Extract a frame

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

With annotations present (readOnlyHint=false, destructiveHint=false, idempotentHint=false), the safety profile is mostly covered by structured data. The description usefully adds the external ffmpeg dependency and that a PNG is written to disk, but says nothing about overwrite behavior when outFile already exists or any auth requirement despite login tools being siblings.

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?

A single tight sentence front-loads the action, its inputs, its output format, the motivation, and the dependency—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?

For a 4-param, no-required, no-output-schema tool, the description covers source, output artifact, position, and the ffmpeg prerequisite. The only real omission is what the tool returns (e.g. the written path) and conflict behavior on existing files.

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. The description restates the position values ('last, first or at N seconds') that the schema already defines, and adds no format or default detail beyond it.

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?

Names a concrete verb (save/extract) and resource (one frame as PNG), specifies the two source kinds (local video or finished job) and the three position modes. No sibling tool does frame extraction, and the output format is explicit.

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 clause 'e.g. to start the next scene from it' implies the intended workflow (feeding a sequence), but there is no explicit when-to-use/when-not guidance and no naming of alternatives such as download_job or sequence_start.

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