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

Beyond the annotations, the description discloses two non-obvious traits: PATCH-style partial semantics (unpassed fields are preserved) and that no notification is sent to the contact. It does not address the destructiveHint=true implication — that overwritten values are replaced and not recoverable — nor any permission requirements.

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 tight clauses, front-loaded with the operation type and scope, with zero filler. Every statement carries information an agent needs.

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 15-parameter mutation with no output schema, the description covers the core semantics (partial update, single record, no notification) but says nothing about failure behavior, whether contact_id must exist, or what the response contains. Adequate as a minimum but with clear gaps.

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 only 13% across 15 parameters; only contact_id and language are documented in the schema, leaving the other 13 fields' semantics to field names alone. The description adds only the partial-update rule and no per-parameter guidance, so it does not compensate for the coverage gap.

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 existing contact'), scoped to a single record, which cleanly separates it from bookingmood_create_contact and the list/get siblings. The 'WRITE:' prefix and the PATCH endpoint make the operation type unmistakable.

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?

The clause 'only the fields you pass are changed; others stay' tells the agent this is a partial update and implies it should be used for editing existing contacts rather than creating them. It lacks an explicit exclusion (e.g. don't use for creating, or a pointer to create_contact for new records), so it falls short of 5.

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