messages_contacts

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

With no annotations, the description carries the burden and does disclose the sort order (most recent) and the returned fields (message count, last message date). However, it says nothing about auth requirements, pagination beyond the limit, or behavior on an empty mailbox, so it only partially fills the gap left by missing annotations.

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 tight sentences that front-load the core purpose and append the return-value detail. No filler or 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?

For a simple single-parameter read tool with no output schema, the description covers the operation, ordering, and returned fields adequately. Minor gaps around pagination behavior and prerequisites keep it just short of fully 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% and the single limit parameter is fully documented in the schema, so no description compensation is needed. The description adds no extra meaning about the parameter, making the baseline 3 correct.

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 (List) and scoped resource (contacts you've messaged, sorted by most recent), which clearly distinguishes it from contacts_search, contacts_lookup, and messages_recent. It does not explicitly name any sibling, but the messaging-scoped contact list 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?

There is no when-to-use or when-not-to-use guidance and no alternatives named. The purpose implies a use case (finding people you've corresponded with), but an agent gets no routing help versus contacts_search or person_search.

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