Who needs a reply

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the key semantic rule for inclusion (other party sent last message), which is genuinely useful behavior beyond the annotations. It says nothing about ordering, result caps, or what a 'waiting' conversation excludes (e.g., archived, opted-out contacts).

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?

One sentence, zero filler, and the defining criterion is front-loaded ahead of the consequence ('so they're waiting on you'). Nothing could be removed without losing the filter definition.

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 single-parameter read tool with annotations covering safety and a fully documented schema, the description supplies the one thing structured fields cannot: the inclusion rule for 'unanswered'. It stops short of describing return shape or ordering, but no output schema exists and the tool is simple enough that this is a minor 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 description coverage is 100%, and the single parameter since_hours is documented in the schema with default 48, min 1, max 720. The description does not mention the lookback window at all, so it adds no meaning beyond the schema; baseline 3 applies.

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 defines a specific semantic filter: 'Conversations where the other person sent the last message, so they're waiting on you.' That is clear enough to distinguish it from generic listing (list_conversations) and single-item retrieval (get_conversation) siblings. It lacks an explicit verb like 'find' or 'list', which keeps it from 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 purpose implies when to use it (surfacing threads needing a reply), but there is no explicit when-to-use/when-not guidance, no mention of alternatives such as list_conversations, and no note on what happens with group threads or threads you started. Usage is inferred rather than stated.

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