Resend Blade MCP

Security-first MCP server for Resend transactional email — send, manage contacts, broadcasts, templates, domains, and webhooks with programmatic safety controls.

Built on FastMCP 2.0 and httpx. Designed for agentic workflows where LLMs operate autonomously.

Why not the official Resend MCP?

The official resend-mcp covers the full API but was designed for human-supervised chat, not autonomous agents. In agentic contexts, its security model breaks down:

Capability	resend-blade-mcp	Official resend-mcp	Generic vendor MCPs
Write gating	Programmatic env var gate	Prompt engineering only	Usually none
Filesystem access	None — base64/URL only	filePath reads any file	Varies
API key management	Excluded entirely	Full CRUD exposed to agent	Often exposed
Credential scrubbing	All error paths scrubbed	Not implemented	Rarely
Tool count	28 focused	60+ (context window bloat)	Varies
Output format	Pipe-delimited, null omission	Raw JSON responses	Raw JSON
HTTP transport auth	Built-in bearer middleware	Per-session key only	Rarely
Idempotency	Native Idempotency-Key header	Not exposed as parameter	Rarely
Rate limit handling	Typed RateLimitError with retry-after	Raw error passthrough	Varies

The filesystem problem

The official MCP accepts filePath in attachments, calling fs.readFile() with no path validation. An autonomous agent could read /etc/passwd, ~/.ssh/id_rsa, or any file on the host and attach it to an email sent to any address. resend-blade-mcp rejects all filesystem paths — only base64 content and HTTPS URLs are permitted.

The API key problem

The official MCP exposes create-api-key and remove-api-key tools. An agent could create a full-access API key and exfiltrate it, or delete existing keys to disrupt services. resend-blade-mcp excludes API key management entirely — these are privileged operations that belong out-of-band.

Features

• 28 tools across 8 categories: sending, contacts, segments, broadcasts, templates, domains, webhooks, logs
• Write-gate — all mutating operations disabled by default (RESEND_WRITE_ENABLED=true to enable)
• No filesystem access — attachments via base64 content or HTTPS URL only
• No API key CRUD — excluded by design, not just gated
• Credential scrubbing — re_* API keys stripped from all error output
• Token-efficient — pipe-delimited output, null-field omission, capped lists
• Idempotent sends — native Idempotency-Key support prevents duplicate emails on retry
• Webhook management — create, list, delete webhook endpoints for event-driven architectures
• Sidereal Marketplace — native plugin manifest for one-click install

Requirements

• macOS (tested) or Linux
• Python 3.12+
• uv
• Resend account with API key (get one here)

Quick Start

# Clone and install
git clone https://github.com/Groupthink-dev/resend-blade-mcp.git
cd resend-blade-mcp
uv sync

# Set your API key
export RESEND_API_KEY=re_xxxxxxxx

# Run (stdio transport)
uv run resend-blade-mcp

Claude Code

claude mcp add resend-blade -- uv run --directory ~/src/resend-blade-mcp resend-blade-mcp

Claude Desktop (claude_desktop_config.json)

{
  "mcpServers": {
    "resend-blade": {
      "command": "uv",
      "args": ["run", "--directory", "/path/to/resend-blade-mcp", "resend-blade-mcp"],
      "env": {
        "RESEND_API_KEY": "re_xxxxxxxx",
        "RESEND_WRITE_ENABLED": "false"
      }
    }
  }
}

Tools (28)

Sending (5)

Tool	Gate	Description
resend_send	write	Send email (HTML/text, attachments, scheduled, idempotent)
resend_send_batch	write	Batch send up to 100 emails
resend_get_email	read	Retrieve sent email by ID
resend_list_emails	read	List sent emails with status
resend_cancel_scheduled	write	Cancel a scheduled email

Contacts (4)

Tool	Gate	Description
resend_create_contact	write	Create a contact with properties
resend_list_contacts	read	List contacts
resend_update_contact	write	Update contact properties
resend_delete_contact	write	Delete a contact

Segments (3)

Tool	Gate	Description
resend_create_segment	write	Create a segment
resend_list_segments	read	List segments
resend_delete_segment	write	Delete a segment

Broadcasts (4)

Tool	Gate	Description
resend_create_broadcast	write	Create a broadcast (draft)
resend_send_broadcast	write	Send or schedule a draft broadcast
resend_list_broadcasts	read	List broadcasts with status
resend_delete_broadcast	write	Delete a draft/scheduled broadcast

Templates (4)

Tool	Gate	Description
resend_create_template	write	Create template with variables
resend_list_templates	read	List templates
resend_get_template	read	Get template with HTML content
resend_publish_template	write	Publish template for use in sends

Domains (4)

Tool	Gate	Description
resend_add_domain	write	Register a sending domain (returns DNS records)
resend_list_domains	read	List domains with verification status
resend_get_domain	read	Get domain with DNS record details
resend_verify_domain	write	Trigger DNS verification

Webhooks (3)

Tool	Gate	Description
resend_create_webhook	write	Create webhook endpoint (returns signing secret)
resend_list_webhooks	read	List webhook endpoints
resend_delete_webhook	write	Delete a webhook

Logs (1)

Tool	Gate	Description
resend_list_logs	read	List recent API request logs

Security

Layer	Control
API key	RESEND_API_KEY from env (never logged, scrubbed from errors)
Transport	stdio default (no network exposure)
Write gate	RESEND_WRITE_ENABLED default false — blocks all 17 write tools
Attachments	Base64 content or HTTPS URL only — filesystem paths rejected
API key CRUD	Excluded — no tool can create, list, or delete API keys
Batch limits	resend_send_batch capped at 100 (Resend API maximum)
Credential scrubbing	re_* patterns removed from all error output
HTTP auth	Optional bearer token middleware (RESEND_MCP_API_TOKEN)
Rate limits	429 responses surface as typed RateLimitError with retry-after

HTTP Transport

export RESEND_MCP_TRANSPORT=http
export RESEND_MCP_HOST=127.0.0.1
export RESEND_MCP_PORT=8770
export RESEND_MCP_API_TOKEN=your-secret-token

uv run resend-blade-mcp

Environment Variables

Variable	Default	Description
RESEND_API_KEY	(required)	Resend API key
RESEND_WRITE_ENABLED	false	Enable write operations
RESEND_MCP_TRANSPORT	stdio	Transport: stdio or http
RESEND_MCP_HOST	127.0.0.1	HTTP bind host
RESEND_MCP_PORT	8770	HTTP bind port
RESEND_MCP_API_TOKEN	(none)	Bearer token for HTTP auth

Development

make install-dev    # Install with dev dependencies
make test           # Run unit tests (mocked, no Resend needed)
make test-e2e       # Run E2E tests (requires live API key)
make check          # Lint + format + type-check
make run            # Start the server

License

MIT