Open a resumable file transfer

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

With no annotations, the description carries the burden, and it discloses a key behavioral trait: 'Sessions survive server restarts — resume at the reported nextOffset.' It also clarifies the upload/download protocol. It would be stronger with cleanup or session-identity details, but the disclosed persistence is genuinely useful.

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?

Three short sentences with no fluff; the most important scoping ('chunked upload or download session') is front-loaded, and the protocol details are organized by direction. Every sentence adds 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?

The lifecycle (open → write/read → commit/EOF) is described and persistence is noted, but there is no output schema and the description does not specify what open returns beyond a reported nextOffset—no session/handle identifier is mentioned. It also omits any cleanup/cancel path, so an agent may not have everything needed to invoke this correctly in all cases.

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 coverage is 75%, and the description compensates by mapping direction to concrete workflows: upload starts at offset 0 and ends with commit, download reads until eof. It also clarifies that resumption uses a reported nextOffset. Size and sha256 remain at schema level, but their schema descriptions are already adequate.

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 uses a specific verb ('Open') and names the resource: a chunked upload or download session. It differentiates itself from siblings by situating the tool at the start of a clear workflow: upload via file_transfer_write then file_transfer_commit, download via file_transfer_read until eof.

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?

It gives concrete usage context for both directions, explicitly naming sibling tools in sequence and telling the agent to start at offset 0 or read until eof. It does not explicitly state when not to use this tool or mention alternatives like file_transfer_status, so it falls short of a 5.

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