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Square Webhooks

How to Test Square Webhooks Locally (2026)

Square sends webhooks for payment, refund, order, invoice, and customer events. Square signs every webhook with HMAC-SHA256, computed over your notification URL concatenated with the raw request body using your webhook signature key.

With HookSense, point Square at a callback endpoint and let an AI agent await the result over MCP: create_callback_endpoint → wait_for_callback → verify_signature. Run npx @hooksense/mcp in Claude Desktop, Cursor, or any MCP client. No polling.

Signature Header

x-square-hmacsha256-signature

Algorithm

HMAC-SHA256 (over notification URL + raw body)

Setup Guide

  1. 1Create a free HookSense endpoint at hooksense.com
  2. 2Copy your unique webhook URL
  3. 3In the Square Developer Dashboard → your app → Webhooks → Subscriptions → Add Endpoint
  4. 4Paste your HookSense URL and choose the event types you need
  5. 5Copy the signature key and add it to HookSense for verification
  6. 6Send a test event from the dashboard or run a sandbox transaction
  7. 7Watch the webhook appear in HookSense in real-time

Common Square Webhook Events

payment.created
payment.updated
refund.created
refund.updated
order.created
order.updated
invoice.payment_made
customer.created

Forward to Localhost

Use HookSense CLI to forward Square webhooks directly to your local development server:

npx hooksense listen -p 3000 --path /api/integrations/square

No ngrok or tunnel setup required. Install with npm i -g hooksense or use npx.

Tips & Best Practices

  • Square's signature is computed over the notification URL + raw body — the exact endpoint URL matters
  • Use a constant-time comparison when verifying signatures to avoid timing attacks
  • Sandbox and production use separate signature keys — keep them straight in HookSense
  • Replay captured events to retest your handler without re-running a sandbox payment

Related

Square Webhook Documentation Square webhook tester — send sample events HMAC signature calculator
Webhook SignatureRaw Body2xx ResponseIdempotency

Give your agent a Square callback

Create a free callback endpoint and have an agent await its first verified Square webhook over MCP. Paid plans are early-access.

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