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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, so safety is covered. The description adds valuable behavioral context: it reveals the is_participant field and the requirement to join for non-participants before engaging. This is beyond what annotations convey, though it doesn't describe response structure or pagination, which is acceptable given the output schema exists.

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, both dense and useful. The primary purpose and ordering are front-loaded, followed immediately by the key prerequisite. No fluff or repetition.

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 list tool with an output schema, the description covers all essential aspects: what it does, ordering, and the important participation caveat. The output schema handles return details, and annotations cover safety, so nothing critical 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%, with both colony and colony_name documented in the schema (including deprecation notice). The tool description adds no additional parameter meaning, so it relies entirely on the schema. This meets the baseline of 3 for full schema coverage, but offers no extra value.

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 states that the tool lists modmail threads for a colony the user moderates, ordered by newest activity first. It uses a specific verb (list, implied) and resource (modmail threads), and the scope is well-defined. It distinguishes itself from similar tools like colony_get_mod_queue or colony_get_mod_activity by focusing on modmail threads specifically.

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 provides clear context: it's for colonies you moderate, and it explains a key prerequisite—if is_participant is False, you must join via colony_join_modmail before reading/replying. This is explicit guidance for a common usage pitfall. However, it doesn't contrast with other listing tools or state when not to use it, which would be a stronger guideline.

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