fill_parts_on_slot

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

Since no annotations are provided, the description carries the full burden. It discloses that the base body is never modified, that it performs a 'flat local fill only' (no shading), and that it uses the character part map. It also forbids external image generators. These are non-obvious behavioral traits beyond the tool's basic function, making it highly transparent.

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 longer than average but every section adds value: it starts with the core purpose, then lists parameter semantics in bullet format, then gives usage guidance and restrictions. The structure is front-loaded and scannable. It could be slightly tighter, but the detail is justified given the tool's complexity.

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?

Despite 9 parameters and no annotations, the description covers the essential operational context: default behavior, parameter formats, sibling alternatives, shading caveats, and prohibited actions. An output schema is present, so return values are covered. An agent has enough information to invoke this tool correctly and safely in the wider pipeline.

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. It explains the key parameters: parts (with naming examples), part_ids (as integer ids from get_part_ids), color (hex or RGBA array), and part_colors (object with overrides). It also explains Omit behavior. However, it leaves scale, plan_id, and output_dir undocumented, though these are likely secondary. The main parameters are covered well.

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 opens with a clear verb-resource pair: 'Fill body-part silhouettes onto design/layers/<layer>.png'. It explicitly states the tool replaces Shell/PIL scripts and names the mechanism (character part map), making its purpose unmistakable and distinct from sibling tools like fill_rect or paint_pixels.

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 explicit when-to-use guidance: it specifies that for shading one should 'use plan_shading + paint_* after outfit paint' and for adding details use 'fill_rect / draw_line / paint_pixels'. It also explains the default behavior when parts/part_ids are omitted and flags forbidden actions (Shell scripts). This gives clear direction against alternatives.

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