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

Beyond the annotations (which already indicate non-idempotent and non-read-only), the description adds critical behavioral details: the flip is applied in-place, calling twice reverts the animation, frame count/order are preserved, and the return shape is { jobId, mirrored }. It also mentions cost ('FREE, no AI'), which is useful context not in annotations.

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 front-loaded with the critical info ('FREE, no AI'), then explains the action, the idempotency gotcha, the frame preservation, the alternative, and the return value. Every sentence earns its place; nothing is wasted or redundant.

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?

Given the absence of an output schema, the description explicitly states the return object and polling mechanism. It also covers the non-idempotency hazard and the workflow for keeping both directions. This makes the tool fully understood without needing extra documentation.

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?

The schema already documents both parameters with clear descriptions (animation slug, character id) at 100% coverage. The description adds context about the effect on the animation (in-place, frame preservation) but does not introduce new parameter-level semantics beyond the schema, so the baseline of 3 applies.

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 uses a specific verb ('flip every cached frame') and names the resource ('ONE animation'), clearly distinguishing it from siblings like duplicate_animation. It also gives a concrete use case ('get walk_left from walk_right'), making the tool's purpose immediately obvious.

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 explicitly warns about non-idempotency ('call it once and check the result before calling again') and provides an alternative for preserving both directions ('call duplicate_animation first and mirror the copy'). This is direct when-to-use and when-not-to-use guidance.

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