Lay out drafts side by side for comparison

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

With no annotations, the description carries the full behavioral burden and does disclose two non-obvious traits: no text is drawn onto the image, and the result is a position-to-file mapping rather than baked-in labels. It omits overwrite behavior, error conditions, and how output_path conflicts are handled, so the mutation side is under-disclosed.

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?

Two sentences, both earning their place, with the core action front-loaded and the return-format caveat second. No filler or restated title.

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?

With no output schema and no annotations, the description appropriately covers the return value (position-to-file listing in reading order) and the 12-image ceiling. Remaining gaps are minor: side effects of the required output_path and overwrite are left implicit.

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%, so most parameters are already documented ('roughly square grid' default for columns, example output path). The description's 'up to 12' merely restates maxItems:12 and it says nothing about columns or overwrite, adding little beyond the schema. Baseline 3 fits.

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 and resource — putting up to 12 draft images onto a single grid — and names the concrete upstream source (image_generate directions) that produces the inputs. An agent can tell this apart from compose/deliver/media_optimize siblings without opening the schema.

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?

Clearly says when this tool applies: judging several drafts against each other rather than one at a time. It does not name an alternative to use instead when comparison isn't the goal, so it stops short of full routing.

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