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I Built a Mock Server in Go with 24x Performance Boost

2026-03-12 • 8 min read

As a full-stack developer, I work with APIs every day. Frontend waiting for backend, third-party API rate limits, microservice coordination... all these scenarios need mock data.

I've tried many mock tools, but something always felt off:

  • MockServer: Powerful but heavy, requires JVM
  • JSON Server: Lightweight but only REST, no dynamic responses
  • Postman Mock: Requires internet, paid for team collaboration

So I decided to build my own. The goal was simple:

Zero dependencies, single binary, full-featured, high-performance

Three months later, MockAPI was born.

Results at a Glance

MetricValue
Runtime Dependencies0
Installationgo install one command
Startup Time< 100ms
Route Matching24x faster
Memory Usage94% less

Features:

  • ✅ REST Mock (dynamic routes, path params, wildcards, conditional responses)
  • ✅ GraphQL Mock
  • ✅ WebSocket Mock
  • ✅ gRPC-Web Mock
  • ✅ JavaScript scripting engine
  • ✅ Swagger/OpenAPI import
  • ✅ Built-in Web UI
  • ✅ Hot reload

Why Go?

I chose Go not because I only know Go (though that's partly true), but because it fits perfectly:

1. Zero Runtime Dependencies

Compile to a single binary. Users don't need Node.js, JVM, or any other runtime. Download and run.

2. Powerful Standard Library

Go's net/http is fast, encoding/json is sufficient, embed lets you embed the Web UI in the binary.

3. Cross-Platform Compilation

Compile once, run everywhere.

4. Simple Deployment

No complex dependencies, deploy without Docker.

Performance: From O(n) to O(1)

Initially, route matching was linear search. Performance degraded as routes increased.

Solution: RouteIndex

I designed a two-layer index structure:

  • Exact match: Direct map lookup, O(1)
  • Param routes: Grouped by prefix, reduces candidates
  • Wildcard routes: Grouped by method

Results

24x faster, 94% less memory. That's the power of choosing the right data structure.

Core Features

Dynamic Routes

Support :param and * wildcards.

JavaScript Engine

Generate dynamic responses with JavaScript when static isn't enough.

Swagger/OpenAPI Import

Import existing API docs, auto-generate mock routes.

Built-in Web UI

Manage in browser: http://localhost:8088/_ui

Features: Route management, visual editor, quick templates, request logs, real-time debugging.

Quick Start

# Install
go install github.com/fynntang/MockAPI@latest

# Run
mockapi serve

Project Links

  • GitHub: https://github.com/fynntang/MockAPI
  • Website: https://mockapi.work

If this project helps you, please Star ⭐

Final Thoughts

Building MockAPI taught me:

  1. Simplicity wins - Zero dependencies beats feature bloat
  2. Performance early - Good data structures beat late optimization
  3. Developer experience matters - CLI and Web UI improve usability
  4. Test-driven - 26 tests let me sleep well

Happy Mocking! 🦞

enzh-hans