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

The description reveals a key behavioral constraint—the 10MB file size limit—and directs users to the appropriate fallback when that limit is exceeded. While it lacks details on success responses, failure modes (e.g., duplicate names), or overwrite behavior, the annotations (readOnlyHint: false, destructiveHint: false) already cover the read/write and destructive nature. The description adds meaningful behavioral context beyond the annotations, meriting a high score.

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 exceptionally concise—two sentences—with the action stated first and the size constraint and fallback immediately following. Every word contributes value; there is no padding or redundancy. The front-loaded structure makes the critical information immediately accessible.

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?

Given the tool's low complexity (one declared parameter, no output schema, no nested objects), the description is highly complete. It covers the primary action, the size threshold, and the alternative flow. The only missing element is the mechanism for providing the file content itself, but since the API endpoint is implied and the agent has sibling tools like createSandboxUploadUrl for context, the description adequately serves its purpose for most scenarios.

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?

The schema fully documents the sandbox_id parameter with a clear description, achieving 100% coverage of declared inputs. The description adds the file size context (10MB) but fails to address a critical undisclosed parameter: how the actual file content is transmitted (e.g., request body, multipart form-data). Since the schema only lists sandbox_id, an agent would be left guessing how to attach the file, preventing the description from fully compensating for this gap. The baseline of 3 is appropriate.

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 clearly states the exact action ('Upload a file directly to the sandbox'), identifying the specific verb (Upload), resource (file), and target (sandbox). It also distinguishes itself from sibling tools by explicitly defining a size limit (10MB) and referencing the alternate URL-based upload path, making its purpose 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?

The description explicitly states when to use this tool (for files up to 10MB) and when not to use it ('For larger files, use POST /v2/sandboxes/:sandbox_id/upload-urls'), providing a direct alternative. This gives the agent clear conditional logic for tool selection without needing to infer.

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