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', i.e. repeated identical calls have no additional effect, while the annotations declare idempotentHint=false. That is a direct conflict about retry safety and could lead an agent to skip the idempotency_key. It does add genuinely useful behavior (the returned slug), so this is a partial rather than total contradiction, but the mismatch is material.

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, zero filler, and the core action is front-loaded before the return-value and dedupe notes. Every clause carries information an agent needs.

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 4-parameter mutation with no output schema, the description covers the creation effect, the private scope, the returned slug, and dedupe behavior, which is most of what is needed. It is short of complete because it never addresses permissions/ownership of a private list or how the dedupe window interacts with the optional idempotency_key.

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 the strong 'usually omit' guidance for category. The description adds no parameter-level meaning beyond the schema; 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?

Specific verb + resource + scope: 'Create a new private list' tells the agent exactly what is produced and that the result is private (versus publish_list, which exposes it). It also names the downstream consumer (add_item), so the agent understands where this fits in the workflow without opening another 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?

Usage is implied rather than stated: the agent learns to create the list and then reuse the slug in add_item, but there is no explicit 'use this instead of X when Y', no prerequisite (e.g., must be signed in), and no guidance on when to prefer update_list or archive_list. Adequate but leaves the routing decision to inference.

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