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

The description claims "Repeating the same request dedupes instead of creating another recent list," which describes idempotent replay behavior, while the annotation declares idempotentHint=false. That is a direct conflict on the single most consequential behavioral property of a create tool, so the agent cannot tell whether retries are safe. The note about returning the slug is useful, but the contradiction dominates.

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?

Two sentences, both front-loaded and load-bearing: one for the action and its return value, one for the retry/dedupe behavior. No filler, no restatement of the title.

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 output schema, the description correctly compensates by naming the return value (the slug) and its downstream use. What remains unaddressed is the retry story, which is genuinely ambiguous here, and any auth/ownership prerequisites for creating a private list.

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 title, category, subtitle, and idempotency_key are already fully documented — including curation guidance and the replay semantics of the key. The description adds no parameter-level meaning beyond what the schema states, 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 with scope modifier ("Create a new private list") and immediately names the follow-up tool (add_item), making it distinguishable from siblings like update_list, archive_list, and delete_list. An agent knows exactly what this does without opening the 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?

"return the exact slug to reuse in add_item" establishes the intended create-then-populate workflow and implicitly steers agents away from calling add_item before a list exists. It stops short of explicit exclusions, e.g. when to prefer update_list or an existing list found via find_lists/search_lists.

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