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

With no annotations, the description carries the full burden and does well: it discloses the paid-key requirement, a per-call credit cost ('costs one icon'), the return value ('download URL for the edited transparent PNG'), and the per-call change limit. It stops short of error modes or what happens when the edit fails, which keeps it from a 5.

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-loaded with the purpose, then usage and rules of thumb in a compact block; the sentence about describing end state versus removal is genuinely load-bearing. Slightly dense, but no sentence is 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 two-parameter mutation tool with no output schema and no annotations, the description covers auth, cost, expected return, editing constraints, and the downstream workflow step (adding the result to '## Icons' in CLAYCUT.md). 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 baseline is 3, but the description adds real meaning: image_url accepts a Claycut asset URL or any public PNG, and instruction should describe the end state to draw rather than what to remove, plus a three-change cap that the schema's maxLength does not convey.

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 first sentence states a specific verb and resource ('Change one thing about an icon') and immediately frames the scope ('keeping everything else as it is'), which is the defining characteristic versus a full regeneration. It names the sibling generate_app_icon explicitly, so an agent can route between them without opening either 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?

Explicit when-to-use ('when the user likes an icon but wants a detail fixed') and when-not ('a new generation redraws the whole object and loses what they liked'), naming the alternative tool. It also gives operational rules: up to three changes, always edit the original not a previous edit, and name what must not change.

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