list_messages

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

With no annotations, the description carries the burden of behavioral disclosure. It reveals important behavior beyond the schema: one row per thread, direction omission merging both directions, and the searchable fields (subject/from/to/body). This is strong for a read-only list operation, though it does not mention response shape or pagination behavior.

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, front-loaded with the core purpose and followed by high-value usage nuances. No filler or repetition of schema details; every clause earns its place.

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 list tool with six parameters and no output schema, the description covers the non-obvious semantic decisions (threading, direction handling, search scope) while the schema documents the rest. A brief note on the returned fields or pagination would make it fully complete, but the tool can be invoked correctly with the current description.

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%, so the baseline is 3, but the description adds real value beyond the schema. It clarifies that q searches subject/from/to/body and that direction controls whether Inbox and Sent are merged. These nuances are not recoverable from the parameter descriptions alone.

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 clearly identifies the operation: listing messages for a mailbox, with the useful clarification 'one row per thread.' It is clear enough to distinguish from list_drafts or get_message, but it does not explicitly name sibling alternatives, so it stops short of a 5.

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 gives practical guidance: pass direction to split Inbox/Sent and pass q for full-text search. It explains the consequence of omitting direction ('merges both'), which helps the agent decide on parameters. It does not explicitly discuss when to prefer a sibling tool, but the usage context is otherwise clear.

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