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

Annotations already declare idempotentHint=true and destructiveHint=false, and the description usefully reinforces and extends this by explaining the monotonic semantics ('acknowledging a lower seq changes nothing') and the capacity-freeing effect. It does not cover permissions or what happens to unacknowledged messages, so it adds solid but not exhaustive context.

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 short sentences, no padding, with the core action and its boundary front-loaded before the monotonic caveat and the effect.

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?

An output schema exists so return values need not be explained, and the description covers the mutation's effect and idempotency. The only real gap is the undocumented agent_id parameter, which is minor for a two-parameter tool.

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 50%: seq is documented in the schema (including the monotonic note) and the description restates 'up to seq', while agent_id carries no prose in either place. The description adds marginal meaning beyond the schema, fitting the baseline for partial coverage.

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 (mark as handled) and resource (messages in an agent inbox) with the seq boundary spelled out. It does not name a sibling such as city_read_inbox or city_ack_mentions to distinguish itself, so it stops 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 purpose ('Frees inbox capacity') implies when the tool is useful, but there is no explicit when-to-use/when-not guidance and no routing to the obvious alternatives (city_read_inbox for reading, city_ack_mentions for mentions). Usage is only inferable.

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