> ## Documentation Index
> Fetch the complete documentation index at: https://checklyhq.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# API Check Troubleshooting

> Learn how to troubleshoot API checks with Checkly.

API checks can be tricky to troubleshoot. Here are some common issues and solutions:

## Getting the `Error: ESOCKETTIMEDOUT` error

Sometimes API checks return this error, without any other information on what caused it.

* This is a socket timeout error. Essentially there is no successful connection with the API at the TCP and/or DNS level.
  Then, Checkly is closing the connection after the usual 30 seconds timeout, because the server didn’t respond.
* Usually the root cause for this error is intermittent network issues on the application side.
* There will probably be no errors in the application logs, as it was not even possible to establish a connection.
* The response headers will be empty. If Checkly doesn't get a connection, there is nothing to send back, e.g. the response headers.

## Authentication Problems

**Issue: 401/403 status codes, authorization errors**

**Solutions**:

1. Verify API credentials are correct and active
2. Check token expiration and refresh if needed
3. Validate authentication headers format
4. Test API manually with same credentials

## Timeout Issues

**Issue: Requests timing out, slow responses**

**Solutions**:

1. Check API server performance and load
2. Verify network connectivity from monitoring locations
3. Increase timeout thresholds if appropriate
4. Investigate API infrastructure capacity

## Assertion Failures

**Issue: Unexpected response content or format**

**Solutions**:

1. Review actual API response vs. expected format
2. Update assertions for API changes
3. Check for environment-specific differences
4. Validate test data and dependencies