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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real protocol semantics beyond that: the at-least-once delivery model and the auto-ack behavior of non-peek reads. It does not cover edge behavior such as acking a stale/unknown cursor or what happens on replay, which keeps it out of the top band.

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, each earning its place: the action, the positive protocol, then the exclusion. The core operation is front-loaded before the usage detail.

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 1-required-param cursor acknowledgement with no output schema, the description plus annotations plus full schema coverage give an agent enough to call it correctly. The only gap is error/edge behavior (invalid cursor, re-ack after failure), which is minor given idempotentHint=true.

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 cursor, watch_id and client_token are all already documented in the schema, including the auth fallback for client_token. The description only echoes cursor provenance ('the cursor get_changes returned') without adding format or constraint detail, so the 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?

States a specific verb and resource ('Mark changes up to a cursor as processed') and explicitly positions itself against the sibling get_changes, naming the non-peek path. An agent can distinguish ack_changes from get_changes/delete_watch without opening either schema.

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?

Gives the exact usage protocol: pair with get_changes(peek=true), act, then ack the returned cursor. It also states the negative case — ack is unnecessary when get_changes is called without peek, since that acknowledges automatically — so there is no ambiguity about when to invoke this tool.

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