s3-mcp

original work from https://github.com/aws-samples/sample-mcp-server-s3

s3-mcp is a Model Context Protocol (MCP) server for AWS S3 and S3-compatible object stores (for example MinIO, Cloudflare R2, and Backblaze B2 S3). It exposes buckets and objects through MCP resources and tools so LLM clients can browse and fetch content from object storage.

What this server exposes

Resources

• s3://<bucket>/<key> resources generated from discovered buckets and objects
• Up to 1,000 objects per bucket listing request
• Bucket listing is limited by S3_MAX_BUCKETS (default: 5)

Tools

• ListBuckets - list buckets accessible by configured credentials
• ListObjectsV2 - list objects in a bucket (supports prefix and max_keys)
• GetObject - fetch an object by bucket_name + key

Quick start

1. Sync dependencies:

uv sync --no-install-project

2. Create a local environment file from the template:

cp env.example .env

3. Set credentials and endpoint settings in .env.

4. Run the server:

PYTHONPATH=src .venv/bin/python -m s3_mcp_server.server

The server runs over stdio (as MCP servers normally do).

Configuration

You can configure this project with environment variables, an optional JSON/TOML config file, or the default AWS SDK credential chain.

Credential and setting precedence

1. Environment variables (S3_*, AWS_*)
2. S3_CONFIG_FILE + S3_CONFIG_PROFILE
3. Botocore/AWS SDK credential provider chain

Important environment variables

• S3_REGION / AWS_REGION - region used for request signing
• S3_ENDPOINT_URL - required for most non-AWS providers
• S3_ACCESS_KEY_ID, S3_SECRET_ACCESS_KEY, S3_SESSION_TOKEN
• S3_ADDRESSING_STYLE - auto, path, or virtual
• S3_SIGNATURE_VERSION - usually s3v4
• S3_VERIFY_SSL - set false only for local/self-signed development
• S3_MAX_BUCKETS - max buckets processed per list call

Bucket allow-list (recommended for restricted credentials)

You can bypass the ListBuckets permission requirement by explicitly declaring allowed buckets:

• S3_BUCKETS=my-bucket-a,my-bucket-b
• or indexed vars: S3_BUCKET_1, S3_BUCKET_2, ...
• or config file keys: buckets, bucket_names, or s3_buckets

Optional config file

Set:

• S3_CONFIG_FILE=/absolute/path/to/s3.config.toml (or .json)
• S3_CONFIG_PROFILE=default

See s3.config.example.toml for profile examples.

Claude Desktop example

Claude Desktop config path:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "s3-mcp-server": {
      "command": "/absolute/path/to/s3-mcp/.venv/bin/python",
      "args": ["-m", "s3_mcp_server.server"],
      "env": {
        "PYTHONPATH": "/absolute/path/to/s3-mcp/src",
        "S3_ENDPOINT_URL": "http://localhost:9000",
        "S3_REGION": "us-east-1",
        "S3_ACCESS_KEY_ID": "replace-me",
        "S3_SECRET_ACCESS_KEY": "replace-me",
        "S3_BUCKETS": "my-bucket"
      }
    }
  }
}

Debugging

The easiest way to inspect requests and responses is with the MCP Inspector:

npx @modelcontextprotocol/inspector /absolute/path/to/s3-mcp/.venv/bin/python -m s3_mcp_server.server

License

This project is licensed under MIT-0. See LICENSE.