How to get build failure notifications in Replit

The first step is knowing where to look when a build fails. Open the Deployments pane from the left sidebar or by clicking the deploy/publish icon. Click the Logs tab to see real-time output from your deployment, including build step output, startup messages, and runtime errors. When a deployment fails, the Logs tab shows the exact error message and the build step that caused the failure. This is your manual monitoring baseline before setting up automated notifications.

Before building the notification script, you need a webhook URL that accepts incoming messages. For Slack, go to api.slack.com/apps, create a new app, enable Incoming Webhooks, and copy the webhook URL. For Discord, right-click a channel, select Edit Channel, go to Integrations, click Webhooks, create a new webhook, and copy the URL. The webhook URL is a secret — you will store it securely in the next step.

Open the Tools dock on the left sidebar and click Secrets (or search for 'Secrets' in the search bar). Add a new secret with the key SLACK_WEBHOOK_URL (or DISCORD_WEBHOOK_URL) and paste your webhook URL as the value. Secrets are encrypted with AES-256 and are available to your code via process.env. Never hardcode webhook URLs in your source code.

Create a file called notify.js in your project root. This script sends a formatted message to Slack or Discord when called. You will wire this into your build pipeline so it triggers only when a build step fails. The script reads the webhook URL from Secrets and sends a POST request with the error details. For Discord, the payload format uses 'content' instead of 'text'.

1// notify.js — sends build failure alerts to Slack or Discord
2const SLACK_URL = process.env.SLACK_WEBHOOK_URL;
3const DISCORD_URL = process.env.DISCORD_WEBHOOK_URL;
4
5async function sendAlert(message) {
6  const url = SLACK_URL || DISCORD_URL;
7  if (!url) {
8    console.error('No webhook URL configured in Secrets');
9    return;
10  }
11
12  const isDiscord = url.includes('discord.com');
13  const payload = isDiscord
14    ? { content: message }
15    : { text: message };
16
17  try {
18    const res = await fetch(url, {
19      method: 'POST',
20      headers: { 'Content-Type': 'application/json' },
21      body: JSON.stringify(payload),
22    });
23    if (!res.ok) console.error('Webhook failed:', res.status);
24  } catch (err) {
25    console.error('Failed to send alert:', err.message);
26  }
27}
28
29const errorMessage = process.argv[2] || 'Build failed — check deployment logs';
30const appName = process.env.REPL_SLUG || 'Unknown App';
31sendAlert(`Build failure in ${appName}: ${errorMessage}`);

Update your build script in package.json to call the notification script when any step fails. The || operator (OR) runs the next command only if the previous one fails — the opposite of && (AND). This way, the notification fires only on failure, not on success. The build still exits with a non-zero code so the deployment is properly aborted.

1{
2  "scripts": {
3    "build": "npm run compile && npm run test",
4    "compile": "tsc || (node notify.js 'TypeScript compilation failed' && exit 1)",
5    "test": "jest || (node notify.js 'Tests failed' && exit 1)",
6    "start": "node dist/index.js"
7  }
8}

For ongoing monitoring of your deployed app, create a separate Repl that pings your app's health endpoint on a schedule and sends an alert if the app is down. Use Replit's Scheduled Deployment feature to run this monitor every few minutes. Create a new Repl, add the health check script below, and deploy it as a Scheduled Deployment with a schedule like 'Every 5 minutes'. Store both the app URL and webhook URL in the new Repl's Secrets.

1// health-check.js — monitors your deployed app
2const APP_URL = process.env.APP_URL;
3const SLACK_URL = process.env.SLACK_WEBHOOK_URL;
4
5async function checkHealth() {
6  try {
7    const res = await fetch(`${APP_URL}/health`, {
8      signal: AbortSignal.timeout(5000),
9    });
10    if (!res.ok) {
11      await notify(`App returned ${res.status} — may be down`);
12    } else {
13      console.log('Health check passed');
14    }
15  } catch (err) {
16    await notify(`App unreachable: ${err.message}`);
17  }
18}
19
20async function notify(message) {
21  if (!SLACK_URL) return;
22  await fetch(SLACK_URL, {
23    method: 'POST',
24    headers: { 'Content-Type': 'application/json' },
25    body: JSON.stringify({ text: `Health Alert: ${message}` }),
26  });
27}
28
29checkHealth();