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

With no annotations, the description carries the full burden and does so well: it discloses idempotency ('calling again with the same seq changes nothing'), monotonic cursor behavior ('never moves back or past the last stored message'), the read-receipt semantics the peer observes, and a side effect ('slides the channel's expiry'). This is exactly the behavioral context missing from structured fields.

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?

Every sentence earns its place and is dense with behavioral facts, with no filler. The lead sentence front-loads the client instruction rather than the tool's core effect, which slightly buries the most important framing.

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?

With no annotations and no output schema, the description still covers the invocation trigger, idempotency, cursor invariants, side effects, and the peer-visible consequence. Nothing an agent needs to call this correctly is missing.

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 100% so the two parameters are already documented, establishing a baseline of 3. The description adds genuine semantics for seq by explaining what 'processed' means behaviorally (monotonic, idempotent, tied to the read receipt), though it adds little for key beyond 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?

The description never states the verb 'acknowledge' directly, but it clearly conveys the purpose: advancing the read cursor so the peer sees messages as read. It distinguishes itself from channel_fetch by tying invocation to a prior peek fetch. An agent can identify what it does, though the framing is indirect rather than a crisp verb+resource statement.

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?

It explicitly says to use the local client rather than calling by hand, and pins the trigger condition: 'After a fetch with peek=true, the client calls this with the highest sequence number it processed.' Both the when-to-call and the preferred alternative are stated outright.

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