Quick Diagnosis
Check the REST response status and body first. A 403, 404, and 500 point to different owners.
Problem
WordPress REST API Error
Diagnose WordPress REST API failures that break the block editor, Site Health, plugins, or app integrations by checking status codes, security rules, permalinks, and loopback behavior.
Problem
WordPress or a plugin cannot reach a REST endpoint successfully.
For: Site owners and support teams troubleshooting REST API warnings or editor failures.
Workflow
What to review
Editor Impact
The block editor depends on REST responses, so editor symptoms often reveal API problems.
WordPress AdminSeverity: MediumLast reviewed: 2026-09-16
Diagnosis
Symptoms, causes, checks, and fixes
Symptoms
- Block editor fails to load or save.
- Site Health reports a REST API error.
- Requests to /wp-json/ return 401, 403, 404, 500, redirects, or unexpected HTML.
Most Common Causes
- Security plugin blocking REST routes.
- Broken permalinks.
- Authentication or nonce failure.
- Server rewrite issues.
- Fatal error in a REST callback.
How To Confirm The Cause
- Open /wp-json/ in a private browser window.
- Check browser Network responses for REST requests.
- Temporarily review security/firewall rules that affect REST endpoints.
Fixes
- Flush permalinks from WordPress settings.
- Adjust firewall rules to allow legitimate REST routes.
- Fix the plugin or theme callback causing 500 errors.
How To Verify The Fix
- Confirm /wp-json/ returns JSON.
- Save a test post in the block editor.
- Re-run Site Health.
When To Contact Support
Escalate to hosting or a developer if server rewrites or PHP fatal errors cause REST failures.
References