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

With no annotations, the description carries the full burden and does disclose the non-obvious behavior that matters most: this is a two-phase protocol where the actual byte transfer happens outside the tool against a returned URL with exact headers. It omits other behavioral traits an agent would want — URL expiry, whether an uncompleted upload is retained or garbage-collected, and how sha256/size mismatch is handled.

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 sentences, zero filler, and the sequence is front-loaded so the agent learns the 'start' step before the follow-up instruction. Every clause carries actionable information.

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?

An output schema exists, so upload_url and headers needn't be described, and the input schema is well documented; the description fills the remaining gap by explaining the out-of-band PUT step and the handoff to complete_upload. Minor omissions around expiry and failure handling keep it from being fully self-sufficient for a multi-step tool.

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 83%, so the schema already documents file_name, content_type, sha256, and the image width/height requirements. The description adds no parameter-level meaning of its own and never references size_bytes or the relationship between the declared hash/size and the bytes actually PUT.

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?

States a specific verb and resource ('Start uploading one of the user's files') and explicitly frames it as the first half of a two-step flow by naming complete_upload, which separates it from that sibling. It stops short of saying what a 'reference' file is used for downstream, so the agent knows the mechanism but not the full intent.

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?

Gives a clear operational sequence: call this first, PUT the bytes to upload_url with exactly the returned headers, then call complete_upload. That is strong when-to-use guidance for the happy path, but it offers no exclusions or prerequisites — nothing about size limits, supported content types as a gate, or what to do if an upload is abandoned.

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