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

Annotations already declare the full safety profile (readOnly, idempotent, non-destructive, openWorld), so the description's job is to add context, which it does by disclosing that results aggregate across matches and rooms and that a cursor is returned. It omits any mention of pagination mechanics or rate limits, so it adds only modest value beyond annotations.

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?

A single front-loaded sentence with no filler, stating scope and return mechanism immediately. The only blemish is the ambiguous 'next_since cursor' phrasing, which does not match any parameter name.

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?

With no output schema and three optional parameters, the description is minimally adequate: it explains the scope and hints at the cursor loop, but it never states the pagination contract (feed the returned cursor back into `since`), nor the shape or ordering of returned messages. A short note on the polling loop would close the gap.

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 limit, since, and api_key are already documented; baseline is 3. The description contributes the notion that a cursor drives repeated calls, which enriches the `since` parameter, but it introduces a naming mismatch ('next_since') versus the schema's `since` that could confuse rather than clarify.

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 names a specific resource (new messages addressed to you) and scope (across matches and rooms), which implicitly distinguishes it from list_match_messages and fetch, which target a single match. It stops short of explicitly naming those siblings, so it does not reach 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?

There is no when-to-use or when-not guidance, and no alternatives are named despite a crowded sibling set (list_match_messages, fetch, search, get_handoff). The agent must infer that polling is the intended usage from the name alone.

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