fill_region

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

With no annotations provided, the description carries the transparency burden. It discloses that tile ID 0 clears, and more importantly, explains that autotiles are placed as base variant (P1) only, requiring apply_autotile for smart edges. This is non-obvious and valuable. It does not mention side effects like overwriting, but for a fill operation the behavior is clear.

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 three concise sentences, each adding distinct information: the core operation, the clear behavior, and the autotile caveat. It is front-loaded with the verb and resource, with no wasted words.

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?

Given the tool's simplicity and the existing schema, the description combined with the schema covers the functionality well: target map, layer, rectangle, tile ID, and special cases (clear, autotile). It also connects to apply_autotile for a complete workflow. Minor gaps remain around error conditions or coordinate formats, but these are not critical for a fill tool.

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 75%, with descriptions for rect, layer, and tileId, but mapId is undocumented. The description adds the autotile behavior note and restates clear behavior, but does not explain mapId or coordinate details. It adds marginal value over the schema without fully compensating for the missing parameter description.

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 clearly states the tool fills a rectangle of a layer with a single tile ID, and optionally the whole layer if rect is omitted. This distinguishes it from siblings like set_map_tiles (sets individual tiles) and scatter_tiles (random placement), and the mention of whole-layer fill adds useful scope.

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 provides clear context for when to use this tool (rectangular fill, whole-layer fill) and directly references the apply_autotile tool for achieving smart edges with autotiles, which is a relevant alternative/next step. It does not explicitly list exclusions for other tile-placement tools, but the guidance is sufficient.

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