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

Beyond the destructiveHint=true annotation, the description discloses concrete behavior: the tool only affects not-yet-started requests, it is a *request* (202 CANCELLATION_REQUESTED, not a synchronous kill), and it names the underlying endpoint. This is useful context on force/semantics that annotations alone do not convey.

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 purpose, then return behavior, then the upstream endpoint. No filler or repetition; every sentence carries information.

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, the description usefully states the 202/CANCELLATION_REQUESTED response, and eligibility plus target are covered. It omits failure behavior (e.g., what happens if the request already started or the id is unknown), which is a minor but real gap for a mutation tool.

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 both model_id and request_id are already documented with format examples ('fal-ai/flux/schnell', queue request id). The description adds nothing param-specific, so the baseline 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?

States a specific verb+resource (cancel a request) and immediately narrows scope to 'queued (not-yet-started)', which is the key disambiguator versus siblings like falai_get_request_status or falai_get_request_result. An agent can identify the operation and its applicability 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?

The qualifier 'queued (not-yet-started)' tells the agent when cancellation is eligible, which is real usage guidance. However, it never names what to do when the request has already started, nor points to an alternative sibling, so the guidance is implied rather than explicit.

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