How to Debug APIs in PHP: Complete Guide (Trace, Replay, CLI)

Debugging APIs in PHP doesn't have to be a nightmare. Whether you're dealing with a 500 Internal Server Error or an unexpected response payload, the right debugging workflow can save you hours of frustration.

SiroPHP is a lightweight PHP API framework designed specifically for developers who need to debug production APIs quickly. With built-in request tracing, replay functionality, and CLI testing tools, you can fix bugs in minutes instead of hours.

In this complete guide, you'll learn how to debug PHP APIs in production using three powerful techniques: request tracing, request replay, and CLI testing. By the end, you'll have a battle-tested workflow for fixing API bugs fast.

1. Understand the Problem

Before you can debug an API, you need to understand what's happening. Common PHP API issues include:

• 500 errors - Server-side exceptions or syntax errors
• 404 errors - Route not found or misconfigured
• 401/403 errors - Authentication or authorization failures
• Unexpected payloads - Data transformation issues
• Timeout errors - Slow database queries or external API calls

2. Request Tracing: Find What Went Wrong

Request tracing is your first line of defense. Every API request should have a unique trace ID that follows it through your entire application stack.

When an error occurs, you can extract the trace ID from the response headers and use it to find:

• Complete request/response cycle
• Database queries executed
• External API calls made
• Error stack traces
• Timing information for each step

# Extract trace ID from error response
curl -v https://api.yoursite.com/users

# Look for header:
X-Siro-Trace-Id: siro_abc123def456

# View full trace
php siro log:trace siro_abc123def456

3. Request Replay: Reproduce Instantly

Here's where it gets powerful. Instead of trying to manually reproduce the bug (which often fails), you can replay the exact requestthat caused the error.

Request replay captures:

• Exact request payload and headers
• Authentication state
• Environment variables
• Database state at the time of request

# Replay the exact request that failed
php siro log:replay siro_abc123def456

# Output:
Replaying request: POST /api/users
Status: 200 OK (after fix applied)
Response: {"id": 123, "name": "John Doe"}

Debugging time: 3 minutes ✓

4. CLI Testing: Verify Your Fix

After applying your fix, you need to verify it works. CLI testing lets you test API endpoints directly from your terminal without leaving your workflow.

# Test endpoint with auto-authentication
php siro api:test POST /api/users   --data '{"name":"Jane","email":"jane@test.com"}'

# Output:
✓ POST /api/users
✓ Status: 201 Created
✓ Response time: 45ms
✓ Validation passed
✓ User created successfully

The best part? CLI testing includes automatic authentication, so you don't need to manually handle tokens or sessions.

5. Best Practices for API Debugging