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Reference

Complete technical reference for mcp-s3.

Section Description
Tools API All tool parameters, responses, and error codes
Configuration Environment variables and configuration options
Security Limits, authentication, and verification

Tools

Tool Description
s3_list_buckets List accessible S3 buckets
s3_list_objects List objects with prefix/delimiter/pagination
s3_get_object Retrieve object content
s3_get_object_metadata Get metadata without content (HEAD)
s3_put_object Upload object (blocked by default)
s3_delete_object Delete object (blocked by default)
s3_copy_object Copy object within/between buckets
s3_presign_url Generate presigned GET/PUT URLs
s3_list_connections List configured S3 connections

Environment Variables

Connection

Variable Default Description
AWS_REGION us-east-1 AWS region
AWS_ACCESS_KEY_ID Access key
AWS_SECRET_ACCESS_KEY Secret key
AWS_SESSION_TOKEN Session token (optional)
AWS_PROFILE Profile name (optional)
S3_ENDPOINT Custom endpoint for S3-compatible storage
S3_USE_PATH_STYLE false Use path-style URLs
S3_TIMEOUT 30s Operation timeout

Extensions

Variable Default Description
MCP_S3_EXT_READONLY true Block write operations
MCP_S3_EXT_SIZELIMIT true Enforce size limits
MCP_S3_MAX_GET_SIZE 10MB Max bytes for GET
MCP_S3_MAX_PUT_SIZE 100MB Max bytes for PUT
MCP_S3_EXT_LOGGING false Enable request logging
MCP_S3_EXT_AUDIT false Enable audit logging

Limits

Limit Default Maximum
GET size 10MB Configurable
PUT size 100MB Configurable
Operation timeout 30s 300s

Blocked Operations (Read-Only Mode)

  • s3_put_object
  • s3_delete_object

Release Verification

All releases include:

  • Checksums - SHA256 verification
  • SLSA Provenance - Level 3 build attestation
  • Cosign Signatures - Keyless verification
# Verify with Cosign
cosign verify-blob \
  --bundle mcp-s3_*.tar.gz.sigstore.json \
  mcp-s3_*.tar.gz