Building Fast AI Agents: Regex Search + Cheap Inference API (Full Stack Guide)

Published: March 28, 2026 | Inspired by: Cursor — Fast regex search for agent tools

The Cost That Kills Agent Projects

The Complete Fast Agent Stack: Python

# pip install nexaapi
import re
from nexaapi import NexaAPI

client = NexaAPI(api_key='YOUR_API_KEY')

class FastAIAgent:
    def __init__(self):
        # Pre-compile regex patterns for speed (O(n) text scan)
        self.patterns = {
            'image': re.compile(r'generate|create|draw|design|visualize', re.I),
            'audio': re.compile(r'speak|narrate|voice|audio|tts', re.I),
            'video': re.compile(r'animate|video|motion|clip', re.I),
        }
    
    def fast_route(self, user_input: str):
        """Fast regex routing — no LLM needed for intent detection"""
        if self.patterns['image'].search(user_input):
            return self._generate_image(user_input)
        elif self.patterns['audio'].search(user_input):
            return self._generate_audio(user_input)
        else:
            return self._llm_inference(user_input)
    
    def _generate_image(self, prompt: str):
        # NexaAPI: $0.003/image — 13x cheaper than DALL-E 3
        response = client.images.generate(
            model='flux-schnell',
            prompt=prompt,
            width=1024, height=1024
        )
        return {'type': 'image', 'url': response.data[0].url, 'cost': '$0.003'}
    
    def _generate_audio(self, text: str):
        response = client.audio.speech.create(model='tts-1', input=text, voice='alloy')
        return {'type': 'audio', 'url': response.url}
    
    def _llm_inference(self, prompt: str):
        response = client.chat.completions.create(
            model='gpt-4o-mini',
            messages=[{'role': 'user', 'content': prompt}]
        )
        return {'type': 'text', 'content': response.choices[0].message.content}

agent = FastAIAgent()
result = agent.fast_route('Generate a futuristic city skyline at night')
print(f"Cost: {result['cost']}")  # $0.003 — 13x cheaper than DALL-E 3

JavaScript Version

// npm install nexaapi
import NexaAPI from 'nexaapi';

const client = new NexaAPI({ apiKey: 'YOUR_API_KEY' });

class FastAIAgent {
  constructor() {
    this.patterns = {
      image: /generate|create|draw|design|visualize/gi,
      audio: /speak|narrate|voice|audio|tts/gi,
    };
  }
  
  async fastRoute(userInput) {
    Object.values(this.patterns).forEach(p => p.lastIndex = 0);
    
    if (this.patterns.image.test(userInput)) {
      const response = await client.images.generate({
        model: 'flux-schnell', prompt: userInput, width: 1024, height: 1024
      });
      return { type: 'image', url: response.data[0].url, cost: '$0.003' };
    }
    
    const response = await client.chat.completions.create({
      model: 'gpt-4o-mini',
      messages: [{ role: 'user', content: userInput }]
    });
    return { type: 'text', content: response.choices[0].message.content };
  }
}

const agent = new FastAIAgent();
const result = await agent.fastRoute('Generate a futuristic city at night');
console.log(result.cost); // $0.003