layer_fill

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

With no annotations, the description carries the burden and does disclose one real behavioral trait: the change is snapshot-undoable, which tells the agent it can be reversed. It does not cover permissions, interaction with layer alpha/transparency, or failure behavior, leaving notable gaps for a mutation tool.

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?

A single compact sentence with the primary action front-loaded and the no-selection fallback appended. 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?

An output schema exists, so return values need not be described, and the undo note plus targeting rule cover the core behavior. However, for an unannotated mutation tool with 0% schema coverage, the missing parameter documentation and error/permission context leave it only partially complete.

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 0%, so the description must compensate for all three parameters. It only adds meaning for color (CSS/Gegl format, default black implied); layer_id and session_id go completely unexplained in both schema and 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?

States a specific verb (fill) and resource (selected area of a layer) plus the fallback scope when no selection exists. An agent can immediately tell what the tool does, and no sibling tool overlaps this fill operation.

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 a conditional behavior (fills selection if present, whole layer otherwise), which implicitly guides usage, but it never states when to choose this over alternatives like shape_create or filter_apply, nor any prerequisites such as an active session or layer.

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