mercury-invoicing-mcp

Mercury Banking MCP server with full Invoicing API support — first MCP to expose Mercury's accounts receivable endpoints.

A Model Context Protocol (MCP) server giving AI assistants (Claude, Cursor, Continue, etc.) full programmatic access to your Mercury business banking account, including the Invoicing API (one-shot + recurring) which is missing from every other Mercury MCP.

Why this MCP?

| Capability | Official Mercury MCP | dragonkhoi/mercury-mcp | mercury-invoicing-mcp | |---|:---:|:---:|:---:| | Banking read (accounts, transactions, statements) | ✅ | ✅ | ✅ | | Banking write (send_money, recipients) | ❌ | ✅ | ✅ | | Internal transfers between your own Mercury accounts | ❌ | ❌ | ✅ | | Invoicing API (create, update, cancel, attachments) | ❌ | ❌ | ✅ | | Customers AR + recurring invoices | ❌ | ❌ | ✅ | | Webhooks full CRUD (incl. update_webhook) | ❌ | ❌ | ✅ | | Built-in safeguards (rate limit, dry-run, redacted audit log) | ❌ | ❌ | ✅ | | Hosted (no token to manage) | ✅ | ❌ | ❌ | | Open source (MIT) | ❌ | ✅ | ✅ | | Total tools exposed | ~10 | ~11 | 34 |

For pure read-only consultation, prefer the official Mercury MCP. Use this one when you need to automate invoicing, write to Mercury, or expose Mercury to LLM agents safely.

Installation

npm install -g mercury-invoicing-mcp

Or use directly with npx:

npx mercury-invoicing-mcp

Configuration

The server reads MERCURY_API_KEY from the environment. Get your API key at Mercury Settings → API Tokens.

Recommended: use a token with the minimal scope needed. For invoicing-only usage, a token scoped to AR write is sufficient.

Sandbox mode

To test against Mercury's sandbox environment (no real money, pre-populated dummy data), just use a sandbox token:

MERCURY_API_KEY=secret-token:mercury_sandbox_xxxxxxxxxxxxxxxx

The MCP auto-detects sandbox tokens (those starting with mercury_sandbox_) and points to https://api-sandbox.mercury.com/api/v1 automatically.

To override the base URL explicitly (e.g. for a self-hosted proxy):

MERCURY_API_BASE_URL=https://your-proxy.example.com/api/v1

Claude Desktop / Claude Code

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (or ~/.claude.json for Claude Code):

{
  "mcpServers": {
    "mercury-invoicing": {
      "command": "npx",
      "args": ["-y", "mercury-invoicing-mcp"],
      "env": {
        "MERCURY_API_KEY": "secret-token:mercury_production_xxxxxxxxxxxxxxxx"
      }
    }
  }
}

Cursor

Add to ~/.cursor/mcp.json:

{
  "mcpServers": {
    "mercury-invoicing": {
      "command": "npx",
      "args": ["-y", "mercury-invoicing-mcp"],
      "env": {
        "MERCURY_API_KEY": "secret-token:..."
      }
    }
  }
}

OpenClaw

OpenClaw is an open-source self-hosted agent platform that supports MCP via @modelcontextprotocol/sdk. Add to ~/.openclaw/openclaw.json:

{
  "mcpServers": {
    "mercury-invoicing": {
      "command": "npx",
      "args": ["-y", "mercury-invoicing-mcp"],
      "env": {
        "MERCURY_API_KEY": "secret-token:..."
      }
    }
  }
}

Restart the gateway (docker restart openclaw-openclaw-gateway-1 or your equivalent). All tools become available to all your OpenClaw agents.

Tip: Use a Mercury read-only token if you want to expose the MCP to chat-channel agents (WhatsApp, Telegram, Slack). Mercury rejects any write operation regardless of which tool the LLM tries to call — defense in depth against prompt injection.

Tools (34 total)

Banking — Accounts

mercury_list_accounts, mercury_get_account
mercury_list_cards
mercury_get_organization
mercury_list_categories

Banking — Transactions

mercury_list_transactions, mercury_get_transaction
mercury_update_transaction (note, category)
mercury_send_money, mercury_request_send_money
mercury_create_internal_transfer (between your own Mercury accounts)

Banking — Recipients

mercury_list_recipients, mercury_add_recipient, mercury_update_recipient

Banking — Statements

mercury_list_statements

Treasury

mercury_get_treasury
mercury_list_treasury_transactions
mercury_list_treasury_statements

Invoicing (Accounts Receivable)

⚠️ Mercury Plus plan required. The Invoicing & Customers (AR) APIs are only available on Mercury's Plus plan (or higher). Calls to these tools return 403 Forbidden on Free or Standard plans. The other tools (banking, treasury, webhooks) work on every plan.

