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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real behavioral context beyond them: that zero is a valid timecode, that region renders at a higher resolution rather than upscaling the frame, and that the output image takes the region's shape. It stops short of describing pagination or the concrete return format.

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 short sentences, each carrying distinct load: what it captures, how to get detail, and the anti-pattern to avoid. The task and its constraint are front-loaded with 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 four-required-parameter tool with no output schema, the description covers purpose, the undocumented timecode param, region/longEdge interaction and the sibling alternative. Only a brief note on the returned image format/type is absent, which is a minor gap rather than a blocking one.

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 75% and notably the required `timecode` parameter has no schema description at all; the description compensates by defining its unit and edge case ('in seconds. Zero is valid.'). It also adds the rationale and interaction for region/longEdge (why to pass region, that it raises effective resolution) beyond what the schema states, going past the baseline 3.

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 ('Capture one composed frame'), scopes it to 'a known timecode in seconds', and explicitly distinguishes itself from the two sibling preview tools by naming preview_range as the contact-sheet alternative. An agent can route correctly without opening another schema.

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?

Gives positive guidance (pass region to inspect small text, logos, thin lines, edges; longEdge sets size) and an explicit negative exclusion ('Do not loop over this to imitate a contact sheet; use preview_range'). This is exactly the when/when-not/alternative structure the dimension asks for.

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