Paint: Write single pixels

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

Annotations already establish the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false), so the bar is lower. The description adds real behavior beyond them: writes are exact with no blending (existing pixels are overwritten, alpha does not composite), and undo applies uniformly across drawing tools, which reassures the agent about reversibility.

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 short paragraphs, front-loaded with the exact-write/no-blend semantics before the targeting details. The pixel-format examples are mildly redundant with the schema, keeping it out of 5 territory.

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 5-parameter mutation tool with no output schema, the description covers canvas targeting, layer selection, pixel payload semantics and undo, which is most of what an agent needs. It is silent on the preview/preview_size reply behavior, though the schema describes those fields.

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 80%, so the schema already documents canvas, layer, pixels, preview and preview_size. The description's restatement of the three pixel payload shapes mirrors the anyOf union in the schema and adds no format detail beyond it; baseline 3 is appropriate.

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 ('Exact pixel writes') and immediately qualifies it with 'no blending', which tells the agent it is a raw overwrite rather than a blend-capable brush. It implicitly separates itself from blending siblings like paint_brush/paint_fill, but never names an alternative tool, so it falls short of a 5.

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?

'Use for pixel art and small fixes' gives clear usage context, and it notes the canvas must be created with paint_canvas. However, it never states when to prefer a sibling primitive (paint_rect, paint_fill, paint_line) instead, so the when-not guidance is only implied.

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