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✦ Tips & Best Practices/2026-03-30Advanced

Antigravity × Custom Code Generator — Building Project-Specific Code Generation Pipelines with Template Engines + AI Agents

Learn how to build custom code generators by combining Antigravity's AI agents with template engines. Master Hygen, Plop, and custom TypeScript scaffolding integrated with AGENTS.md to elevate your team's code quality and productivity.

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Setup and context — Why You Need Your Own Code Generator

As projects grow, you'll find yourself repeatedly creating the same file structures — API endpoints, React components, database migrations, test files. When done manually each time, it's not just slow; it leads to subtle inconsistencies as different team members interpret patterns differently.

Antigravity's AI agent can generate code that follows your project's conventions, but relying solely on prompts means repeating the same instructions and dealing with inconsistent outputs. This is where the combination of template engines and AI agents becomes powerful.

Template engines handle the "structure" while AI agents provide "context-aware logic." This two-layer architecture lets you build code generation pipelines tailored specifically to your project. In this guide, we'll walk through comparing major template engines, integrating them with Antigravity's AGENTS.md and custom rules, and building a fully working TypeScript generator from scratch.

Choosing a Template Engine — Hygen vs. Plop vs. Custom Scripts

The first decision when building a code generator is which template engine to use. Let's compare the three main approaches.

Hygen — File-Based Simplicity

Hygen is a generator that works by simply placing template files in your file system. It has a low learning curve and is well-suited for small to mid-sized projects.

# Install and set up Hygen
npm install -g hygen
hygen init self
 
# Create a template
# _templates/component/new/index.tsx.ejs.t
// _templates/component/new/index.tsx.ejs.t
---
to: src/components/<%= name %>/<%= name %>.tsx
---
import React from 'react';
 
interface <%= name %>Props {
  /** Component description */
  children?: React.ReactNode;
}
 
/**
 * <%= name %> component
 * Auto-generated: <%= new Date().toISOString().split('T')[0] %>
 */
export const <%= name %>: React.FC<<%= name %>Props> = ({ children }) => {
  return (
    <div className="<%= h.changeCase.paramCase(name) %>">
      {children}
    </div>
  );
};
 
export default <%= name %>;

Hygen's strength is that templates live as plain files in your repository, making code review and version control straightforward.

Plop — Interactive Prompt-Driven Generation

Plop generates code through interactive prompts, gathering input from the user. It excels when you need complex conditional branching.

// plopfile.ts
import { NodePlopAPI } from 'plop';
 
export default function (plop: NodePlopAPI) {
  plop.setGenerator('api-endpoint', {
    description: 'Generate a REST API endpoint',
    prompts: [
      {
        type: 'input',
        name: 'resource',
        message: 'Resource name (e.g., users, products):',
      },
      {
        type: 'checkbox',
        name: 'methods',
        message: 'HTTP methods to generate:',
        choices: ['GET', 'POST', 'PUT', 'DELETE'],
      },
      {
        type: 'confirm',
        name: 'withAuth',
        message: 'Include authentication middleware?',
        default: true,
      },
    ],
    actions: (data) => {
      const actions = [
        {
          type: 'add',
          path: 'src/api/{{dashCase resource}}/route.ts',
          templateFile: 'templates/api-route.hbs',
        },
        {
          type: 'add',
          path: 'src/api/{{dashCase resource}}/schema.ts',
          templateFile: 'templates/api-schema.hbs',
        },
      ];
      // Only generate test file when methods are selected
      if (data && data.methods && data.methods.length > 0) {
        actions.push({
          type: 'add',
          path: 'src/api/{{dashCase resource}}/route.test.ts',
          templateFile: 'templates/api-test.hbs',
        });
      }
      return actions;
    },
  });
}

Custom TypeScript Scripts — When You Need Full Control

For large-scale projects or specialized requirements, building a generator from scratch in TypeScript gives you complete flexibility.

// scripts/generate.ts
import { mkdir, writeFile, readFile } from 'fs/promises';
import { join } from 'path';
import Handlebars from 'handlebars';
 
interface GeneratorConfig {
  name: string;
  category: 'component' | 'api' | 'hook' | 'service';
  options: {
    withTests: boolean;
    withStorybook: boolean;
    withStyles: boolean;
  };
}
 
async function generate(config: GeneratorConfig): Promise<void> {
  const templateDir = join(__dirname, '../templates', config.category);
  const outputDir = join(__dirname, '../src', config.category + 's', config.name);
 
  await mkdir(outputDir, { recursive: true });
 
  // Load and compile the template
  const templateSource = await readFile(
    join(templateDir, 'index.hbs'),
    'utf-8'
  );
  const template = Handlebars.compile(templateSource);
 
  // Build context
  const context = {
    name: config.name,
    pascalName: toPascalCase(config.name),
    kebabName: toKebabCase(config.name),
    timestamp: new Date().toISOString(),
    ...config.options,
  };
 
  // Generate files
  const output = template(context);
  await writeFile(join(outputDir, 'index.tsx'), output);
 
  console.log(`✅ Generated ${config.category}: ${config.name}`);
}
 
function toPascalCase(str: string): string {
  return str.replace(/(^\w|-\w)/g, (match) =>
    match.replace('-', '').toUpperCase()
  );
}
 
function toKebabCase(str: string): string {
  return str.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase();
}
 
// Usage:
// npx tsx scripts/generate.ts --name=UserProfile --category=component --withTests

As a general rule: choose Hygen for a handful of simple templates, Plop when you need interactive generation flows, and custom TypeScript scripts when you need complete control.

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✦Master the integration patterns between template engines (Hygen/Plop) and AI agents systematically
✦Build organization-wide code generation pipelines using AGENTS.md and custom rules
✦Get working TypeScript generator implementations with complete testing strategies
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