s3-mcp

Put S3 object

s3_put_object

Destructive

Upload text or binary data to an S3-compatible bucket. Supports base64 encoding for binary payloads and requires write access to be enabled.

Instructions

Upload object content. Requires S3_ALLOW_WRITE=true. Pass encoding=base64 to upload binary data from a base64 string.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "bucket": "<bucket>",
      "key": "<key>",
      "content": "<content>"
    },
    "name": "s3_put_object"
  }
}

Input Schema

Name	Required	Description
`key`	Yes	Object key
`bucket`	Yes	Bucket name
`content`	Yes	Object body (text or base64)
`encoding`	No	How to decode content (default: utf8)
`metadata`	No	User metadata key/value map
`contentType`	No	Content-Type header

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Sep 13, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already declare destructiveHint=true and openWorldHint=true, so the mutation/global side effects are covered. The description adds value by disclosing the S3_ALLOW_WRITE=true authorization gate, which an agent cannot infer from annotations or schema. It omits whether existing keys are overwritten, which would be the remaining useful detail.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences with the core action first, then the prerequisite, then the binary-data hint. No filler and everything is front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with no output schema and full schema coverage, the definition covers the action, the authorization prerequisite, and binary encoding. The main gap is overwrite/conflict behavior on an existing key, which is relevant for a put operation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so bucket, key, content, encoding, metadata, and contentType are all documented in the schema. The description's encoding=base64 note merely restates the enum's intent, adding no syntax or edge-case detail beyond the structured fields, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Upload object content'), which is unambiguous against siblings like s3_read_object, s3_delete_object, and s3_list_objects. It does not explicitly name a sibling to disambiguate, but the write action is inherently distinct from the read/list/delete tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a concrete precondition ('Requires S3_ALLOW_WRITE=true') and a format hint ('Pass encoding=base64 to upload binary data'), which tells the agent when the tool will work and how to handle binary payloads. It stops short of comparing against alternatives or stating 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.

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