Draw a solid-color rectangle on a pixel art canvas by specifying position, dimensions, and color. Use it to add shapes or backgrounds programmatically.
Fill a rectangle with a solid color.
| Name | Required | Description | Default |
|---|---|---|---|
| x | Yes | Top-left X | |
| y | Yes | Top-left Y | |
| color | Yes | Fill color | |
| width | Yes | Rectangle width | |
| canvas | No | Canvas name | default |
| height | Yes | Rectangle height |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden of explaining behavior. 'Fill a rectangle with a solid color' communicates the core mutation, but does not disclose effects on existing pixels, canvas selection semantics, or coordinate/clipping behavior. A 3 is appropriate for minimal viable transparency.
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?
The description is a single, front-loaded sentence with no filler words. It directly names the action and the target resource, earning every word it uses.
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 simple drawing primitive, this is adequate alongside a fully described schema, but it lacks usage routing and behavioral caveats. The absence of annotations and an output schema means the description could add more context about effects and alternatives.
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 100%, so the schema already documents x, y, width, height, color, and canvas. The description only adds the concept of a solid-color fill, which does not meaningfully expand on the parameter semantics already present. 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 states a specific action and resource: filling a rectangle with a solid color. This clearly distinguishes it from sibling tools like set_pixel, draw_line, and clear, even though it does not explicitly name them.
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?
The description gives no explicit guidance about when to use fill_rect instead of set_pixel, draw_line, or clear. Usage is only vaguely implied by the tool name and the action described, not explained.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.