SpringDoc OpenAPI setup in Spring Boot - Performance & Optimization

Performance: SpringDoc OpenAPI setup

MEDIUM IMPACT

This affects the initial page load speed of the API documentation UI and the backend response time for OpenAPI JSON generation.

Setting up SpringDoc OpenAPI for API documentation

Spring Boot

springdoc:
  packages-to-scan: com.example.api
  api-docs:
    path: /v3/api-docs
  swagger-ui:
    enabled: true

# Limits scanning to API packages only

Restricting package scanning reduces startup time and API docs size, speeding up UI load and backend response.

📈 Performance Gainreduces startup delay by 150-400ms; cuts API docs JSON size by 40-80kb

Setting up SpringDoc OpenAPI for API documentation

Spring Boot

springdoc:
  api-docs:
    path: /v3/api-docs
  swagger-ui:
    enabled: true

# No package filtering, scans entire application including unused classes

Scanning the entire application context causes slower startup and larger OpenAPI JSON, increasing UI load time.

📉 Performance Costblocks backend startup for 200-500ms extra; increases API docs JSON size by 50-100kb

Performance Comparison

Pattern	Backend Startup Delay	API Docs JSON Size	Frontend Load Impact	Verdict
Scan entire app packages	200-500ms extra	100-150kb	LCP +300-600ms	[X] Bad
Scan only API packages	50-150ms extra	20-50kb	LCP +50-150ms	[OK] Good
Swagger UI always enabled	N/A	N/A	Adds 200-300kb bundle, LCP +300-600ms	[X] Bad
Swagger UI enabled only in dev	N/A	N/A	Saves 200-300kb bundle, faster LCP	[OK] Good

Rendering Pipeline

SpringDoc generates OpenAPI JSON on backend startup or on-demand, which the Swagger UI frontend fetches and renders. Large JSON or unnecessary scanning delays backend response and increases frontend load time.

→Backend Startup

→Network Transfer

→Frontend Rendering

⚠️ BottleneckBackend Startup and Network Transfer of large OpenAPI JSON

Core Web Vital Affected

LCP

This affects the initial page load speed of the API documentation UI and the backend response time for OpenAPI JSON generation.

Optimization Tips

1Limit SpringDoc package scanning to only API packages to reduce startup delay.

2Disable Swagger UI in production to avoid loading heavy frontend assets.

3Monitor OpenAPI JSON size and backend response time to optimize LCP.

Performance Quiz - 3 Questions

How does scanning the entire application for OpenAPI documentation affect performance?

A Increases backend startup time and API docs size, slowing UI load

B Reduces backend startup time by caching all classes

C Has no impact on performance

D Improves frontend rendering speed

DevTools: Network and Performance panels

How to check: Open DevTools, reload Swagger UI page, check Network tab for /v3/api-docs JSON size and load time; use Performance tab to measure LCP and scripting time.

What to look for: Look for large JSON payloads and long backend response times; high LCP or long scripting times indicate performance issues.