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

Annotations declare the write/idempotency profile, but the description adds the critical economics: this SPENDS CREDITS, preview is a costed dry run that creates no job, spends no credits and makes no provider call, and the effect prompt cannot be customized. Those are exactly the facts an agent needs before committing a paid mutation.

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 credit-spend warning in caps, then the constraint on customization, then the preview escape hatch. Nothing is padded and the most important risk is first.

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 partly covers returns by saying preview yields the credit price, and it covers the cost and customization constraints of a paid mutation well. It stops short of saying what a non-preview call returns (job handle, status URL, etc.), which is the remaining gap for a 7-parameter write 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?

Schema description coverage is 100%, so the baseline is 3; however the description adds useful framing that only three of the seven fields (effect, photo, duration) are real choices, implicitly classifying run_id, project and workspace as optional scoping metadata. It adds meaning but no syntax beyond 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 (render), a specific resource (a one-photo video effect) and names the sibling list_effects as the source of the slug. It is clearly distinguishable from render_video, render_image and render_audio by the 'one-photo effect' scope.

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?

Explains the operating model (the prompt is server-side and fixed; you only pick effect, photo, duration) and tells the agent to set preview:true for a costed dry run, which is a concrete usage rule. It does not, however, route between this tool and the sibling preview_render/preview_generation tools, so the alternative-selection guidance is incomplete.

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