Direct answer: Keep four things close when a webhook misbehaves: the raw request body, the signature base string, a JSON formatter, and a way to replay a sanitized request. These basics diagnose more webhook failures than a large collection of SDK-specific helpers.
Webhook problems feel mysterious because the visible symptom is usually late and indirect. A billing platform says delivery failed. Your application says a signature is invalid. A customer says an update never arrived. The useful evidence is not the final error screen; it is the exact request that crossed the boundary between the sender and your endpoint.
Start by capturing the request safely. Save the timestamp, relevant headers, raw body, and response status, but redact authorization values and personal data before sharing it. Do not parse the body before you verify the signature if the provider signs raw bytes. A JSON parser can normalize whitespace or key order, which makes a later signature check fail even though the payload looks unchanged to a human.
Then separate transport from application behavior. Confirm that the sender reached the expected URL and that the endpoint returned a response quickly. A timeout, redirect, or wrong path is a delivery problem. A successful delivery followed by rejected content is a contract problem. This distinction prevents a lot of wasted time changing business logic while the endpoint address is wrong.
Format the JSON only after preserving the raw version. Look for the practical differences: an event type that changed, a nested field that became nullable, a number sent as a string, or a timestamp in seconds rather than milliseconds. A side-by-side diff is usually faster than reading two large payloads line by line.
Finally, replay the smallest sanitized request that reproduces the issue. If a replay succeeds while the original fails, compare headers and raw bytes. If both fail, reduce optional fields until the boundary that causes the rejection is obvious. Save the resulting request as a regression fixture so the next change produces an actionable test failure instead of another production surprise.
GetCodingTools covers this small stack in one browser workflow: inspect headers, format JSON, compare payloads, convert timestamps, validate URL encoding, and keep a safe replay preset for later verification.