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

Annotations only supply destructiveHint=true, so the description carries most of the behavioral load and does so well: it discloses merge semantics ('only supplied fields are changed') and that `extra` is merged verbatim, which are the traits an agent most needs to avoid clobbering data. It does not state permission requirements or what the call returns, so it falls short of a 5.

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 compact sentences, front-loaded with the core action and the id requirement, then the mutation semantics, then the raw endpoint for API-level mapping. No filler or repetition.

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 mutation tool with full schema coverage and no output schema, the description covers the action, the required id, the field set, and partial-update behavior. The one meaningful omission is what happens on return (updated contact object vs. empty body), which an agent editing a contact might need to confirm.

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%, so every parameter is already documented in the schema and the baseline is 3. The description enumerates the same field names (given_name, family_name, email_addresses, phone_numbers, company_id, extra) without adding syntax, format, or slot conventions beyond what the schema already provides.

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?

The description gives a specific verb and resource ('UPDATE an existing contact by id') and the word 'existing' plus the id requirement cleanly separates it from keap_create_contact, keap_get_contact, and keap_list_contacts. The added Keap endpoint mapping (PATCH /contacts/{contact_id}) reinforces exactly which operation this is.

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?

Usage is implied rather than stated: the agent can infer this is for modifying a contact that already exists, and the 'only supplied fields are changed' clause signals a partial-update pattern. However, there is no explicit when-to-use rule, no prerequisite/permission guidance, and no direct pointer to siblings like create_contact or get_contact.

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