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

Annotations already declare idempotentHint=true, but the description explains the mechanism behind it: a caller-generated itemId reused on retries so a retried call never duplicates. It also discloses the version-mismatch failure mode and the required recovery behavior, which annotations cannot convey.

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?

Four compact sentences, all front-loaded on the action, and each one carries distinct, non-redundant information (purpose, idempotency, sourcing, error handling, scope). 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?

No output schema exists, but the description covers the full contract an agent needs: which ID/version to supply, how to retry safely, how to react to version mismatch, and what this tool explicitly does not touch. Nothing essential 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 baseline is 3, but the description adds cross-tool provenance for listId and expectedVersion ('from the latest library_list_get') and the 'latest' qualifier on expectedVersion, which clarifies freshness expectations beyond the schema text.

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 plus scope: 'Add one item to an owned Library List.' The singular 'one item' plus the explicit 'Library Lists only, not trip checklists' distinguishes it from the plural sibling library_list_items_add and from checklist_items_add.

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 explicit preconditions ('Use the listId and expectedVersion from the latest library_list_get'), an error-recovery path ('On library_version_mismatch, read the list again and reconsider the change; never retry blindly'), and a scope exclusion ('not trip checklists'). This is when/when-not/alternative guidance at a high level of specificity.

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