Mastering Antigravity Plan Mode and Fast Mode — Maximize Development Efficiency with Agent Thinking Modes

Understanding Antigravity's Agent Modes

Antigravity IDE gives you control over how its AI agent approaches tasks through different "thinking modes." The two primary modes are Plan Mode and Fast Mode.

Plan Mode has the agent create a structured plan before writing any code, tackling tasks step by step with your confirmation. Fast Mode, on the other hand, lets the agent respond immediately, generating code and fixes on the fly. Neither mode is inherently better — the key to maximizing your development efficiency is knowing when to use each one.

Plan Mode: Features and Best Use Cases

Plan Mode is designed for tasks that benefit from deliberate, structured thinking before implementation. Here's what makes it stand out:

• Task decomposition: Breaks large tasks into smaller, manageable steps before execution
• Confirmation prompts: Asks for your approval before proceeding with each step
• Dependency analysis: Analyzes inter-file dependencies and identifies the scope of changes
• Rollback awareness: Designs changes with recovery points in mind

Plan Mode really shines in these scenarios:

Large-scale refactoring: When structural changes span multiple files, planning ahead prevents missed updates and inconsistencies.

Designing and building new features: Starting from scratch on a component or module benefits from having the full architectural picture before diving into code.

CI/CD pipeline construction: Building out build, test, and deploy stages requires the kind of systematic approach that Plan Mode naturally provides.

// Example: Using Plan Mode for new feature design
// Prompt to the agent:
// "Add user authentication. Use Plan Mode."
 
// Agent's plan output:
// Step 1: Define auth schema (schema/auth.ts)
// Step 2: Create auth API routes (api/auth/route.ts)
// Step 3: Implement middleware (middleware.ts)
// Step 4: Build frontend auth context (contexts/AuthContext.tsx)
// Step 5: Create login form component (components/LoginForm.tsx)
// Step 6: Write and run tests
 
// The agent confirms each step before moving to the next

Fast Mode: Features and Best Use Cases

Fast Mode prioritizes speed, letting the agent generate code with minimal planning overhead. It's built for rapid iteration:

• Instant responses: Generates code immediately after receiving your prompt
• Iterative development: Optimized for quick "write → test → fix" cycles
• Context awareness: Leverages the current file context for targeted suggestions
• Lower token consumption: Skipping the planning phase saves AI credits

Fast Mode is ideal for these situations:

Bug fixes: When you've identified the error and just need a quick patch, speed matters more than planning.

Small-scope changes: CSS tweaks, text updates, type definition additions — anything where the impact is contained to a file or two.

Prototyping: When you're experimenting with ideas, Plan Mode's deliberation can actually slow you down.

// Example: Using Fast Mode for a quick bug fix
// Prompt to the agent:
// "This component throws an undefined error. Fix it."
 
// Fast Mode generates the fix immediately:
// Before:
const userName = user.profile.name; // user.profile could be undefined
 
// After (agent's instant suggestion):
const userName = user?.profile?.name ?? "Guest";
// Optional chaining with a fallback value for safe access

How to Switch Between Plan Mode and Fast Mode

Antigravity offers several ways to toggle between modes:

Method 1: Command palette

Press Cmd + Shift + P (Mac) or Ctrl + Shift + P (Windows/Linux) to open the command palette, then type "Agent Mode." Select Plan Mode or Fast Mode from the options that appear.

Method 2: Chat panel dropdown

The mode selector dropdown at the top of the agent's chat panel lets you switch modes directly. This is the most intuitive approach.

Method 3: Inline prompt instructions

You can specify the mode directly in your prompt:

Design the authentication system using Plan Mode

Fix this bug in Fast Mode

The agent recognizes mode keywords in your prompts and adjusts its behavior accordingly.

When to Choose Which Mode

If you're unsure which mode to use, these guidelines can help you decide:

Choose Plan Mode when:

• The change touches 3 or more files
• The task will take more than 30 minutes
• Architectural decisions are involved
• You plan to create a PR for team review
• The changes would be difficult to roll back

Choose Fast Mode when:

• Changes are contained to 1–2 files
• The task can be done in under 5 minutes
• The fix is clear (error message already identified)
• You're writing prototype or experimental code
• The work is repetitive (adding tests, extending types, etc.)

In practice, switching modes within a single task is often the most effective approach. For instance, you might use Plan Mode to design a new feature's architecture, then switch to Fast Mode to implement each individual component. This hybrid workflow gives you the best of both worlds.

Practical Example: Designing API Endpoints with Plan Mode

Here's a hands-on example of using Plan Mode to design REST API endpoints:

// Prompt to the agent:
// "Design and implement CRUD endpoints for product management using Plan Mode"
 
// Agent's generated plan:
// ─── Plan ───
// 1. Data model: Define Product type and validation schema
// 2. API routes: Create GET/POST/PUT/DELETE endpoints
// 3. Error handling: Implement unified error responses
// 4. Testing: Write unit tests for each endpoint
 
// Step 1: Data model (types/product.ts)
interface Product {
  id: string;
  name: string;
  price: number;
  description: string;
  createdAt: Date;
  updatedAt: Date;
}
 
// Step 2: API routes (app/api/products/route.ts)
export async function GET(request: Request) {
  const { searchParams } = new URL(request.url);
  const page = parseInt(searchParams.get("page") ?? "1");
  const limit = parseInt(searchParams.get("limit") ?? "20");
 
  const products = await db.product.findMany({
    skip: (page - 1) * limit,
    take: limit,
    orderBy: { createdAt: "desc" },
  });
 
  return Response.json({ products, page, limit });
}
 
export async function POST(request: Request) {
  const body = await request.json();
  // Create after validation
  const product = await db.product.create({ data: body });
  return Response.json(product, { status: 201 });
}

With Plan Mode, the agent confirms each step's completion with you before moving on, so you stay aligned with the design intent throughout implementation.

Practical Example: Instant Styling Fixes with Fast Mode

Here's Fast Mode in action for a quick CSS update:

/* Prompt to the agent:
   "Add hover effects and dark mode support to this card component" */
 
/* Fast Mode generates instantly: */
.card {
  padding: 1.5rem;
  border-radius: 0.75rem;
  background: white;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
 
.card:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}
 
/* Dark mode support */
@media (prefers-color-scheme: dark) {
  .card {
    background: #1e1e2e;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
  }
 
  .card:hover {
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.4);
  }
}

By skipping the planning phase, Fast Mode completes localized changes like this almost instantly.

Looking back

Antigravity's Plan Mode and Fast Mode serve different purposes in your development workflow. Plan Mode excels at complex, multi-file tasks that require careful coordination, while Fast Mode is your go-to for quick fixes, prototyping, and iterative work.

The real productivity gains come from knowing when to switch. Use Plan Mode for the big-picture design work where forethought prevents costly mistakes, and Fast Mode for the hands-on implementation where speed keeps your momentum going. This hybrid approach is what takes AI-driven development to the next level.