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

Adds real context beyond annotations: it is free (no credits) and returns image_id, image_url, and zu_dunkel. The zu_dunkel warning tells the agent to avoid animating from a black frame, which is behavioral guidance not present in annotations.

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?

Four short sentences, front-loaded with purpose, then usage, then a caveat, then the free-cost note. 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?

Covers purpose, usage, return fields, cost, and a key failure mode (too dark). With only 2 params and 100% schema coverage, this is nearly complete; a brief note on whether the source clip must be finished/exported might help, but it is strongly implied.

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 schema already documents video_id and scene_ref. The description adds no syntax or format detail for the parameters beyond what the schema provides. 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?

States a specific verb and resource ('Extract the LAST frame of a finished clip as a new image') and names the output fields. Distinguishes itself from siblings like lab_render_frames by emphasizing the last frame specifically.

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?

Explicitly says when to use it ('continue one unbroken take, or as a still') and names the alternative path (lab_verkettung) that handles this automatically for uebergang=durchgehend, so the agent knows when NOT to call it.

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