Extract a frame

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, but the description adds valuable behavioral context: 'Answers immediately. Seeking is done before decoding, so grabbing a frame from an hour-long file costs the same as from a short one.' This explains performance characteristics beyond the structured metadata.

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?

The description is compact and well-structured: one sentence for the core action, one for performance, and two for use cases. Every sentence adds value with no redundancy or 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 read-only extraction tool with full schema coverage, output schema present, and annotations, the description covers the essential aspects: what it does, when to use it, and performance expectations. It is fully sufficient for an agent to select and invoke the tool correctly.

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%, and every parameter has its own description in the schema. The tool description does not add any additional meaning about parameters, but since the schema already fully documents them, the baseline of 3 is appropriate.

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?

The description opens with 'Save a single frame as an image so it can actually be looked at,' which precisely states the tool's action and purpose. It clearly distinguishes from siblings like extract_filmstrip by emphasizing 'single frame' and the goal of visual inspection.

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?

It provides explicit use cases: 'Use it to check what is in footage before cutting, and to confirm a render looks the way it was meant to.' These are concrete scenarios, though it does not mention any alternatives or exclusions, so it falls short of a full 5.

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