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

The annotations already declare destructiveHint=true, idempotentHint=true, readOnlyHint=false, and openWorldHint=true, so the safety profile is covered. The description adds real value with 'Only the fields you pass are sent,' clarifying partial-update semantics, but the leading 'WRITE:' label largely restates readOnlyHint=false and nothing is said about permissions or what happens to fields omitted from the request.

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 short sentences with zero filler; the write semantics and scope lead, followed by the partial-update rule and the endpoint. Every sentence carries information the agent can act on.

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?

With 7 parameters, a nested object, and rich annotations, the description supplies the two things the schema cannot: write semantics and partial-update behavior. The only gap is that no output schema exists and the description says nothing about what the call returns or how failures surface, which is a minor omission for a PATCH tool.

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%; every parameter including the nested custom_fields slot mapping is documented in the schema itself. The description adds no per-parameter meaning beyond that, so the baseline 3 applies.

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 ('change fields of one contact in one list') plus the exact endpoint, so it is distinguishable from benchmark_add_contact by the change-vs-create verb. It stops short of explicitly naming or contrasting a sibling, which keeps it at 4 rather than 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?

Implicit use case (modify an existing contact) is inferable, but there is no explicit when-to-use guidance, no statement of when to prefer it over benchmark_add_contact or benchmark_unsubscribe_contact, and no prerequisites. Nothing routes the agent among alternatives.

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