Network Inspection Skill

Systematic approach to analyzing network requests using Chrome DevTools MCP.

HTTP Status Code Reference

Success (2xx)

Code	Meaning	Notes
200	OK	Standard success response
201	Created	Resource successfully created
204	No Content	Success, no body returned

Redirect (3xx)

Code	Meaning	Debugging Action
301	Moved Permanently	Update hardcoded URLs
302	Found (Temporary)	Check redirect logic
304	Not Modified	Cache is working correctly

Client Error (4xx)

Code	Meaning	Debugging Action
400	Bad Request	Check request payload/parameters
401	Unauthorized	Check auth token/session
403	Forbidden	Check permissions/roles
404	Not Found	Check URL/endpoint spelling
405	Method Not Allowed	Check HTTP method (GET/POST/etc)
409	Conflict	Check for duplicate data
422	Unprocessable Entity	Check validation errors in response
429	Too Many Requests	Implement rate limiting/retry

Server Error (5xx)

Code	Meaning	Debugging Action
500	Internal Server Error	Check backend logs
502	Bad Gateway	Check proxy/load balancer
503	Service Unavailable	Check server health
504	Gateway Timeout	Check backend performance

Network Request Analysis Workflow

1. List All Requests

Use Chrome DevTools MCP to list network requests:

Tool: mcp__chrome-devtools__list_network_requests

2. Filter by Status

Focus on failures first:

1. 5xx errors - Server issues (highest priority)
2. 4xx errors - Client issues (request problems)
3. Slow requests - Performance issues
4. Successful requests - Verify data is correct

3. Inspect Specific Request

Get detailed information:

Tool: mcp__chrome-devtools__get_network_request
Parameters: { "requestId": "request-id-here" }

4. Analyze Request Components

For each problematic request, examine:

• URL - Is the endpoint correct?
• Method - GET, POST, PUT, DELETE?
• Headers - Authorization, Content-Type?
• Body - Request payload format?
• Response - What did server return?

Request Headers to Check

Outgoing Request Headers

Header	Purpose	Debug Value
Authorization	Auth token	Verify token format, expiry
Content-Type	Payload format	Match API expectation
Accept	Response format	application/json typically
Origin	CORS source	Check against allowed origins
Cookie	Session data	Verify session exists

Response Headers to Check

Header	Purpose	Debug Value
Set-Cookie	Session management	Check cookie attributes
X-Request-Id	Request tracking	Use for backend log correlation
Content-Type	Response format	Verify expected format
Cache-Control	Caching policy	Check if stale data issue
WWW-Authenticate	Auth challenge	Details on auth failure

Common API Issues

Authentication Problems

Symptom	Possible Cause	Solution
401 on all requests	Token expired	Refresh token
401 on some requests	Missing token header	Check auth interceptor
403 after login	Insufficient permissions	Check user roles
Redirect to login	Session expired	Re-authenticate

Data Issues

Symptom	Possible Cause	Solution
Empty response	No data found	Check query parameters
Partial data	Pagination	Check for next page
Stale data	Caching	Clear cache, check headers
Wrong data format	API version mismatch	Check API version

CORS Issues

Error	Cause	Solution
No 'Access-Control-Allow-Origin'	Server not configured	Add CORS headers on backend
Preflight failed	OPTIONS request blocked	Allow OPTIONS method
Credentials not supported	withCredentials mismatch	Configure credentials mode

Performance Analysis

Timing Breakdown

Phase	Description	Concern Threshold
DNS Lookup	Domain resolution	> 100ms
Connection	TCP handshake	> 100ms
TLS	SSL negotiation	> 100ms
Request	Sending data	> 500ms
Waiting (TTFB)	Server processing	> 500ms
Response	Receiving data	Depends on payload

Slow Request Causes

Phase Slow	Likely Cause	Solution
DNS	DNS server issues	Use faster DNS
Connection	Server overloaded	Scale infrastructure
TLS	Certificate chain	Optimize SSL config
Waiting	Slow backend	Optimize API/database
Response	Large payload	Paginate, compress

Debugging Report Template

## Network Debugging Report

**URL**: [page URL]
**Date**: [timestamp]
**Total Requests**: [count]

### Summary

- Failed Requests: X (Y% failure rate)
- Slow Requests (>1s): Z
- Total Data Transferred: N MB

### Failed Requests

| Endpoint | Method | Status | Error |
|----------|--------|--------|-------|
| [URL] | [GET/POST] | [code] | [message] |

### Request Analysis

#### Request 1: [endpoint]

**Status**: [code] [status text]

**Request**:
- Method: [method]
- URL: [full URL]
- Headers:

[relevant headers]

- Body:
```json
[request body]

Response:

• Status: [code]
• Headers:

  [relevant headers]
  

• Body:

  [response body or error]
  

Analysis: [what went wrong]

Suggested Fix: [recommendation]

Performance Issues

Endpoint	TTFB	Total Time	Issue
[URL]	[ms]	[ms]	[analysis]

Recommendations

1. [prioritized action 1]
2. [prioritized action 2]

## Integration with Console Debugging

Network failures often cause console errors:

| Network Issue | Console Manifestation |
|---------------|----------------------|
| 401 Unauthorized | `Error: User not authenticated` |
| 404 Not Found | `Error: Resource not found` |
| 500 Server Error | `Error: Request failed` |
| Network offline | `TypeError: Failed to fetch` |
| CORS blocked | CORS error message |

Use `console-debugging` skill alongside for comprehensive debugging.

## Best Practices

1. **Check the obvious first** - Is the URL correct? Is the server running?
2. **Compare working vs broken** - What's different about failing requests?
3. **Test in isolation** - Use curl/Postman to eliminate frontend issues
4. **Check request order** - Are dependent requests happening in right order?
5. **Verify authentication flow** - Token refresh, session expiry?
6. **Look at full response** - Error details often in response body