search_messages

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

Annotations already declare readOnlyHint=true and idempotentHint=true, and the description adds substantial behavioral detail beyond that: it scans backwards, matches case-insensitive substrings, stops under three named conditions, and tells the agent to check oldest_message_reached and note before concluding absence. This is rich, actionable transparency.

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 with no wasted words. The main purpose is front-loaded, the usage guideline follows, and the operational caveat about scan depth is placed at the end where it is most useful as a caution.

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 6-parameter search tool with 100% schema coverage, rich annotations, and an output schema, the description is complete. It covers the algorithm, stop conditions, case-insensitivity, the read_messages alternative, and the critical caveat about interpreting scan limits.

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 the baseline is 3. The description adds value by explaining how the parameters interact: query matches message text, sender_name matches sender display names, both are case-insensitive substrings, and limit/max_messages_scanned act as stop conditions during the backward scan. This goes beyond the schema's individual field descriptions.

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 opens with a specific verb and resource: 'Search one conversation's message history for matching messages.' It clearly distinguishes the tool from read_messages by framing it as the targeted alternative to manual paging, so an agent can tell them apart immediately.

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 explicitly says when to use this tool — for finding specific messages like 'who mentioned pizza?' — and names the alternative read_messages for manual paging. This gives the agent a clear routing decision with a concrete condition.

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