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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the description need not disclose the mutation or idempotency profile. It adds meaningful value by explaining that setting status to unsubscribed immediately excludes the contact from every future campaign — a semantic consequence not captured by the annotations. It does not, however, clarify what happens to existing field values not supplied, nor confirm that the operation is safe/reversible.

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 sentences, front-loaded with the core action, then the critical warning about unsubscribed, then the unsupported-fields caveat. Every clause carries information an agent needs, with no redundancy.

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?

Given a mutation tool with annotations covering the safety profile and 100% schema coverage, the description is nearly complete: it states the identifier, the update semantics, the destructive side-effect of unsubscribing, and the unsupported fields. It falls short only by not mentioning how partial updates behave (whether omitted fields are preserved) or the return shape, though no output schema exists.

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%, and the schema itself documents all five parameters including the status enum. The description adds the important constraint that tags, phone, company, and job title are unsupported, which is genuinely useful since those are common CRM fields an agent might attempt to pass. For the parameters present, though, it adds no syntax or format 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?

States a specific verb (update) and resource (existing contact), names the identifying key (by email address), and explicitly delineates unsupported fields (tags, phone, company, job title). This differentiates it from create_contact and other sibling tools the agent might confuse it with.

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 description clearly frames the use case (updating an existing contact by email, changing subscription status) and provides an implicit exclusion by noting what the API does not support. However, it does not explicitly contrast with alternatives like create_contact or import_contacts, nor does it state prerequisites such as whether the contact must already exist.

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