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.
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 Hygennpm install -g hygenhygen 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.
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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WHAT YOU'LL LEARN
✦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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Integration Architecture with Antigravity AI Agents
Template engines alone produce "static scaffolds." By integrating Antigravity's AI agent, you unlock context-aware, intelligent code generation.
The Two-Layer Architecture
┌─────────────────────────────────────────────┐
│ User Request (Natural Language) │
│ "Create an API endpoint with auth and │
│ validation" │
└───────────────┬─────────────────────────────┘
│
┌───────────▼───────────┐
│ Antigravity AI Agent │ ← Context + Judgment
│ (References AGENTS.md)│
└───────────┬───────────┘
│ Determines parameters
┌───────────▼───────────┐
│ Template Engine │ ← Structural guarantee
│ (Hygen / Plop) │
└───────────┬───────────┘
│ File generation
┌───────────▼───────────┐
│ AI Post-Processing │ ← Context-specific logic
│ (Type inference, etc.)│
└───────────────────────┘
In this two-layer architecture, templates generate the "skeleton" and the AI agent provides the "flesh." Templates guarantee file naming conventions, directory structure, import path consistency, and boilerplate uniformity. The AI agent handles business logic implementation, edge case handling, type definition optimization, and documentation comments.
Defining Generator Rules in AGENTS.md
By embedding code generation guidelines in Antigravity's AGENTS.md, the AI agent understands your templates' intent when generating or modifying code.
<!-- AGENTS.md (excerpt) -->## Code Generation Guidelines### Required Rules for File Generation1. Create new components via `scripts/generate.ts`2. When creating files directly, follow existing template patterns3. Always run `npm run lint:fix` after generation### Naming Conventions- Components: PascalCase (e.g., UserProfile)- File names: kebab-case (e.g., user-profile.tsx)- Test files: *.test.ts / *.spec.ts- Hooks: use + PascalCase (e.g., useUserProfile)### Template Locations- Components: `_templates/component/`- API routes: `_templates/api/`- Hooks: `_templates/hook/`- Services: `_templates/service/`### Post-Generation Checklist- [ ] No TypeScript type errors- [ ] No ESLint warnings- [ ] Corresponding test file exists- [ ] Added to index.ts exports
With these definitions in AGENTS.md, when a team member tells Antigravity to "create a new component," the agent automatically follows the generator's rules.
Implementation — Building a React Component Generator
Let's build a working component generator in TypeScript, showing the template-AI integration in practice.
Controlling Generation Quality with Custom Rule Files
By placing custom rules in Antigravity's .antigravity/rules/ directory, you can precisely control the guidelines the AI agent references during code generation.
<!-- .antigravity/rules/code-generation.md --># Code Generation Rules## Component Generation- All components must use the `React.FC<Props>` type- Props interfaces must always be exported- No default exports (named exports only)- When using CSS Modules, class names follow BEM notation## Test Generation- Use Vitest as the test framework- Follow `describe` > `it` nesting structure- Use `@testing-library/react`'s `render` and `screen`## API Route Generation- Zod schema validation is mandatory- Error responses must follow RFC 7807 format- Always include rate limiting middleware
With this rule file in place, here's how Antigravity's agent behaves:
User: "Create a UserSettings component"
Antigravity Agent's thought process:
1. Load code-generation.md rules
2. Check _templates/component/ templates
3. Analyze existing component patterns
4. Generate with React.FC<Props> + named exports per rules
5. Simultaneously generate Vitest test file
Template Versioning and Evolution Strategy
Templates aren't "set and forget." You need systems to evolve them alongside your project.
Template Validation
Prepare a script to verify templates aren't broken, and run it in CI.
Before modifying a template, an impact analysis script helps assess which generated files would be affected.
