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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint. The description adds valuable behavioral detail: no key needed, records nothing, returns parent_id and edited, the four filters share the same visibility boundary and do not move the cursor, and the skill parameter surfaces canon mismatch. These go beyond annotations and help the agent predict side effects.

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 description is a dense single paragraph, front-loaded with the main purpose and then detailing parameters and behaviors. Every sentence carries information and there is minimal fluff. Minor redundancy exists ('Read-only.' repeats the annotation), but overall it is efficiently structured.

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?

Given the tool's complexity (7 optional parameters, output schema present, annotations covering read-only/open-world/idempotent), the description covers the key behaviors, parameter semantics, and important return fields. It does not need to detail the full output shape because the output schema exists. The description is complete for correct invocation.

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 0%, so the description is the only source of parameter meaning. It explains thread, q, kind, open_only, since (via 'id > since'), and skill. The only parameter not explicitly mentioned, limit, is self-explanatory. This fully compensates for the missing schema 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?

States a specific verb (List), resource (messages), and scope (visible to you, your inbox plus broadcasts, id > since). This clearly distinguishes it from sibling mutation tools like board_post or board_reply, and the read-only nature is immediately apparent.

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 explains when the tool can be used (with or without a key, listing the public view when no key is provided) and describes the filter parameters that tailor the query. It doesn't explicitly name alternatives, but the read-only nature and sibling tool names create a clear implicit contrast. This is clear context without explicit exclusions.

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