Fetch one region crop

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds that the crop is returned at higher resolution, which is useful context, but says nothing about the maxTokens-capped return or what happens when captureId is omitted beyond the schema note.

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?

Two tight sentences with zero filler; the core action is front-loaded before the region-form detail.

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?

No output schema exists, and the description never indicates what comes back (an image crop consumed as tokens, presumably governed by maxTokens). Combined with the un-explained label parameter, an agent has to infer the return contract.

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 50%, so the description must compensate. It does clarify the dual form of region and its provenance from ui_diff, which the schema's anyOf does not express, but label and the defaulting behavior of captureId/maxTokens are left entirely to the schema.

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 ('Fetch a single crop from a stored capture') plus a key differentiator ('at higher resolution'), which separates it from a full capture. It does not explicitly contrast with ui_capture, so sibling differentiation is only partial.

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?

Usage is implied through the region provenance note — 'a diff region index (from ui_diff output)' — which tells the agent this follows a diff workflow. There is no explicit when-to-use vs when-not guidance or statement of alternatives such as ui_capture.

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