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

Annotations already cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the description earns credit for adding the 422 no-op-reject on terminal exports and the source of the exportId. It could say more about what happens to partial output artifacts or whether the cancel is reversible, but the error semantics are a genuine addition.

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 clauses, front-loaded with the action and scope, followed by required inputs and then the failure mode. No filler, no restatement of the 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?

For a 2-param mutation with no output schema but full annotations, the description covers scope, prerequisites, and the terminal-state error. Minor gaps remain around post-cancel state or partial-artifact cleanup, but nothing an agent needs to invoke it correctly is missing.

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% and both parameters are documented as path params, so the baseline is 3. The description adds only the provenance hint ('from the export enqueue'); no format or validation detail beyond the schema.

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 (cancel) plus a precisely bounded resource: an in-flight NLE export limited to fcpxml/premiere. The parenthetical scoping distinguishes it from the cluster of nearby cancel_* siblings (cancel_compose, cancel_render, cancel_job) well enough for an agent to pick correctly.

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 gives prerequisites (projectId + exportId, with exportId sourced 'from the export enqueue') and a state condition ('in-flight', 422 if already terminal), which tells the agent when the call is valid. It stops short of explicitly contrasting itself with cancel_render/cancel_compose/cancel_job, so the alternative-selection guidance is inferential rather than stated.

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