Write one chunk to an upload session

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

With no annotations, the description carries full burden and does add valuable behavior: it reveals that a wrong offset produces a repairable error with the correct cursor rather than failing the transfer. It also implies state mutation through 'append', though it does not detail broader side effects.

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 focused sentences deliver the core operation and a key failure-mode detail. Every sentence earns its place; no filler or redundant restating.

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?

For a 3-parameter no-annotation tool it covers the operation, the input encoding, and a non-obvious error behavior. It falters only on defining the session handle and how the cursor is obtained, which an agent would need to invoke correctly.

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 only 33%, and the description compensates somewhat by explaining offset semantics ('expected offset' and cursor recovery). However, the required 'handle' parameter is left unexplained, and 'data' only repeats what the schema already says.

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 ('Append') and resource ('base64 chunk at the session's expected offset'), making the operation unmistakable. It also distinguishes from sibling tools like file_transfer_open and file_transfer_commit by signaling this is the chunk-append step.

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 implies use during an ongoing upload session via 'session's expected offset', but it does not explicitly state when to use this tool vs file_transfer_open/file_transfer_commit, nor any prerequisites such as opening a session first.

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