rent.dev

Extend a sandbox

rent_extend_sandbox

Idempotent

Sets a running sandbox to stop timeout_s seconds from now (at most 86400), holding the added cost first on the key that started it; a short balance answers 402 with top-up links. An API key with a spend limit cannot extend a sandbox another key started (403 forbidden).

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "sandbox_id": "<sandbox_id>",
      "timeout_s": "<timeout_s>"
    },
    "name": "rent_extend_sandbox"
  }
}

Input Schema

Name	Required	Description	Default
`timeout_s`	Yes
`sandbox_id`	Yes	Sandbox id (`lse_…`) from rent_create_sandbox or rent_list_sandboxes. It names the sandbox for its whole life and keeps answering rent_get_sandbox, with the final state, after it ends.

Output Schema

Name	Required	Description	Default
`id`	Yes
`wire`	Yes
`state`	Yes
`domain`	Yes
`region`	Yes
`ended_at`	Yes
`metadata`	Yes
`supplier`	Yes
`template`	Yes
`billed_by`	Yes
`cpu_count`	Yes
`memory_mb`	Yes
`account_id`	Yes
`auto_pause`	Yes
`created_at`	Yes
`sandbox_id`	Yes
`started_at`	Yes
`timeout_at`	Yes
`auto_resume`	Yes
`endpoint_id`	Yes
`held_micros`	Yes
`captured_micros`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 12, 2026

TDQS

A4/5.0

Behavior5/5

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

Beyond the annotations, the description discloses billing behavior (added cost is charged first to the key that started the sandbox), the 402 short-balance response with top-up links, and the 403 ownership constraint. These are exactly the operational facts an agent cannot get from readOnlyHint/destructiveHint/idempotentHint, and the absolute-deadline wording is consistent with idempotentHint=true.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two dense sentences with no filler, and the core semantics (new stop time) come first, followed by cost and error behavior. The billing clause is slightly compressed into an awkward phrase ('holding the added cost first on the key that started it'), but nothing is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With rich annotations and an output schema, the description only needs to cover side effects and failure modes, which it does (billing, 402, 403). The one gap is the absence of guidance on behavior toward non-running or already-terminated sandboxes, which matters for an openWorldHint tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 50%, and the description compensates by clarifying that timeout_s is a relative offset in seconds from now (an absolute deadline, hence idempotent) rather than an increment, and repeats the 86400 ceiling. The sandbox_id meaning is already fully documented in the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a concrete verb and resource: it 'sets a running sandbox to stop timeout_s seconds from now', which is unambiguously an extension of a sandbox's lifetime. It does not explicitly name sibling tools (pause/resume/terminate) for contrast, so differentiation is inferred from the verb rather than stated.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Preconditions are implied ('a running sandbox') and one hard exclusion is stated (a spend-limited key cannot extend a sandbox another key started, returning 403). However, there is no explicit guidance on when to extend versus pause, resume, or terminate, and no note on the effect of extending an already-long deadline.

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

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