HTTP 500 Internal Server Error

Something went wrong on the server while processing your request. The server encountered an unexpected condition that prevented it from fulfilling the request. This is a generic server-side error that does not specify what went wrong.

What Is HTTP 500 Internal Server Error?

HTTP 500 Internal Server Error is a generic server-side error response indicating the server encountered an unexpected condition that prevented it from fulfilling the request. Unlike 4xx errors that indicate client mistakes, a 500 error is the server's fault. The client's request was valid, but something went wrong on the server during processing. The generic nature of 500 is intentional: it avoids leaking implementation details that could be exploited by attackers.

In production environments, 500 errors are one of the most critical issues a development team can face. They indicate unhandled exceptions, infrastructure failures, or bugs that escaped testing. Modern DevOps practices treat 500 errors as high-priority incidents that require immediate investigation. Tools like Sentry, Datadog, and New Relic automatically capture 500 errors with full stack traces, request context, and user information to accelerate debugging.

For API consumers, a 500 error means the request should be retried after a brief delay, since the server-side issue may be transient. However, if retrying consistently returns 500, the server has a persistent bug that the provider needs to fix. Unlike 4xx errors where the client must change its request, 500 errors require server-side intervention. Best practice is to implement retry logic with exponential backoff for 500 errors, combined with circuit breaker patterns that stop retrying after a threshold of failures.

Common Causes

Unhandled Exception

The application code threw an exception that was not caught by any error handler. This is the most common cause of 500 errors in web applications and APIs.

Database Connection Failure

The server cannot connect to the database due to incorrect credentials, connection pool exhaustion, network issues, or the database server being down.

Null Reference Error

The code attempted to access a property or method on a null or undefined value. This often happens when database queries return null for expected records or when optional data is not checked.

Configuration Error

Missing environment variables, incorrect file paths, invalid configuration values, or missing dependencies cause the request handler to fail during execution.

How to Fix

Check Server Logs

The 500 response typically does not include details for security reasons. Check your server logs, error tracking service, or application monitoring platform for the actual exception message and stack trace.

Add Global Error Handlers

Implement a global error handler in your web framework that catches unhandled exceptions, logs them with context, and returns a structured error response instead of exposing stack traces.

Verify Environment Configuration

Check that all required environment variables are set, database connection strings are correct, and external service credentials are valid. Missing configuration is a common cause of 500 errors in deployment.

Test Edge Cases

500 errors often result from untested edge cases like null values, empty arrays, missing optional fields, or unusually large inputs. Write tests that cover these scenarios.

Code Examples

Express.js

// Express.js — global error handling to prevent raw 500s
const express = require('express');
const app = express();

app.get('/api/users/:id', async (req, res, next) => {
  try {
    const user = await User.findById(req.params.id);
    if (!user) return res.status(404).json({ error: 'Not found' });
    res.json(user);
  } catch (err) {
    // Pass to global error handler
    next(err);
  }
});

// Global error handler — must have 4 parameters
app.use((err, req, res, next) => {
  // Log the full error for debugging
  console.error(`[ERROR] ${req.method} ${req.path}`, {
    message: err.message,
    stack: err.stack,
    timestamp: new Date().toISOString()
  });

  // Never expose stack traces in production
  const isDev = process.env.NODE_ENV === 'development';

  res.status(err.status || 500).json({
    error: 'Internal Server Error',
    message: isDev ? err.message : 'An unexpected error occurred',
    ...(isDev && { stack: err.stack }),
    requestId: req.headers['x-request-id'] || 'unknown'
  });
});

Flask (Python)

# Flask — global error handling to prevent raw 500s
from flask import Flask, jsonify, request
import logging
import traceback

app = Flask(__name__)
logger = logging.getLogger(__name__)

@app.route('/api/users/<int:user_id>', methods=['GET'])
def get_user(user_id):
    user = User.query.get(user_id)
    if user is None:
        return jsonify(error='Not found'), 404
    return jsonify(user.to_dict())

@app.errorhandler(500)
def internal_error(error):
    # Log the full error for debugging
    logger.error(
        f'500 error: {request.method} {request.path}',
        exc_info=True,
        extra={'request_id': request.headers.get('X-Request-Id', 'unknown')}
    )

    # Never expose stack traces in production
    if app.debug:
        return jsonify(
            error='Internal Server Error',
            message=str(error),
            traceback=traceback.format_exc()
        ), 500

    return jsonify(
        error='Internal Server Error',
        message='An unexpected error occurred',
        request_id=request.headers.get('X-Request-Id', 'unknown')
    ), 500

@app.errorhandler(Exception)
def handle_exception(e):
    logger.exception(f'Unhandled exception: {e}')
    return jsonify(error='Internal Server Error', message='Something went wrong'), 500

Frequently Asked Questions

What causes a 500 Internal Server Error?

The most common causes are unhandled exceptions in application code, database connection failures, null reference errors, missing configuration values, and resource exhaustion (memory or disk). The exact cause is in the server logs, not the error response.

Should I retry a 500 error?

Yes, 500 errors can be transient. Retry with exponential backoff, starting at 1 second and doubling each time. If the error persists after several retries, the server has a bug that needs to be fixed by the provider.

Why does the 500 response not include error details?

For security. Including stack traces, database details, or file paths in error responses could help attackers exploit vulnerabilities. Production servers should log the full error internally and return a generic message to clients.

What is the difference between 500 and 502?

HTTP 500 means the server itself encountered an error while processing the request. HTTP 502 Bad Gateway means the server is acting as a proxy or gateway and received an invalid response from the upstream server. Both are server-side errors but have different causes.

How do I prevent 500 errors?

Use try-catch blocks around database queries and external API calls, add global error handlers to your framework, validate all inputs before processing, write tests for edge cases, and monitor error rates with alerting tools.