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

Annotations only declare destructiveHint=true, so the description carries most of the burden and does so well: it confirms the mutation, discloses partial-update semantics (non-passed fields are preserved), gives the underlying endpoint PUT /contacts/{id}, and states the return value. It does not say what happens if the id doesn't exist or what errors look like.

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, zero filler, with the mutation warning and verb+resource leading. The escape-hatch hint is placed exactly where an agent would look for it.

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 partial-update tool with a nested `fields` object and no output schema, the description covers mutation semantics, the raw-field escape hatch, and the return value ('the updated contact'). Only failure/not-found behavior is unaddressed, a minor gap given the full schema coverage.

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 coverage is 100%, so every parameter including `fields` is already documented in the schema. The description's partial-update sentence adds real meaning about optional parameters, but its `fields` explanation largely restates the schema's own description. Baseline 3 is appropriate.

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 an existing contact') and front-loads the mutation nature with 'MUTATES Quaderno data'. It is trivially distinguishable from siblings like quaderno_create_contact and quaderno_get_contact without opening any schema.

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?

Clearly frames this as a partial update ('Only the fields you pass are changed') and points to `fields` as the escape hatch for untyped attributes, which tells the agent when this tool suffices. It stops short of naming alternatives or exclusions (e.g., use quaderno_create_contact when the contact doesn't exist yet).

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