Extend a running sandbox's lifetime by adding seconds to prevent automatic termination when it reaches its max-duration cap.
Extend a running sandbox's wall-clock lifetime by N seconds so it isn't auto-terminated at its max-duration cap.
| Name | Required | Description | Default |
|---|---|---|---|
| session_id | Yes | The sandbox/session ID to extend. | |
| additional_duration_seconds | Yes | Extra lifetime to add, in seconds (sent as a Duration string, e.g. 3600s). |
Changes observed during successful MCP inspections.
v0.3.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already signal readOnlyHint=false and idempotentHint=false. The description adds useful behavioral context: it affects wall-clock lifetime, applies only to running sandboxes, and prevents auto-termination at the max-duration cap. This goes beyond the bare annotations without contradicting them.
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 sentence that front-loads the core action and the motivating outcome. Every word contributes meaning; there is no fluff or repetition.
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 simple two-parameter operation with no output schema, the description provides the operation, the precondition (running sandbox), and the purpose (avoid auto-termination). It could mention return behavior or limits on extensions, but nothing critical is missing.
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. The tool description itself doesn't add parameter-level detail, but the schema already defines both session_id and additional_duration_seconds adequately. The 'Duration string' wording in the schema is slightly ambiguous, but that's a schema concern, not a description gap.
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 uses a specific verb ('Extend'), a specific resource ('a running sandbox's wall-clock lifetime'), and a clear intended outcome ('so it isn't auto-terminated at its max-duration cap'). This clearly differentiates it from related operations like pause, resume, terminate, or generic update.
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 phrase 'running sandbox' and 'max-duration cap' gives clear context for when this tool should be used. It does not explicitly name alternatives or exclusions, but the use case is specific enough that an agent can infer when to invoke it.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.