Start a media upload (step 1)

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

The description discloses the external PUT operation, no-credential requirement, short-lived URL, need for exact byte size, raw-bytes-only (no base64), and the draft-only capability restriction. These traits go far beyond what annotations (readOnlyHint=false, openWorldHint=true) convey, providing critical operational safety details.

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 well-structured with a numbered flow, an example command, and warnings, all in a dense but organized format. Every sentence adds necessary information, from step orchestration to safety caveats.

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?

The description comprehensively covers the multi-step nature, expected return values (key, uploadUrl, publicUrl), the external PUT requirement, expiration risk, and capability implications. No output schema exists, so the description fully compensates by explaining the return contract and sequence.

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 already covers all parameters with descriptions (100% coverage). The description adds useful context connecting parameters to the PUT request (e.g., using contentType in the curl header), emphasizing exact size, and showing how parameters fit into the step flow. This slightly exceeds the baseline for high schema coverage.

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 this is the first step of a media upload flow, returning a presigned URL for uploading raw bytes. It explicitly differentiates from upload_media (for tiny files) and finalize_media_upload, making the tool's purpose unmistakable.

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 provides explicit usage context: use for real image/video, not tiny files; gives the full 3-step flow; warns about URL expiration and recommends one file at a time. It also names the alternative upload_media and the dependent finalize_media_upload.

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