TanStack Form for Next.js 16

Type-safe, performant forms with Server Actions and signal-based reactivity.

Agent Workflow (MANDATORY)

Before ANY implementation, use TeamCreate to spawn 3 agents:

1. fuse-ai-pilot:explore-codebase - Analyze existing forms and validation patterns
2. fuse-ai-pilot:research-expert - Verify latest TanStack Form docs via Context7/Exa
3. mcp__context7__query-docs - Check form options and field API

After implementation, run fuse-ai-pilot:sniper for validation.

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Overview

When to Use

• Building forms with complex validation requirements
• Need Server Actions integration for form submission
• Implementing multi-step wizards or dynamic field arrays
• Require real-time async validation (username availability)
• Want type-safe forms with full TypeScript inference

Why TanStack Form

Feature	Benefit
Signal-based state	Minimal re-renders, optimal performance
Full TypeScript	DeepKeys, DeepValue inference
Server Actions native	Built-in Next.js 16 integration
Zod adapter	Schema-first validation
Framework agnostic	Same API for React, Vue, Solid
Headless	Works with any UI library (shadcn/ui)

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Critical Rules

1. formOptions shared - Define once, use in client and server
2. Server validation - DB checks in onServerValidate, not client
3. Zod schemas - Client-side instant feedback
4. useActionState - React 19 hook for Server Actions
5. mergeForm - Combine server errors with client state
6. SOLID paths - Forms in modules/[feature]/src/components/forms/

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SOLID Architecture

Module Structure

Forms organized by feature module:

• modules/auth/src/components/forms/ - Auth forms (login, signup)
• modules/auth/src/interfaces/ - Form types and schemas
• modules/auth/src/actions/ - Server Actions for form submission
• modules/cores/lib/forms/ - Shared form utilities

File Organization

File	Purpose	Max Lines
form-options.ts	Shared formOptions + Zod schema	50
FormComponent.tsx	Client form UI with fields	80
form.action.ts	Server Action with validation	30
form.interface.ts	Types for form values	30

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Key Concepts

Form Options Pattern

Define form configuration once, share between client and server. Ensures type safety and consistency.

Field API

Each field has state (value, errors, touched, validating) and handlers (handleChange, handleBlur).

Validation Levels

• onChange - Real-time as user types
• onBlur - When field loses focus
• onSubmit - Before form submission
• onServer - Server-side in action

Error Management

Errors exist at field-level and form-level. Use field.state.meta.errors for field errors, form.state.errorMap for form errors.

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Reference Guide

Need	Reference
Initial setup	installation.md
Basic patterns	basic-usage.md, field-api.md
Validation	validation-zod.md, async-validation.md
Server Actions	server-actions.md
Dynamic forms	array-fields.md, multi-step-form.md
UI integration	shadcn-integration.md
TypeScript	typescript.md
Migration	migration-rhf.md

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Best Practices

1. Define schemas first - Zod schemas drive both validation and types
2. Shared formOptions - Single source of truth for client/server
3. Debounce async validation - Use asyncDebounceMs for API calls
4. form.Subscribe - Selective re-renders for submit state
5. Field composition - Reusable field components with shadcn/ui
6. Server errors merge - Use mergeForm to show server validation errors

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Comparison vs React Hook Form

Aspect	TanStack Form	React Hook Form
Type Safety	100% (DeepKeys)	Manual typing
Performance	Signals (minimal)	Refs (good)
Server Actions	Native support	Manual integration
Bundle Size	~12KB	~9KB
Learning Curve	Medium	Low
Use Case	Complex apps	Standard forms