fill_tile

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

Annotations already declare this is not a read-only operation and is not open-world. The description adds meaningful context by stating that all of the tile's area is written and that the return value reports the filled pixels rather than merely call success.

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 short and front-loads the purpose in the first sentence. The second sentence explains the return value and is useful, though slightly more verbose than strictly necessary.

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, and the description does provide some return-value context. However, for a five-parameter mutation tool with only 20% schema description coverage, it leaves most parameter semantics unexplained and is not complete enough for reliable invocation.

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 only 20%, with just the frame parameter documented. The description implies color is a solid colour and that tile_index identifies the existing tile, but it does not explain filename, layer, tile_index, or frame semantics.

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 verb and resource: 'Fill an existing tile's artwork with a solid colour.' This distinguishes it from layer-level or tilemap-level fills, though it does not explicitly name the sibling tools it differs from.

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 when-to-use guidance, no prerequisites, and no comparison to alternatives such as fill_layer, fill_tilemap, or paint_tile_pixels. It only implies that the tile must already exist.

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