List the parts uploaded for an in-progress S3 multipart upload to check which parts exist and continue where you left off.
List the parts that have been uploaded for an in-progress S3-compatible multipart upload.
| Name | Required | Description | Default |
|---|---|---|---|
| key | Yes | The object key. | |
| bucket | Yes | The bucket name. | |
| maxParts | No | ||
| uploadId | Yes | The UploadId. | |
| partNumberMarker | No | Pagination cursor. |
Changes observed during successful MCP inspections.
v0.2.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, so the description does not need to restate safety. It adds the useful context that the upload must be in-progress, but it does not disclose pagination behavior, response shape, or any error conditions, so it stays at the baseline.
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?
A single, front-loaded sentence communicates the operation, resource, and required state with no redundant wording. Every word contributes to the agent's understanding.
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 simple read-only list operation, the description plus schema annotations cover the essential invocation details: the operation, the target resource, and the in-progress state. It does not describe the return object, but a list operation of this kind is still sufficiently callable without that detail.
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?
The schema covers 80% of parameters, documentating bucket, key, uploadId, and partNumberMarker, leaving only maxParts without a description. The description does not add meaning to any parameter beyond the schema, so the baseline of 3 is appropriate.
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 ('List'), a clear resource ('parts'), and a scoping condition ('an in-progress S3-compatible multipart upload'). This clearly distinguishes it from sibling tools like s3_list_multipart_uploads, which list uploads rather than parts, and from s3_upload_part_copy.
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 phrase 'in-progress' provides clear context that this tool is for active multipart uploads, implying it is not for completed uploads. It does not explicitly name alternatives or exclusions, but the intended use case is clear enough without additional guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.