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

Annotations carry the safety profile (destructiveHint=true, readOnlyHint=false, idempotentHint=true), and the description adds genuinely new behavioral context: the best-effort race condition where an already-finishing run may still complete, plus the instruction to follow llmContext guidance in results. No contradiction with annotations — the best-effort note is consistent with idempotentHint=true.

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?

Two sentences with the action and scope front-loaded, the sibling disambiguator in a tight parenthetical, and the best-effort caveat immediately after. The llmContext instruction is short and non-redundant with the schema or annotations; no filler survives.

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?

The output schema covers return values, annotations cover the destructive/idempotent profile, and the schema covers all three parameters, so the description only needed to handle applicability and edge behavior — which it does via the queued/in-flight scope and best-effort disclosure. Minor gap: it doesn't discuss downstream effects of canceling (e.g., dependent runs or webhook notifications), but nothing critical is missing for this complexity.

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 the baseline of 3 applies. All three parameters (runId, environment, workspaceId) are already documented with provenance ('The run ID from run_workflow') and validation rules ('Must match a granted target from get_me'), so the description need not add parameter detail.

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') and a precise resource ('a queued or in-flight workflow run'). The parenthetical '(workflows group)' disambiguates it from sibling cancelers cancel_classify_run, cancel_extract_run, and cancel_split_run, and the cancel-vs-delete verb distinction separates it from delete_workflow_run without opening any 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 'queued or in-flight' qualifier gives clear context for when this tool applies, and the best-effort caveat ('a run already finishing may still complete') marks the applicability boundary. However, it never explicitly names alternatives (e.g., delete_workflow_run for finished runs) or states when not to cancel, so some routing is left to inference.

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