s3_upload_part_copy

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

Annotations already indicate readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the safety profile is established. The description adds contextual detail about assembling large objects without re-uploading, but does not disclose additional behavioral specifics such as failure modes, authentication requirements, or source-destination constraints. It neither contradicts nor substantially enriches the annotations.

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 with no filler. The action is front-loaded and the use-case rationale follows immediately. Every word earns its place.

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 and schema together are sufficient for invoking the tool, but since there is no output schema, the description does not explain what the response contains (e.g., the part ETag needed to complete the multipart upload). It also does not explicitly sequence the upload workflow, though uploadId referencing s3_create_multipart_upload implies it.

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 100%, so every parameter already has meaningful documentation. The tool description itself adds no parameter-level semantics beyond the schema, which puts this at the 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 names a specific verb ('Copy') and resource ('a part from an existing B2 object into an in-progress S3-compatible multipart upload'). This clearly distinguishes it from related siblings like s3_copy_object (whole object copy) and s3_put_object (new data upload).

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 second sentence tells the user when to use this tool: to efficiently assemble large objects from existing parts without re-uploading data. It provides clear context for the multipart upload workflow, though it does not explicitly name alternative tools or state when not to use it.

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