helcim-mcp

Unofficial community MCP server and developer toolkit for the Helcim API. Secure, typed, agent-friendly, and read-only by default. Not affiliated with, sponsored by, maintained by, or endorsed by Helcim Inc.

helcim-mcp is a production-quality, TypeScript monorepo that makes it safe and easy for AI agents (and humans) to work with the Helcim payment platform. It ships three things:

1. @helcim-mcp/server - an MCP server exposing read-only Helcim tools (customers, invoices, card transactions, card batches, recurring payment plans, subscriptions, connection test).

2. @helcim-mcp/core - a typed, idempotency-aware Helcim API client with normalized errors, rate-limit handling, and secret redaction.

3. @helcim-mcp/webhooks - a standalone Helcim webhook verifier (HMAC-SHA256 signature verification, timestamp validation, replay protection, typed events).

Why would you use this?

• You want an AI agent to answer questions about your Helcim data - "what invoices are outstanding?", "show recent card transactions", "find the customer for this invoice", "which subscriptions need attention?" - without ever risking a financial mutation.

• You want a clean, typed Helcim client that handles the API's quirks (HTTP 200 ≠ success, errors object shapes, idempotency, rate limits, pagination) so you don't have to.

• You want to verify Helcim webhooks securely with constant-time signature comparison and replay protection, without re-inventing the HMAC scheme.

The MCP server is read-only by default. It physically cannot create, update, delete, or move money - there are no such tools. Even a token with full processing privileges cannot trigger a financial mutation through this server.

Quick start

1. Get a Helcim API token

Log in to your Helcim account (or a developer test account), go to All Tools → Integrations → API Access Configurations, and create a configuration. For read-only use, set General: Read, Settings: Read, and Transaction Processing: None.

2. Run the MCP server

# From source
git clone https://github.com/tejasghalsasi/helcim-mcp.git
cd helcim-mcp
pnpm install
pnpm rebuild esbuild   # required: pnpm 11 blocks esbuild's postinstall by default
pnpm build

# Set your token (never commit it)
export HELCIM_API_TOKEN="your_token_here"

# Run over stdio
node packages/mcp/dist/index.js

2b. Run with Docker (optional)

docker build -t helcim-mcp .
docker run --rm -e HELCIM_API_TOKEN=your_token_here helcim-mcp

2c. Run via npx (once published)

npx @helcim-mcp/server

3. Connect it to an MCP client

Add this to your MCP client config (e.g. Claude Desktop, Cursor, or any MCP client):

{
  "mcpServers": {
    "helcim": {
      "command": "node",
      "args": ["/absolute/path/to/helcim-mcp/packages/mcp/dist/index.js"],
      "env": {
        "HELCIM_API_TOKEN": "your_token_here"
      }
    }
  }
}

4. Ask your agent

Once connected, your agent can call tools like:

• connection_test - confirm the token works.

• list_invoices with status: "DUE" - "what invoices are outstanding?"

• list_card_transactions - "show recent card transactions."

• get_customer - "find the customer for this invoice."

• list_subscriptions with hasFailedPayments: true - "which subscriptions need attention?"

How read-only mode works

• The MCP server exposes only read tools. There are no payment, refund, capture, reversal, withdraw, settle, or delete tools.

• The core client exposes no write methods in v1.

• If a future version adds writes, it will require an explicit HELCIM_ENABLE_WRITES=true environment variable and a separate high-risk feature flag for financial mutations, with strong documentation and tests.

• HTTP 200 is not treated as success. Helcim explicitly warns that a 200 response does not mean the requested action succeeded; the client surfaces errors in the body as typed errors.

How credentials are protected

• The API token is read only from the HELCIM_API_TOKEN environment variable. Never hardcoded, never committed, never logged.

• All log lines and error messages pass through redact(). Token-like strings, card numbers, and F6L4 values are replaced with <redacted-...>.

• The token is never exposed to the model. The MCP server returns only redacted data and typed error codes.

• See SECURITY.md for the full security model.

