{
  "id": 9526082,
  "title": "Stop guessing why your webhook signature check fails",
  "url": "https://urgent.news/2026/09/24/stop-guessing-why-your-webhook-signature-check-fails",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-09-24T08:47:12.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/webhooker-eu/stop-guessing-why-your-webhook-signature-check-fails-17a0"
  },
  "original_language": "en",
  "account": "When a webhook signature check fails, it's crucial to understand the four possible reasons behind it: the signing secret, the exact request body bytes, the hash algorithm, and the result encoding. These reasons are the only four factors that can cause a mismatch between the computed HMAC and the one received.\n\nTo pinpoint the issue, begin by logging two key metrics: the length of the raw body and its SHA256 hash. This approach allows you to quickly determine whether the body was modified before hashing. If the byte count doesn't match the content-length header, the body has been altered, which is often the most common cause of the failure. Common culprits include JSON parsers or framework middleware that modify the body inadvertently.\n\nOnce you've confirmed the body is intact, focus on the HMAC computation. First, verify the encoding by comparing the computed hash against a known answer using the correct encoding - hex for Stripe and base64 for Shopify. A mismatch here could be due to a trailing newline or space in the secret, which often goes unnoticed in logs.\n\nNext, ensure you're using the correct signing secret. It should begin with \"whsec_\" for Stripe and match the values provided in the dashboard. Avoid using the API key, as it will not verify any signature.\n\nOn edge runtimes like Cloudflare Workers, Deno Deploy, and Vercel Edge, be aware that synchronous crypto functions can cause issues. Use the async variant instead, and remember that the request body can only be read once on these platforms. Read the text first and then parse it to avoid empty strings and incorrect hash calculations.\n\nLastly, if you're manually computing the HMAC on an edge runtime, use the Web Crypto API, which supports asynchronous operations. This will ensure compatibility with the edge environment and help resolve any signature verification errors.",
  "summary": "No signatures found matching the expected signature for payload . That is Stripe's wording. GitHub gives you a mismatch on X-Hub-Signature-256 , Shopify words it differently again, and hand written handlers usually log something like \"invalid signature\". They all mean exactly one thing: the HMAC you computed is not the HMAC that arrived. What none of them tell you is which input was wrong. And…",
  "key_points": [
    "Log raw body length and SHA256 hash to detect body modification",
    "Verify HMAC encoding (hex for Stripe, base64 for Shopify) and signing secret format"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}