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

Goes well beyond the annotations: it discloses that only cue text is translated while numbers, timing lines and headers are copied verbatim, that output is validated to re-parse to the same cues/timings or the call is refused unpaid, the underlying model, and the full billing model including that failed calls are not charged. This is unusually rich behavioral disclosure for a paid mutation-of-nothing compute call.

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 purpose, then behavior, then parameters, then price. Dense but every clause carries information; the pricing/payment sentence is the only part an agent might not strictly need for invocation, but it is relevant to call execution.

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?

Covers input format and size limit, output-preservation guarantees, failure behavior, model quality caveat, and cost/payment rails, and an output schema exists so return values need no explanation. Nothing needed to invoke this correctly 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 the baseline is 3, but the description adds the 50 KB size ceiling and identifies the body shape { subtitles, to, from }, reinforcing which fields are required and the payload limit. It adds real constraint information rather than restating the schema.

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 ('Translate an SRT or WebVTT subtitle file') and constrains the input format, which distinguishes it from the generic sibling `translate`. An agent can tell from the first clause exactly what this does and what it accepts.

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?

The format restriction (SRT/WebVTT) implicitly tells the agent when this tool applies versus plain `translate`, but there is no explicit when-to-use or when-not-to-use statement naming the alternative. Usage is inferable but not spelled out.

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