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

Annotations already declare readOnlyHint=true, destructiveHint=false and idempotentHint=true, so 'this tool changes nothing' adds nothing. Worse, the description then documents update and bulk_update (including 'apply per-contact updates to up to 1,000 contacts asynchronously') as actions of this tool, which contradicts the read-only annotation and the schema enum. The only genuine added context is the async/1,000-contact note, which does not belong to this tool.

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?

The read-only constraint and action routing are front-loaded, which is good, but the second paragraph is a dense run-on enumerating every action and parameter, much of which duplicates the schema. It also repeats the destructive/read-only framing twice ('this tool changes nothing' and 'is refused here') while simultaneously documenting write actions.

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 read-only, 2-parameter wrapper over five actions with 100% schema coverage and no output schema, the definition covers every action's purpose, required params, prerequisites, and pagination knobs. The remaining gap is a self-inflicted one — the phantom update/bulk_update content — rather than missing information.

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% and already documents most fields, but the description adds per-action parameter mapping, marks which params are required per action, and flags the ordering default difference for list_messages (desc on received_at vs asc elsewhere). It stops short of explaining filter object composition beyond pointing at get_contact_filter_types.

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 first sentence states a specific verb and resource ('Read contacts') and the second enumerates the concrete actions (list, search, filter, get, list_messages) with their parameters, so an agent can tell it apart from contacts_manage. The clarity is undercut by the second paragraph, which reintroduces 'update' and 'bulk_update' as if they were actions of this tool even though the same description says writes are refused here.

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?

Strong routing guidance: writes are explicitly delegated to contacts_manage, filter requires calling get_contact_filter_types first, list_messages is preferred over last_messages to read beyond the latest 10, and 'provide exactly one' of id/username/email is stated. The guidance is weakened by the contradictory listing of update/bulk_update as available actions, which gives an agent two incompatible usage models.

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