Fetch a keyframe image

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

The readOnlyHint annotation already establishes this as a safe read operation. The description adds that this is a real capture photo and suggests using it as photo evidence, which is useful domain context. However, it does not disclose response format, potential errors, or how the image data is returned.

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 two short sentences with no filler. It front-loads the core action and endpoint, then immediately provides the essential parameter provenance and the evidence-use context.

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 simple two-parameter image fetch, the description covers the endpoint, where to obtain the blob_key, and the intended use as evidence. The main gap is the implicit role of scan_id, and since there is no output schema, slightly more detail about the returned image could improve completeness, but the description is largely sufficient.

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?

The schema provides no descriptions for the parameters, so the description must compensate. It meaningfully explains that blob_key comes from scene detail keyframes[] refs, which is critical for invocation. However, scan_id is left completely unannotated and its relationship to the endpoint is not clarified.

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 clearly states the tool fetches a single capture keyframe as an image, names the endpoint, and identifies the blob_key as the target resource. It distinguishes real capture photos from synthetic views by explicitly saying 'Real capture photos,' which differentiates it from sibling tools like scene_synthetic_view_image.

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 description gives a clear precondition: blob_key comes from the scene detail keyframes[] refs. It also implies usage context by noting these are real capture photos to cite as evidence, but it does not explicitly name alternatives or state when not to use the tool.

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