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

With no annotations, the description carries the full load, and it does add genuinely useful behavior: partial merge semantics and a provenance rule stating that writes are attributed to a person and protected from a later 'Iris' read overwriting them. It still omits error behavior for an unknown contact_id, permission requirements, and any validation of field values, so coverage is partial.

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 tightly written sentences with no filler, and the write/merge semantics are front-loaded ahead of the provenance caveat. Slightly dense phrasing ('a later reading by Iris') but every clause carries information.

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?

Nine parameters are all documented in the schema, so the description's job is to cover behavior, which it does via the merge rule and the overwrite-protection note. What remains unaddressed is failure behavior and the shape of the response, which matters somewhat since there is no output schema.

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% with all nine fields individually documented, so the schema does the heavy lifting and baseline 3 applies. The description adds only the collective rule that unspecified fields are preserved, with no per-field detail beyond the schema.

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?

"Writes the fiche fields you pass, and leaves the others as they are" states a specific verb and a partial-update scope, which an agent can distinguish from a full replace. The resource is only implicit ('fiche', clarified by the title), and no sibling such as create_contact or get_contact is named, so it stops short of full differentiation.

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 indication of when to reach for this tool versus create_contact, get_contact or list_contacts. No prerequisites, no exclusions, and no scenario is described; the agent must infer all routing from the tool name alone.

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