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

Annotations already declare idempotentHint=true and destructiveHint=true, so the safety profile is partially covered. The description adds valuable behavior beyond that: it is a partial update ('Changes only the fields named in updateFields') and it uses optimistic concurrency via expectedVersion with a mismatch-retry policy. It stops short of describing what 'destructive' means here (e.g. field clearing), which the schema's updateFields description covers instead.

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?

Front-loaded with the core action, then scoping, then the concurrency/error contract. Each sentence earns its place: field list, partial-update rule, parameter sourcing, mismatch recovery, and scope exclusion.

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 mutation tool with no output schema, the description supplies what the annotations cannot: partial-update semantics, the concurrency token contract, and a safe error-recovery rule. Combined with the fully documented schema, an agent has everything needed to invoke it correctly.

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 the baseline is 3. The description adds meaning beyond the schema by clarifying that only keys named in updateFields are applied and by specifying that listId/expectedVersion come from the latest library_list_get, reinforcing the optimistic-concurrency contract.

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 ('Change one existing item in an owned Library List'), enumerates the mutable fields, and gives a concrete example ('to check it off'). It also explicitly excludes the adjacent sibling by scope ('Library Lists only, not trip checklists'), so an agent can distinguish it from checklist_item_update.

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 workflow guidance: 'Use the listId and expectedVersion from the latest library_list_get' and a recovery path for 'library_version_mismatch' ('read the list again and reconsider the change; never retry blindly'). It also names the boundary condition against trip checklists. When-to-use and error handling are both present.

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