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

The readOnlyHint annotation already signals this is a read-only operation. The description adds that thread read-state is user-scoped and provides the endpoint, but it does not disclose return shape, pagination, authentication needs, or other behavioral details beyond what annotations already convey.

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 sentences with zero filler: definition, server-side usage note, and endpoint. The most important information is front-loaded.

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 query tool with all parameters documented in the schema, this is nearly complete. It includes the endpoint, the key user-scoping caveat, and a terse definition. It could be slightly stronger with explicit sibling routing or a note about return values, but nothing essential is missing.

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 baseline is 3. The description's note about user_id scoping read-state repeats what the schema already says ('scope thread participation/read-state to'), adding only the 'server-side calls should pass' nuance. No substantial new parameter meaning is provided.

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 states a specific action and resource: 'List threads' and clarifies that threads are 'messages with replies'. This makes the tool's purpose clear and distinguishes it from message/channel/user queries, though it does not explicitly name or contrast a sibling tool.

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?

It provides clear contextual guidance: server-side calls should include user_id to scope thread read-state to that user, and it gives the endpoint POST /api/v2/chat/threads. It does not explicitly discuss alternatives or when not to use this tool, but the context is clear enough for selection.

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