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

readOnlyHint=true already tells the agent this is a safe read. The description adds no behavioral context beyond restating that it is a GET /contacts call — nothing about pagination behavior, default result size, or how deleted/modified filters affect output. It does not contradict the annotations, but it contributes almost nothing.

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 clauses, purpose front-loaded with no filler. The 'Missive: GET /contacts' tail is marginal value (API mapping) but costs little.

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 7-parameter read-only list tool with full schema coverage and no output schema, the essentials are covered by structured fields. However, nothing explains the return shape or pagination semantics, and usage context versus sibling list/get tools is absent, so it is only minimally complete.

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 limit, order, offset, search, modified_since, include_deleted, and contact_book are all documented in the schema with defaults and formats. The description adds no param-level meaning beyond that, so the baseline 3 applies.

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 ('List contacts in a contact book'), which is enough to separate it from missive_get_contact and missive_list_contact_books. It does not explicitly name a sibling, but the scope (list, within a book) is unambiguous.

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?

No guidance on when to choose this over missive_get_contact (single contact), missive_list_contact_books, or missive_list_contact_groups. The only context offered is the endpoint mapping and the implied scoping to a contact book, which is already implied by the required parameter.

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