s3_create_multipart_upload

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

Annotations already convey non-read-only and non-idempotent behavior. The description adds useful operational context by clarifying that this call only initiates the upload, returns an UploadId, and does not upload data itself. However, it omits the important lifecycle fact that the initiated upload persists as unfinished state until completed or aborted, so it adds some but not rich behavioral disclosure.

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 carry purpose, scope, return value, and companion-tool routing without any filler. The key information is front-loaded in the first sentence.

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?

Combined with the schema, the description is sufficient for the immediate call: it implies required bucket/key, optional metadata, and the meaning of the returned UploadId. The main gap is lifecycle guidance—an initiated multipart upload should eventually be completed or aborted—and there is no output schema to fill that in, making the overall description informative but not fully complete.

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 about 83%, and the schema already explains bucket, key, metadata, contentType, and serverSideEncryption. The tool description adds no parameter-specific meaning beyond 'large file' and the returned UploadId, so it stays at the schema-coverage baseline of 3.

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 starts with a specific action ('Initiate an S3-compatible multipart upload') on a clear resource ('a large file in B2') and immediately names the companion sibling tool, s3_presign_upload_part, distinguishing this initiation step from per-part URL minting. There is no ambiguity about what the tool does.

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 clear usage context: use this when the file is large and when a multipart strategy is intended, and pass the returned UploadId to s3_presign_upload_part. However, it does not explicitly say when not to use it, such as recommending s3_put_object for small objects, or mention that completion/abort steps must follow.

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