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

Annotations already flag this as destructive and non-idempotent, so the description does not need to restate that. It adds genuinely new behavioral detail by explaining patch semantics — only supplied inputs change, while 'tags' and 'fields' are wholesale replacements — which is exactly the asymmetry an agent would otherwise get wrong.

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 short sentences, both doing work; the crucial collection-replacement warning is included without padding.

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 12-parameter mutation with no output schema, the description covers the highest-risk ambiguity (list/map replacement) but omits clearing semantics via null, whether unset optional fields are left untouched, and any indication of the response. Adequate 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 25% across 12 parameters, so the description must carry weight. It clarifies the replace-versus-patch semantics for 'tags' and 'fields' but says nothing about the eight nullable string parameters, including how null clears a value, nor about phone_number formats or field value limits.

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 ('Update a contact'), which an agent can act on. It does not differentiate itself from close siblings like upsert_contact or bulk_update_contacts, and does not say what it cannot do, 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?

There is no guidance on when to use this instead of upsert_contact or bulk_update_contacts, and no mention of prerequisites such as needing an existing contact id. The agent must infer usage from the name alone.

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