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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower. The description adds real value beyond them: it is free (no render debit, no LLM), output is bounded to 640px, and it explicitly is not an approval. These cost/output traits are exactly the kind of context annotations cannot express.

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?

Three tight sentences, front-loaded with the core action and bounded output size. The 'No LLM, render debit or full free movie' clause is slightly compressed/awkward but still economical; no filler.

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?

An output schema exists so return values need no explanation, and annotations carry the safety profile. However, with two required, zero-coverage parameters, the definition leaves parameter meaning unaddressed, which is the main completeness gap for an otherwise simple preview tool.

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?

Both parameters have 0% schema description coverage, so the description carries the burden. It only implies that revisionId refers to a 'saved revision' and gives no meaning for projectId, nor the relationship between the two. It does not compensate for the undocumented 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+resource: 'Generate a free bounded first-frame image of this exact saved revision, maximum 640px long side.' The negative statements ('Preview is not an approval or a priced render') implicitly separate it from confirm/quote siblings, though no sibling is named explicitly.

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 description implies usage (a preview before approval/priced render) and rules out misreading it as an approval or paid render, but never states when to call it versus alternatives like studio_motion_confirm, studio_motion_quote, or studio_motion_create. Usage is implied rather than explicit.

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