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

Without annotations, the description carries the full burden. It accurately describes the return value (presigned PUT URL) and the optional preview behavior. It does not mention potential side effects (e.g., creating a pending upload record) but otherwise is transparent about observable behavior.

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?

Two concise sentences with no redundancy. The core action, optional behavior, and follow-up are all included without unnecessary detail.

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 no output schema, mentioning that the call returns keys and that finalize_upload should be called next provides adequate context for a caller. It lacks error scenarios or caveats, but the essential workflow is complete enough for basic usage.

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 provides types, defaults, and constraints for all three parameters. The description adds meaning to withPreview (PNG preview) but does not elaborate on filename or contentLength. Since schema coverage is high, the baseline is 3; the description adds only minimal extra semantic detail.

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?

Clearly states the primary function: returns a presigned PUT URL for a .glb file, optionally with a PNG preview. Also indicates the follow-up action (call finalize_upload), so the caller understands the tool's role in the upload workflow.

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 'For clients that can upload bytes' identifies when this tool is appropriate, and the instruction to call finalize_upload afterward provides a usage sequence. It does not explicitly contrast with sibling tools, but the context is sufficient for a typical caller.

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