Stop a running Temporal workflow execution by its workflow ID. Use it to halt a specific workflow that is no longer needed.
Cancel a running workflow execution
| Name | Required | Description | Default |
|---|---|---|---|
| namespace | No | Temporal namespace for this operation; omit to use the server default | |
| workflow_id | Yes | The workflow execution ID to cancel |
Changes observed during successful MCP inspections.
v1.10.1Input schema / properties / namespaceAdded value: +{
+ "description": "Temporal namespace for this operation; omit to use the server default",
+ "enum": [
+ "default"
+ ],
+ "minLength": 1,
+ "type": "string"
+}v1.9.0v1.5.0v1.3.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden and falls well short. It does not explain that cancel is a cooperative/graceful request that the workflow may handle or ignore (as opposed to terminate's forced stop), nor reversibility, permissions, or required state.
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?
A single, front-loaded sentence with zero filler. It is efficient, though the terseness is partly a symptom of what is missing rather than pure economy.
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 mutating operation with no annotations, no output schema, and a sibling that does a similar-but-different thing, the description should clarify cancellation semantics and the cancel-vs-terminate distinction. It leaves an agent unable to call this correctly with confidence.
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 parameters are already documented in the schema. The description adds no syntax, format, or constraint detail beyond the schema, which is the baseline-3 outcome when the schema does 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 (cancel) and resource (workflow execution), so the agent knows exactly what the tool does. However, it does not differentiate from the highly similar sibling terminate_workflow, which an agent must choose between.
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?
No guidance on when to use cancel_workflow versus terminate_workflow, batch_cancel, or cancel_activity. The description gives no prerequisites, no conditions, and no alternatives despite a sibling set full of near-duplicates.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.