Runtime Diagnostics

PHP 500 Error Debugging Guide

Trace PHP HTTP 500 responses through the reverse proxy, PHP-FPM pool, application logs, runtime configuration and failing request context. Last updated September 20, 2026.

Trace PHP HTTP 500 responses through the reverse proxy, PHP-FPM pool, application logs, runtime configuration and failing request context. This reference is written for developers who need practical validation behavior, reviewable rules and safe examples rather than copied snippets with no explanation.

Recommended workflow

Step	Why it matters
Preserve the failing request	Record route, method, timestamp and correlation ID without copying credentials or personal data.
Check the proxy layer	Separate upstream connection failures from application-generated 500 responses.
Follow PHP-FPM	Review pool logs, worker limits, timeouts and the effective php.ini for the serving process.
Reproduce safely	Use a non-production request with the same code path and controlled input.

Starter snippet

request id -> web server log -> PHP-FPM log -> application exception

Review checks

Keep display_errors off in production.
Log a safe correlation ID in every layer.
Check disk space and file permissions.
Verify opcache state after deployment.

Common mistakes

Showing stack traces to public clients.
Editing CLI php.ini while PHP-FPM uses another file.
Restarting every service before collecting evidence.

Validation should help users correct input while protecting systems from bad data. Keep syntax checks, product policy, security review and deliverability checks separate.

Related Formalint references

Continue with Php Fpm Nginx Debugging Guide, Nginx 502 504 Debugging Guide, Php Ini Configuration Guide.