Cancel a queued or scheduled task by task_id. Returns current status if already completed, failed, or cancelled; errors only for unknown task_id.
Cancel a queued or scheduled task. Idempotent — if the task is already completed/failed/cancelled this returns the existing status without error. Throws only if task_id is unknown.
| Name | Required | Description | Default |
|---|---|---|---|
| task_id | Yes | The id of the task to cancel. |
Changes observed during successful MCP inspections.
v0.16.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden and does well: it discloses idempotency, the no-error behavior for completed/failed/cancelled tasks, and the sole failure mode (unknown task_id). It omits permission/auth requirements and whether cancellation is reversible.
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 tight sentences, front-loaded with the action and its scope, followed by the exact error semantics. No filler.
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 one-parameter mutation with no annotations or output schema, the description covers the key agent concerns: eligible task states, idempotent return behavior, and the lone exception case. What it lacks is auth/permission context and any note on cancelling in-flight tasks.
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 the single parameter is fully documented in the schema. The description adds no meaning about task_id format or source beyond what the schema provides, 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 task) and narrows the eligible state to 'queued or scheduled'. It implies a single-task scope that separates it from cancel_all, but never names the sibling explicitly.
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 error/idempotency conditions give usable context, but there is no explicit when-to-use versus siblings like cancel_all, retry_task, or expedite_task. The single-task scope is only inferred from the wording.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.