Extend the frame sideways

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

Annotations already declare readOnlyHint=false, openWorldHint=true and idempotentHint=false, so the mutating/non-reproducible profile is covered. The description adds a genuine behavioral fact not in the annotations ('Costs GPU time'), but says nothing about the required confirmation, irreversibility, or waiting behavior that all live only in the schema.

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?

Three short sentences, front-loaded with the core action, then a use case, then the cost caveat. No filler, though the third sentence is terse enough that it could carry a bit more behavioral weight.

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 an 8-parameter, open-world generative mutation with no output schema, the description covers what the tool does, why to use it, and that it consumes GPU time. Since the schema fully documents parameters including the mandatory confirm flag, the remaining omissions (return shape aside) are minor.

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 100%, so every one of the 8 parameters (including confirm, speed, fraction, wait) is already fully documented in the schema. The description only loosely gestures at 'direction' via 'in a direction' and adds no syntax or defaults beyond it, so baseline 3 is appropriate.

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 ('Extend one image in a direction') and clarifies the generative nature ('inventing what lies beyond the current frame'). This distinguishes it from a plain regeneration, but it never contrasts itself with the closest sibling, zoom_out, so the agent must infer which extending operation to pick.

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?

Gives a concrete use case ('turning a portrait crop into a wide shot without regenerating it'), which tells the agent when this is the right tool. It offers no exclusions or explicit alternative tool, so it falls short of the 5 band.

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