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jpoutrin

network-inspection

by jpoutrin

Claude Code Marketplace Plugin to dev like a pro in a multi-agent fashion

4🍴 0📅 2026年1月22日
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SKILL.md


name: network-inspection description: HTTP request and response analysis for debugging API calls, identifying failed requests, and understanding data flow. Use when investigating API issues, authentication problems, or data loading failures.

Network Inspection Skill

Systematic approach to analyzing network requests using Chrome DevTools MCP.

HTTP Status Code Reference

Success (2xx)

CodeMeaningNotes
200OKStandard success response
201CreatedResource successfully created
204No ContentSuccess, no body returned

Redirect (3xx)

CodeMeaningDebugging Action
301Moved PermanentlyUpdate hardcoded URLs
302Found (Temporary)Check redirect logic
304Not ModifiedCache is working correctly

Client Error (4xx)

CodeMeaningDebugging Action
400Bad RequestCheck request payload/parameters
401UnauthorizedCheck auth token/session
403ForbiddenCheck permissions/roles
404Not FoundCheck URL/endpoint spelling
405Method Not AllowedCheck HTTP method (GET/POST/etc)
409ConflictCheck for duplicate data
422Unprocessable EntityCheck validation errors in response
429Too Many RequestsImplement rate limiting/retry

Server Error (5xx)

CodeMeaningDebugging Action
500Internal Server ErrorCheck backend logs
502Bad GatewayCheck proxy/load balancer
503Service UnavailableCheck server health
504Gateway TimeoutCheck 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

HeaderPurposeDebug Value
AuthorizationAuth tokenVerify token format, expiry
Content-TypePayload formatMatch API expectation
AcceptResponse formatapplication/json typically
OriginCORS sourceCheck against allowed origins
CookieSession dataVerify session exists

Response Headers to Check

HeaderPurposeDebug Value
Set-CookieSession managementCheck cookie attributes
X-Request-IdRequest trackingUse for backend log correlation
Content-TypeResponse formatVerify expected format
Cache-ControlCaching policyCheck if stale data issue
WWW-AuthenticateAuth challengeDetails on auth failure

Common API Issues

Authentication Problems

SymptomPossible CauseSolution
401 on all requestsToken expiredRefresh token
401 on some requestsMissing token headerCheck auth interceptor
403 after loginInsufficient permissionsCheck user roles
Redirect to loginSession expiredRe-authenticate

Data Issues

SymptomPossible CauseSolution
Empty responseNo data foundCheck query parameters
Partial dataPaginationCheck for next page
Stale dataCachingClear cache, check headers
Wrong data formatAPI version mismatchCheck API version

CORS Issues

ErrorCauseSolution
No 'Access-Control-Allow-Origin'Server not configuredAdd CORS headers on backend
Preflight failedOPTIONS request blockedAllow OPTIONS method
Credentials not supportedwithCredentials mismatchConfigure credentials mode

Performance Analysis

Timing Breakdown

PhaseDescriptionConcern Threshold
DNS LookupDomain resolution> 100ms
ConnectionTCP handshake> 100ms
TLSSSL negotiation> 100ms
RequestSending data> 500ms
Waiting (TTFB)Server processing> 500ms
ResponseReceiving dataDepends on payload

Slow Request Causes

Phase SlowLikely CauseSolution
DNSDNS server issuesUse faster DNS
ConnectionServer overloadedScale infrastructure
TLSCertificate chainOptimize SSL config
WaitingSlow backendOptimize API/database
ResponseLarge payloadPaginate, 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

EndpointTTFBTotal TimeIssue
[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

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