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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds important non-obvious behavior beyond that: it defaults to a 7-day window and exposes a cursor mechanism via checkedAt for continuous, gap-free retrieval.

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, front-loaded with the core purpose and followed by the default and continuation pattern. Every sentence earns its place with no filler.

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?

Complete enough for a low-complexity read tool: annotations cover safety, the schema fully documents both parameters, and the description adds the polling cursor behavior. Missing sibling routing and any mention of the limit parameter are minor 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 100%, so the baseline is 3. The description adds meaningful semantics for since by explaining that a returned checkedAt should be fed back into it for gap-free diffs, though it does not add anything for the limit parameter.

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 clear resource and scope: what is new in the lists this person can access since a point in time. It distinguishes itself from a single-list update tool by saying 'lists this person has access to,' but it does not explicitly name or contrast sibling get_list_updates or my_library.

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?

Provides useful usage guidance for polling: defaults to the last 7 days and tells the agent to pass the returned checkedAt back as since for a gap-free diff. However, it does not say when to use this instead of alternatives like get_list_updates or search_library, so usage remains implied rather than explicit.

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