// scripts/analyze-template-impact.tsimport { readdir, readFile } from 'fs/promises';import { join, relative } from 'path';async function analyzeImpact(templateName: string): Promise<void> { // Track template versions through header comments // in generated files const srcDir = join(__dirname, '../src'); const generatedFiles = await findGeneratedFiles(srcDir); console.log(`Files generated from template "${templateName}":`); console.log(`Total: ${generatedFiles.length} files`); for (const file of generatedFiles) { const relPath = relative(process.cwd(), file.path); console.log(` ${relPath} (v${file.templateVersion})`); }}interface GeneratedFileInfo { path: string; templateVersion: string; generatedAt: string;}async function findGeneratedFiles(dir: string): Promise<GeneratedFileInfo[]> { // Generated files contain this header: // // @generated by template v1.2.0 at 2026-03-30 const results: GeneratedFileInfo[] = []; const entries = await readdir(dir, { withFileTypes: true, recursive: true }); for (const entry of entries) { if (!entry.isFile() || !entry.name.endsWith('.tsx')) continue; const filePath = join(dir, entry.name); const content = await readFile(filePath, 'utf-8'); const match = content.match( /@generated by template v([\d.]+) at ([\d-]+)/ ); if (match) { results.push({ path: filePath, templateVersion: match[1], generatedAt: match[2], }); } } return results;}
Dynamic Template Extension with AI Agents
Static templates can't handle every case. For instance, generating TypeScript interfaces from an external API's schema requires intelligence beyond what templates offer. This is where Antigravity's AI agent steps in.
Pattern 1: Schema-Driven Code Generation
// scripts/schema-driven-generate.tsimport { readFile, writeFile } from 'fs/promises';import { join } from 'path';/** * Generate API clients from an OpenAPI schema. * Antigravity's agent analyzes the schema and * generates type-safe client code. */async function generateFromSchema( schemaPath: string): Promise<void> { const schema = JSON.parse( await readFile(schemaPath, 'utf-8') ); // Generate client functions for each endpoint for (const [path, methods] of Object.entries(schema.paths)) { const endpoint = methods as Record<string, unknown>; for (const [method, config] of Object.entries(endpoint)) { const operationId = (config as { operationId?: string }).operationId; if (!operationId) continue; // Instructions for AI agent // Generates type definitions following AGENTS.md rules const typeDefinition = generateTypeFromSchema( config as Record<string, unknown> ); console.log( `Generated: ${method.toUpperCase()} ${path} -> ${operationId}` ); } }}function generateTypeFromSchema( config: Record<string, unknown>): string { // The AI agent dynamically fills this part // Templates provide only the skeleton return '// AI agent generates type definitions';}
Pattern 2: Learning Patterns from Existing Code
Antigravity's agent can analyze your existing codebase and learn project-specific patterns. Leverage this to dynamically improve your templates.
<!-- Example instruction for Antigravity -->Analyze src/components/ in this project and extractthe following patterns:1. Most frequently used React hook combinations2. Prop naming patterns (on* event handlers, etc.)3. Error handling patterns4. Comment / JSDoc conventionsOutput the results to _templates/component/patterns.json.
This approach makes templates "living documents" that continuously adapt to your project's actual patterns.
Testing Strategy — Testing the Generator Itself
A code generator produces other code, so you need a testing strategy that verifies the "generated code is correct."
In this guide, we explored how to build custom code generators by combining Antigravity's AI agents with template engines. Templates ensure "structural consistency" while AI agents provide "context-aware intelligent completion," together elevating your entire team's code quality and development speed.
Start small — perhaps a single component template — and add guidelines to AGENTS.md and .antigravity/rules/. For a deep dive into AGENTS.md design, check out our Antigravity Context Design Complete Guide. To master custom rules, see Antigravity Custom Rules & Project Config Mastery Guide. If you want to distribute your generator as a CLI tool, Building Professional CLI Tools with Antigravity is an excellent resource. As your template collection grows, introduce validation scripts and CI integration, evolving your generator alongside your project.
To deepen your understanding of code generation pipeline design,
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