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Slack Webhooks

How to Test Slack Webhooks Locally (2026)

Slack sends webhooks for interactive components, slash commands, and Events API subscriptions. Slack uses a signing secret with HMAC-SHA256 to verify webhook authenticity.

Signature Header

X-Slack-Signature

Algorithm

HMAC-SHA256

Setup Guide

  1. 1Create a free HookSense endpoint at hooksense.com
  2. 2Copy your unique webhook URL
  3. 3In Slack App settings → Event Subscriptions → Enable Events
  4. 4Paste your HookSense URL as the Request URL
  5. 5HookSense automatically responds to Slack's URL verification challenge
  6. 6Subscribe to the events you need
  7. 7Mention your app or use a slash command to trigger a webhook

Common Slack Webhook Events

message
app_mention
channel_created
member_joined_channel
reaction_added
slash command
interactive message
view submission

Forward to Localhost

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

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

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

Tips & Best Practices

  • Slack requires a 200 response within 3 seconds — use HookSense custom responses to test timeout handling
  • The Events API sends a url_verification challenge on first setup
  • Use HookSense to debug interactive component payloads (buttons, modals, menus)
  • Slack's signing secret is different from your Bot Token — use the Signing Secret from App Credentials

Related

Slack Webhook Documentation HMAC Signature Calculator HMAC Verification Guide HookSense Documentation

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