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

The description adds behavioral context by explaining the state change ('restoring their unread status') and the bulk single-call behavior. This complements the annotations (idempotentHint, destructiveHint) without contradicting them, though it does not cover side effects or authorization requirements.

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 no filler: the first states the action and effect, the second gives the key usage constraint. It is front-loaded and every sentence earns its place.

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 simple two-parameter mutation with fully documented schema and annotations, the description covers the operation and the critical batching behavior. It does not describe return values, but no output schema exists and the safety profile is already carried by annotations. A brief mention of the opposite action (mark_read) would make it complete.

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 uids parameter description already explains batching limits, sourcing, and single-message usage. The tool description's 'Pass the whole set in one call' lightly reinforces the schema but adds no new parameter meaning, so the baseline 3 is appropriate.

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 the action ('Mark messages as unread') and the outcome ('restoring their unread status'), giving a specific verb and resource. It differentiates from the sibling mark_read mainly through the tool name rather than explicit textual contrast, so it falls just short of 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 only usage guidance is the batching instruction 'Pass the whole set in one call,' which is a how-to rather than a when-to-use directive. It does not mention mark_read or other alternatives, so when to choose this tool over siblings is implied by the name rather than explicit.

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