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S3 Uploader MCP Server

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S3 Uploader MCP Server

A Model Context Protocol (MCP) server that provides file upload functionality to AWS S3 buckets with automatic MIME type detection.

Features

  • Upload files to S3 buckets

  • Automatic MIME type detection based on file extensions

  • Support for common file types (images, documents, audio, video, archives)

  • Configurable S3 object keys

  • Comprehensive error handling

Related MCP server: MCP S3 File Uploader

Setup

Prerequisites

  • Node.js (version 14 or higher)

  • AWS credentials with S3 access

  • An S3 bucket

Installation

  1. Clone or download this repository

  2. Install dependencies:

    npm install

Configuration

Set the following environment variables:

export AWS_ACCESS_KEY_ID="your-access-key-id"
export AWS_SECRET_ACCESS_KEY="your-secret-access-key"
export AWS_REGION="your-aws-region"
export BUCKET_NAME="your-s3-bucket-name"

Usage

As an MCP Server

Start the server:

node index.js

The server exposes one tool:

upload_files

Upload a file to the configured S3 bucket.

Annotations:

  • Title: "Upload File to S3"

  • Read-only: false (modifies environment by uploading files)

  • Destructive: false (additive operation, doesn't remove existing data)

  • Idempotent: false (uploading same file again may overwrite or create new version)

  • Open-world: true (interacts with external AWS S3 service)

Parameters:

  • filePath (required): Absolute path to the file to upload

  • key (optional): S3 object key. If not provided, uses the filename

Example:

{
  "name": "upload_files",
  "arguments": {
    "filePath": "/path/to/your/file.jpg",
    "key": "uploads/my-image.jpg"
  }
}

Supported MIME Types

The server automatically detects MIME types for the following file extensions:

  • Images: jpg, jpeg, png, gif, webp, bmp, ico, svg, tiff

  • Documents: pdf, doc, docx, xls, xlsx, ppt, pptx, rtf

  • Text: txt, csv, html, css, js, json, xml, md

  • Audio: mp3, wav, ogg, m4a, flac

  • Video: mp4, avi, mov, wmv, flv, webm, mkv

  • Archives: zip, rar, tar, gz, 7z

  • Other: bin, exe, dmg (treated as binary)

Unknown file types default to application/octet-stream.

Integration with Claude Desktop

To use this MCP server with Claude Desktop, add it to your claude_desktop_config.json:

{
  "mcpServers": {
    "s3-uploader": {
      "command": "node",
      "args": ["/path/to/s3-mcp-server/index.js"],
      "env": {
        "AWS_ACCESS_KEY_ID": "your-access-key-id",
        "AWS_SECRET_ACCESS_KEY": "your-secret-access-key",
        "AWS_REGION": "your-aws-region",
        "BUCKET_NAME": "your-s3-bucket-name"
      }
    }
  }
}

Error Handling

The server provides detailed error messages for common issues:

  • Missing environment variables

  • File not found

  • Invalid file paths

  • AWS/S3 errors

  • Network connectivity issues

Security Considerations

  • Store AWS credentials securely (use environment variables, not hardcoded values)

  • Ensure the S3 bucket has appropriate permissions

  • Consider using IAM roles instead of access keys in production

  • Validate file types and sizes before upload if needed

Development

To test the server locally:

# Test tools listing
echo '{"jsonrpc": "2.0", "id": 1, "method": "tools/list"}' | node index.js

# Test file upload (replace with actual file path)
echo '{"jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": {"name": "upload_files", "arguments": {"filePath": "/path/to/test/file.txt"}}}' | node index.js

Available Tools

1 tool
upload_fileA

Upload a file to S3 bucket. The file will be uploaded with automatic MIME type detection based on file extension. Requires AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION, and BUCKET_NAME environment variables to be set.

ParametersJSON Schema
NameRequiredDescriptionDefault
keyNoOptional S3 object key. If not provided, will use the filename
filePathYesAbsolute path to the file to upload

TDQS

A3.8/5.0
Behavior3/5

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

Without annotations, the description discloses automatic MIME type detection and environment variable requirements. However, it does not cover other important behavioral aspects such as whether existing objects are overwritten or what error behavior might be expected.

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?

Two clear, front-loaded sentences with no redundant information. Every sentence contributes meaningful content.

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?

Adequate for a simple upload tool, covering the main action, prerequisites, and a behavioral detail. Could be improved with mention of return values or error handling, but the absence of an output schema makes the current level acceptable.

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?

The schema already covers both parameters with descriptions. The description adds no additional parameter semantics beyond what the schema provides, making the baseline score appropriate.

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

Purpose5/5

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

Clearly states it uploads a file to an S3 bucket with a specific verb and resource. No ambiguity about the action.

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

Usage Guidelines3/5

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

Provides prerequisite context (required environment variables) but does not discuss when to use this tool versus alternatives or any exclusions. Since there are no sibling tools, the lack of alternatives is understandable but not fully addressed.

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

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 1 tool updatev1.0.0
    • First observedupload_file
Deploy Server
One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

TDQS

A4/5.0

Scored across 1 tool

Disambiguation5/5

With only one tool, there is no possibility of confusion. The upload_file tool clearly defines its purpose and input.

Naming Consistency5/5

The single tool name 'upload_file' follows a clear verb_noun pattern, consistent with common conventions.

Tool Count3/5

The server provides only one tool, which is borderline thin but appropriate for a narrowly-scoped uploader service.

Completeness5/5

For an S3 uploader, the upload_file tool covers the essential operation thoroughly, with no obvious missing functionality within the stated scope.

Maintenance

ActivitySlowing
ResponsivenessNo issues

Resources

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