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

Annotations already cover the safety profile (idempotent, non-destructive, closed-world). The description adds real semantic context beyond them: acknowledging means only 'retrieved', not 'understood', 'acted on', or 'answered' – important for interpreting the write. It omits failure behavior for stale or unknown receipts, so not a 5.

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?

Three tight sentences that front-load the action and follow with the precondition and semantic caveat. Dense parenthetical '(inbox:ack)' is the only minor clutter; nothing is padded.

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 mutating, non-read-only tool with no output schema, the description covers intent and timing but says nothing about what happens on partial or invalid acknowledgements, retry/idempotency behavior (only hinted via annotations), or confirmation of success. Adequate but with clear gaps.

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 0%, so the description must compensate. 'Exact returned sequence/receipt pairs' usefully conveys that receipts must be the verbatim values from the retrieval rather than fabricated, but client_id is never mentioned and the 1–100 batch bounds are left entirely to the schema.

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?

States a specific verb ('explicitly mark ... as retrieved') and a precise resource ('exact returned sequence/receipt pairs', inbox:ack), which is enough to separate it from check_inbox's retrieval role. It does not name any sibling explicitly, so it lands just short of fully differentiated.

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?

'Use only after successfully retrieving the batch' is an explicit precondition that gates invocation on a prior retrieval. It gives no explicit alternative or exclusion (e.g., what to do instead if retrieval failed), so it stops short of 5.

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