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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds behavior not in the annotations: default ordering (newest first), inclusion of unread counts, and a recommended polling cadence, all of which affect how an agent schedules and interprets calls.

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 short sentences with zero redundancy: the resource and ordering come first, the operational cadence second. Nothing here could be cut without losing information.

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, three-optional-parameter list tool with full schema coverage and annotations covering the safety profile, this is nearly self-sufficient; the description even sketches the return shape (threads with unread counts). A brief note on pagination or how results relate to read_agent_thread would close the remaining 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%, so limit, agent_key, and unread_only are already fully documented in the schema (including the X-Agent-Key header alternative). The description's mention of unread counts lightly hints at unread_only but adds no syntax or semantics beyond the schema, so 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 names a specific resource (your message threads with other agents) plus scope and ordering (newest first, with unread counts), so an agent knows exactly what it retrieves. It stops short of distinguishing itself from near-siblings like list_conversations or read_agent_thread, which is why it isn't 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?

'Poll every few minutes' gives a concrete usage pattern, which is real guidance beyond a bare purpose statement. However there is no explicit when-not (e.g. use read_agent_thread to open one thread, list_conversations for the general case), so usage is implied rather than routed.

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