s3-mcp

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put_object

Upload data to an S3 bucket by specifying bucket, key, and body. Set base64=true when the body contains binary or base64-encoded content.

Instructions

Write an object. Set base64=true when body is base64-encoded binary.

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>",
      "body": "<body>"
    },
    "name": "put_object"
  }
}

Input Schema

Name	Required	Description	Default
`key`	Yes
`body`	Yes
`base64`	No
`bucket`	Yes

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 18, 2026

TDQS

C2.7/5.0

Behavior2/5

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

With no annotations, the description carries the full burden of behavioral disclosure صح. It reveals the base64 flag semantics but does not mention overwrite behavior, idempotency, permissions, size limits, or what happens to existing objects with the same key.

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

Conciseness4/5

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

The description is brief and front-loaded, with the core action in the first sentence and a useful parameter caveat in the second. It avoids waste, though the first sentence is somewhat tautological with the tool name.

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

Completeness2/5

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

For a tool with no annotations wagering, a full schema coverage gap, and direct mutation side effects, the description is too sparse. It does not explain required parameters, overwrite semantics, or how this fits among sibling operations. An output schema exists but is not described, so return values remain unknown for safety-critical checks.

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

Parameters2/5

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

Schema description coverage is 0%, so the description must explain parameters. It clarifies the base64 boolean, but bucket, key, and body remain only title-level with no additional meaning. The description does not compensate for the missing schema descriptions across most parameters.

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?

The description states the action clearly with the verb 'Write' and the resource 'object', making the purpose immediately identifiable. It distinguishes from siblings like get_object and delete_object, though it does not explicitly contrast with presign_put beyond the implied direct write.

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

Usage Guidelines2/5

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

No guidance is given on when to use put_object versus alternatives such as presign_put or copy_object. The only usage hint is the base64 condition, which is a parameter detail rather than a selection criterion.

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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