mercury_list_invoices, mercury_get_invoice
mercury_create_invoice, mercury_update_invoice
mercury_cancel_invoice
mercury_list_invoice_attachments

Customers (AR) — also requires Mercury Plus

mercury_list_customers, mercury_get_customer
mercury_create_customer, mercury_update_customer, mercury_delete_customer

Webhooks

mercury_list_webhooks, mercury_get_webhook
mercury_create_webhook, mercury_update_webhook, mercury_delete_webhook

Endpoints not yet wrapped — Mercury exposes ~25 additional endpoints that this MCP does not yet cover. They will land in upcoming releases. Tracked: PDF download (getinvoicepdf, getstatementpdf), attachments (uploadtransactionattachment, uploadrecipientattachment, getattachment, listrecipientsattachments), webhook signature verification (verifywebhook), webhook events (getevent, getevents), send-money approvals (listsendmoneyapprovalrequests, getsendmoneyapprovalrequest), credit lines (listcredit), users (getuser, getusers), Mercury Raise SAFE (getsaferequest(s), getsaferequestdocument), and OAuth flow (obtainaccesstoken, startoauth2flow).

Mercury does not expose list_send_money_requests, COA Templates or Journal Entries via the public API at all — those features are dashboard-only.

There is no send_invoice endpoint anywhere (API or dashboard). An invoice email is only sent when the invoice is created with sendEmailOption: "SendNow". To send a copy later, download the invoice PDF (Mercury UI button "Download PDF", or the getinvoicepdf endpoint — not yet wrapped, see "Endpoints not yet wrapped" above) and email it manually.

Tools available depend on your Mercury API token scope. The server registers all 34 tools but Mercury will reject unauthorized operations at the API level.

Security

Never share your API key. Use environment variables, never CLI args.
Use read-only or scoped tokens when you don't need write access.
Be aware of prompt injection risks when exposing write tools to LLMs that read untrusted content. See Anthropic's MCP security guidance.

Built-in safeguards

This MCP includes three middleware layers that activate automatically on write tools (read tools are unaffected):

1. Rate limiting

Per-category daily limits prevent runaway agents from draining accounts or spamming the API.

| Category | Tools | Default | |---|---|---| | money | send_money, request_send_money | 50/day | | internal_transfer | create_internal_transfer (between your own Mercury accounts) | 5/day | | invoicing | create/update/cancel invoice + create/update/delete customer | 100/day | | banking | add_recipient, update_recipient, update_transaction | 200/day | | webhooks | create/update/delete webhook | 5/day |

Override per category (units: /hour, /day, /week):

MERCURY_MCP_RATE_LIMIT_money=200/day      # bigger supplier batch
MERCURY_MCP_RATE_LIMIT_invoicing=1000/day # large monthly billing run
MERCURY_MCP_RATE_LIMIT_DISABLE=true       # disable all rate limiting (not recommended)

When exceeded, the tool returns an isError: true response with a clear message and retry hint — the agent learns to back off naturally.

2. Dry-run mode

Inspect what an agent would do without actually calling Mercury. Useful for debugging suspected behaviour or staging:

MERCURY_MCP_DRY_RUN=true

Write tools then return a structured payload describing the intended action without hitting the Mercury API.

3. Audit log (opt-in)

Enable structured JSON logging of every write call:

MERCURY_MCP_AUDIT_LOG=/var/log/mercury-mcp-audit.log

Each line is {ts, tool, result, args} (one JSON object per line). Result is ok, dry-run, or error. The path must be absolute; sensitive fields in args (accountNumber, routingNumber, apiKey, authorization, password, token, secret, ssn) are automatically redacted. The file is created with mode 0600 (owner read/write only).

Development

git clone https://github.com/klodr/mercury-invoicing-mcp.git
cd mercury-invoicing-mcp
npm install
npm run build
npm test

Inspiration

@stripe/mcp — architecture patterns
dragonkhoi/mercury-mcp — initial banking tool implementations
Official Mercury MCP — read-only reference

License

MIT — see LICENSE.

Contributing

Issues and PRs welcome. Please open an issue first for substantial changes.

Before submitting a PR:

npm install then npm test (must stay at 82/82 with ≥98% statement coverage)
npm run build (must succeed; the published tarball is only dist/index.js + package.json + README.md + LICENSE)
Update CHANGELOG.md under [Unreleased]
If you add or rename a tool, update the Tools section in this README and the defineTool(server, ...) call in src/tools/
New write tools must be registered in TOOL_CATEGORIES (src/middleware.ts) so they are rate-limited

For releases, do not edit version by hand — run npm version patch|minor|major; the lifecycle hook calls scripts/sync-version.mjs to propagate the bump into server.json and src/server.ts.

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