for new applicants, or how it relates to verification/check tools. Usage is only weakly implied by the word "Updates" and the applicant_id parameter.

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