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

Annotations cover safety (readOnlyHint=false, destructiveHint=true, openWorldHint=true), so the bar is lower, yet the description still adds real context: it creates a new file, the source is left untouched in storage, and repeated crops do not compound. It does not address permissions or rate limits, but the behavioral picture is stronger than annotations alone.

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?

Front-loads the core action and result before justifying it. Four sentences is on the longer side, and the export-survival sentence is more rationale than instruction, but each sentence carries useful information rather than restating the name.

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, so the description must convey return behavior; it does so by stating the result is a new file placed in the slot. Combined with the originality note and parameter rationale, an agent has enough to invoke it correctly, though explicit sibling routing is absent.

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?

With 67% schema coverage, the schema documents most parameters, but the description adds genuine meaning for the ambiguous ones: `focus` as the surviving focal point and `maxWidth` as the guard against a 4000px photo filling a 400px card. It leaves `ratio` and `url` to the schema, which is acceptable.

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 ('Crop a picture to a shape, and/or shrink it'), immediately clarifying the result is a NEW file placed in the slot. This distinguishes it from siblings like edit_image_masked, set_image_display, and upload_image, which do not produce a cropped derivative file.

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?

Explains why cropping matters ('sections export to static HTML, so a crop that exists only as CSS ships uncropped'), which implies when to use it. However, it never names or excludes alternatives (e.g. edit_image_masked, set_image_display) or states prerequisites, leaving the agent to infer routing.

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