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

Annotations only say readOnlyHint=false and destructiveHint=true; the description supplies the far more important behavior: a mandatory preview/confirm handshake, one-time token with 10-minute expiry, argument-change invalidation, duplicate-creation hazard, per-call token consumption, and data_availability semantics distinguishing no_rows/access_error from a true zero. It also adds a prompt-injection warning about result strings, which no structured field carries.

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?

Purpose and the no-retry warning are front-loaded, then the confirmation protocol, then result semantics. It is long but nearly every sentence carries operational weight; the trailing Korean billing note ("호출마다 토큰 1소진") is a language-inconsistent fragment, and the data_availability/prompt-injection block reads as shared boilerplate.

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 carries the return-value burden and does so by enumerating the five data_availability outcomes and warning that no_rows/access_error are not zero. Combined with the confirmation protocol and duplicate-creation guard, an agent has everything needed to invoke this write tool safely.

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, but the description adds real semantics the schema lacks: that confirmation_token must be paired with identical arguments, that omitting it yields a fresh preview, and that changing any argument invalidates it. It does not expand on channel_id or privacy_status beyond the schema, so it is not a 5.

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?

Opens with a specific verb+resource ("Create a new playlist on the selected channel") and immediately scopes the tool by stating what it cannot do (deletion happens in YouTube), which distinguishes it from sibling mutation tools like playlist__item__add or video__update. It never names an alternative sibling explicitly, so the differentiation is implicit rather than stated.

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 when-to-call, when-NOT-to-call ("Do not call again when the result is unknown - a second call creates a second playlist"), and a full two-step procedure with the condition for each step. It also states the exact user-agreement gate for supplying confirmation_token and what to do when arguments change, leaving nothing to inference.

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