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

Beyond the annotations, it discloses non-obvious behavior: the source photo is left untouched and the call restores it, so the result carries a NEW image id, plus the full processing pipeline (find subject, cut on a copy, add border, add shadow unless shadow is false, crop with room, keep transparency). This is consistent with destructiveHint=false and readOnlyHint=false and adds genuinely useful context.

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?

Purpose and output are front-loaded, and the pipeline/constraint sentences each carry real information. It is slightly long and repeats schema-level default values (border, border_color, shadow), which keeps it from a 5.

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?

With no output schema, the description still explains the return value (a transparent PNG/WebP download link plus the new image id), the destructive/restore behavior, the layer-count constraint, and the rotated-subject edge case. An agent has everything needed to invoke it 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 coverage is 100%, so the schema already documents all six parameters with defaults and enums. The description mostly restates these (border default 2.5% of the subject's long side, border_color #ffffff, format keeps transparency) and only marginally extends meaning via the subject_up orientation hint, so the baseline 3 applies.

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 a precise verb+resource: cut the subject out as a die-cut sticker and return a transparent PNG/WebP download link. The output (bordered, shadowed die-cut sticker) is unmistakably distinct from the sibling generative tools (make_meme, make_grid, make_carousel, make_story), so no confusion is possible even without naming an alternative.

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 gives clear preconditions and context — the image must have a single layer, the selection service is required, and subject_up should be set when the subject is not upright — which tells the agent when the call will work. It never states when to prefer this over a sibling or any exclusion cases, so it stops short of a 5.

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