cancel_runCancel a running code execution in the MCE sandbox by providing its run ID. Stops further work; note that already completed external effects remain.
Request cooperative cancellation; completed external effects cannot be undone.
| Name | Required | Description | Default |
|---|---|---|---|
| run_id | Yes | Caller-owned persistent run identifier. |
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Changes observed during successful MCP inspections.
v2.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only provide readOnlyHint=false, so the description carries the burden of behavioral disclosure. It adds meaningful context: cancellation is cooperative and completed external effects cannot be undone. This is useful nuance beyond the annotation.
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?
The description is a single concise sentence that front-loads the action and then attaches the critical caveat. Every word earns its place.
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 tool with an output schema and a readOnlyHint=false annotation, the description covers the key behavioral caveat. It does not specify what happens if a run has already completed or how the result is reported, but the output schema likely covers the latter.
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 run_id is already described as a 'Caller-owned persistent run identifier'. The tool description adds no extra parameter meaning, so the baseline of 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?
The description states a specific action, 'request cooperative cancellation', and the title/name identify the resource as a run. It adds useful nuance about completed external effects being irreversible. It does not explicitly contrast with sibling tools, but the purpose is still unambiguous.
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 is given on when to use this tool versus alternatives such as get_run, or when cancellation may be inappropriate. The caveat about completed effects implies some caution, but it does not explain conditions or provide routing.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.