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

Beyond the readOnlyHint=false/destructiveHint=false annotations, the description discloses non-obvious behavior: it COSTS CREDITS scaled 'by output resolution,' and it creates a NEW generation rather than editing in place, placed in the source's own project. Credit cost and new-artifact semantics are exactly the traits an agent needs and would not get from structured fields.

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?

Information is front-loaded with the core operation before cost, output semantics, and options. It is dense with parentheticals but nearly every clause carries actionable content; minor run-on structure keeps it from a 5.

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?

For a 7-param mutation tool with no output schema, the description covers cost, new-generation placement, and the key parameter interactions. It stops short of clarifying task/async behavior (siblings include get_task/cancel_task) or the returned handle, leaving a small gap.

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?

With 57% schema coverage, the description compensates usefully: it specifies extend defaults to all four, that zoom < 1 means zoom out, the asset_id/generation_id mutual exclusivity ('not both'), and that project_id applies only to asset_id while resolution defaults to the source's. This adds meaning beyond the schema for the undocumented params.

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 gives a specific verb and mechanism — 'outpaints an existing generation to a bigger canvas / new aspect ratio — the model extends the scene beyond the original edges' — which clearly separates it from generate_image (new content) and upscale_image (resolution, not canvas). An agent can identify the operation 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?

It explains practical usage contexts: restrict directions with extend, zoom out with zoom < 1, and using an uploaded asset as the base. However, it never names a sibling alternative (upscale_image, generate_image, cutout) or states when NOT to use this tool, so the routing guidance is implicit rather than explicit.

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