Architecture

flowchart LR
    subgraph Client["MCP Client (LLM)"]
        A[Agent]
    end

    subgraph Server["@helcim-mcp/server"]
        M[MCP Server<br/>stdio transport]
        T[Read-only tools<br/>13 tools]
    end

    subgraph Core["@helcim-mcp/core"]
        C[HelcimClient]
        H[HelcimHttpClient<br/>auth, idempotency,<br/>rate-limit, redaction]
        E[Normalized errors]
    end

    subgraph Webhooks["@helcim-mcp/webhooks"]
        W[HelcimWebhookVerifier<br/>HMAC-SHA256, replay protection]
    end

    subgraph Helcim["Helcim API"]
        API[api.helcim.com/v2]
    end

    A -->|JSON-RPC over stdio| M
    M --> T
    T --> C
    C --> H
    H -->|HTTPS + api-token| API
    W -.->|verifies signed events| API

The monorepo layout:

helcim-mcp/
├── packages/
│   ├── core/       # Typed Helcim API client (read-safe)
│   ├── mcp/        # MCP server (read-only tools)
│   ├── webhooks/   # Webhook verifier
│   └── fixtures/   # Deterministic mock responses + test vectors
├── examples/       # Copy-paste usage examples
├── docs/           # Architecture, env reference, troubleshooting
└── scripts/        # Smoke test, CI helpers

Example interaction

Agent: "What invoices are currently outstanding?"

list_invoices(status: "DUE")
→ { count: 2, invoices: [
    { invoiceId: 28658838, invoiceNumber: "INV1000", status: "DUE", currency: "CAD", customerId: 2488717 },
    { invoiceId: 28658839, invoiceNumber: "INV1001", status: "DUE", currency: "USD", customerId: 2488718 }
  ] }

Agent: "Show recent card transactions."

list_card_transactions(limit: 5)
→ { count: 2, transactions: [
    { transactionId: 25557533, status: "APPROVED", type: "purchase", amount: 100.99, currency: "CAD", cardType: "MC", customerCode: "CST1000" },
    { transactionId: 25557534, status: "DECLINED", type: "purchase", amount: 250.00, currency: "CAD", cardType: "VI", customerCode: "CST1001" }
  ] }

Agent: "Find the customer associated with this invoice."

get_invoice(invoiceId: 28658838) → { customerId: 2488717, ... }
get_customer(customerId: 2488717) → { customerCode: "CST1000", businessName: "Acme Widgets Ltd", ... }

Agent: "Show subscriptions requiring attention."

list_subscriptions(hasFailedPayments: true)
→ { count: 1, subscriptions: [ { id: 42, status: "ACTIVE", hasFailedPayments: true, customerCode: "CST1000", ... } ] }

Agent: "Process a refund for transaction 25557533."

→ Error: Unknown tool: process_refund

The agent cannot move money. There is no such tool.

Webhook verification

import { HelcimWebhookVerifier } from '@helcim-mcp/webhooks';

const verifier = new HelcimWebhookVerifier(process.env.HELCIM_VERIFIER_TOKEN!);

// In your webhook handler (e.g. Next.js route handler):
export async function POST(req: Request) {
  const body = await req.text();
  const headers = Object.fromEntries(req.headers.entries());
  try {
    const verified = verifier.verify(headers, body);
    // verified.event.type === 'cardTransaction' | 'terminalCancel'
    return new Response('ok', { status: 200 });
  } catch (err) {
    return new Response('invalid signature', { status: 401 });
  }
}

See examples/webhook-nextjs.md for a full Next.js example.

Environment variables

See docs/environment.md for the full reference.

Reference

• Supported tools & API matrix - every MCP tool and core client method mapped to its Helcim endpoint.

• Architecture - design decisions and data flow.

• Troubleshooting - common issues and fixes.

• Environment reference - all env vars.

• Release process - how to cut a release.

Development

pnpm install
pnpm rebuild esbuild  # pnpm 11 blocks esbuild's postinstall by default
pnpm build        # build all packages
pnpm test         # run all tests
pnpm typecheck    # type-check all packages
pnpm lint         # prettier check
pnpm smoke        # verify the built server exposes only read-only tools

License

MIT. See LICENSE.

Disclaimer

This is an independent community project. It is not affiliated with, sponsored by, maintained by, or endorsed by Helcim Inc. "Helcim" is a trademark of Helcim Inc. and is used here only to describe API compatibility. This project does not use Helcim logos or branding.