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

Annotations already declare destructiveHint=true, readOnlyHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely new behavior: irreversibility ('cannot be resumed') and idempotency ('cancelling an already-cancelled workflow returns the same result'), which an agent needs for retry logic. It stops short of saying what happens to in-flight steps or whether cancellation is synchronous.

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 tight sentences, front-loaded with the action, followed by consequences and then the idempotency guarantee. Every sentence carries new information; nothing is repeated from the title or schema.

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?

An output schema exists, so return values need no explanation, and the description covers the key post-conditions: irreversibility, visibility in list_workflows, and exclusion from resume listings. A note on the effect on an in-flight workflow run would close the remaining gap.

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 coverage is 100% and the workflow_id property already documents its origin ('as returned by start_workflow') and recovery path via list_workflows. The description adds only 'by id', so baseline 3 is correct with the schema doing the heavy lifting.

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 ('Cancel an active workflow by id'), with the scope qualifier 'active'. The agent can immediately distinguish this from resume_workflow and list_workflows 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?

Explicitly routes the agent by naming siblings: cancelled runs are excluded from resume_workflow's active listing and remain visible in list_workflows. It does not state an explicit when-not case (e.g., cancelling a run that already completed), but the context provided is well above implied usage.

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