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Start by recording the request’s HTTP status, response body, and content type before changing WordPress settings. A JSON error usually points to the REST API route or its permissions; a 404 may be a permalink or rewrite issue, while an HTML response or blocked request can indicate a server, firewall, cache, or other intermediary. Work through the failing layer rather than disabling the REST API.
Start with the request and its response
Use the site’s actual hostname, exact REST route, and intended HTTP method. Then record the status code, response body, content type, and relevant request headers. WordPress REST API requests and responses use JSON, and the API uses HTTP status codes to communicate errors. The REST API reference explains the response format and error behavior.
- A JSON response containing a
rest_*error generally means the request reached the WordPress API layer. Read the message and code before changing configuration. - HTML instead of JSON, a blank response, or a server-generated error page warrants checks of the endpoint URL, redirects, rewrites, server, and intermediaries such as a firewall or CDN.
- Compare the response with a simple public core endpoint, if one is appropriate for the site. A difference can help distinguish a general routing or blocking issue from a particular route’s behavior.
Fix a 404 from /wp-json/
If the REST API root returns 404, first confirm that the hostname is correct and that the request is reaching the intended WordPress installation. Then check permalink routing. WordPress documents enabling pretty permalinks or using the rest_route query parameter as ways to investigate a /wp-json/ 404 in its Key Concepts guide.
- In the WordPress dashboard, open Settings → Permalinks and inspect the current permalink setting. If the site is configured to use plain permalinks, try a pretty-permalink option appropriate for the site.
- As a diagnostic, try the REST route through the query parameter form:
https://example.com/?rest_route=/. Replace the hostname with the site’s real address. If this works while/wp-json/does not, the difference points toward rewrite or permalink routing. - Check the web server’s rewrite rules and verify that query arguments are forwarded to WordPress. For Nginx, the handbook’s FAQ includes an example using
$is_args$argsin thetry_filestarget so query arguments are preserved.
Do not treat a 404 from one endpoint as proof the entire API is unavailable. If the root works but a specific route does not, check that route’s spelling, namespace and version, HTTP method, and whether the plugin or theme that registers it is active. The message “No route was found matching the URL and request method” means the requested path and method did not match an available route; it is different from a general connection failure.
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Resolve 401 and 403 authentication or permission errors
For a 401, a JSON rest_forbidden response, or a 403, establish how the request is being made: anonymously, from a logged-in session on the same site, or by a remote client. WordPress authentication behavior depends on that context; consult the official Authentication guide.
Logged-in requests from the same site
Cookie authentication is used for logged-in WordPress activity. For a manually constructed same-site request, include a valid REST nonce, commonly in the X-WP-Nonce header. Without the wp_rest nonce, WordPress treats the request as unauthenticated. Also check that the logged-in user has the capability required by the route’s action; a valid login alone does not grant every permission.
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Requests from an external client
Check that the client is using an authentication method configured for the site and that the request sends the expected credentials. WordPress recommends Application Passwords over its Basic Authentication plugin; the handbook describes that plugin as intended for development and testing.
Separate authentication from authorization
Authentication establishes who the request represents; authorization checks whether that user may perform the requested action. Inspect the route’s permission requirements and, for custom endpoints, its permission callback. A request can identify a user correctly and still fail because that user lacks the required capability.
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Investigate HTML responses, blocked requests, and server errors
A REST endpoint returning HTML, an unexpected status, or no usable response may be handled or changed before WordPress produces its normal JSON response. Check the endpoint URL and redirects, then review server and firewall logs alongside security, caching, CDN, theme, and plugin behavior.
- If a server-level 403 or HTML challenge appears, look for a firewall, security rule, CDN setting, or other intermediary blocking the request.
- If a route returns 400, validate its parameters and request payload. A WordPress.org support report describes a plugin or configuration conflict as one possible avenue, but an individual report does not establish a general cause.
- If the status is 500, inspect server logs and the route’s plugin or theme callback. One support report describes a plugin returning a
WP_Errorwithout status data and producing a 500; that is a reported implementation case, not a universal explanation. - If the request fails only on one route, compare that route with a simple public core endpoint and inspect the plugin or theme that supplies it.
When testing for a conflict, isolate likely plugins, theme behavior, or server rules in a controlled maintenance context. Change one variable at a time and restore normal operation after each test. WordPress.org support threads document possible failure patterns involving plugins, rewrite configuration, firewalls, and permission callbacks, but they are anecdotal and environment-specific: 404 report, 400 report, connection report, and 500 report.
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Use a low-risk troubleshooting order
- Observe: Capture the URL, method, status, response body, content type, and relevant headers.
- Classify: Decide whether the evidence points to route matching, authentication or capability checks, or server/intermediary behavior.
- Test the narrowest explanation: For a root 404, compare pretty-permalink routing with
?rest_route=/. For a 401/403, verify request context, nonce or credentials, and capability. For HTML or a server challenge, inspect logs and intermediary rules. - Change one thing at a time: Avoid broad security changes while the failing layer is still unclear.
- Escalate with evidence: If server-level behavior persists, share the captured request details and relevant logs with the hosting or server administrator.
Do not disable the REST API as a routine fix
WordPress warns that disabling the REST API can break administrative functionality that depends on it. Keep security changes targeted: identify the specific route or request being blocked and adjust only the relevant rule. WordPress also uses nonces for CSRF protection, and tightening CORS can prevent some authentication methods. Its REST API FAQ discusses these security and authentication considerations.
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