/nextjs-tanstack-form

name: nextjs-tanstack-form
description: Use when building forms in Next.js 16 with TanStack Form v1 — Server Actions, Zod validation, multi-step wizards, field arrays.
versions:
  tanstack-form: 1.0
  nextjs: 16
  react: 19
  zod: 3.24
user-invocable: true
references: references/installation.md, references/basic-usage.md, references/field-api.md, references/form-state.md, references/validation-zod.md, references/server-actions.md, references/array-fields.md, references/async-validation.md, references/shadcn-integration.md, references/typescript.md, references/multi-step-form.md, references/performance.md, references/testing.md, references/migration-rhf.md
related-skills: nextjs-16, nextjs-shadcn, solid-nextjs

<objective> Implements TanStack Form v1 in Next.js 16 with native Server Actions integration: shared `formOptions` (single source of truth for client and server), Zod schemas for both instant client feedback and `onServerValidate` database checks, `useActionState` for the React 19 form-submission hook, and `mergeForm` to combine server-returned errors with client state.

Covers the Field API (state + handlers), validation timing (onChange/onBlur/onSubmit/onServer), dynamic field arrays and multi-step wizards, debounced async validation, and shadcn/ui field composition. Also documents SOLID file organization for forms (`form-options.ts`, `FormComponent.tsx`, `form.action.ts`) and a comparison against React Hook Form. This is the Next.js Server Actions variant of TanStack Form — for a plain React app without Next.js see the react-forms skill. </objective>

TanStack Form for Next.js 16

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

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one `Agent` call each with a `name`:

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.

---

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/`

---

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](references/installation.md) | | Basic patterns | [basic-usage.md](references/basic-usage.md), [field-api.md](references/field-api.md) | | Validation | [validation-zod.md](references/validation-zod.md), [async-validation.md](references/async-validation.md) | | Server Actions | [server-actions.md](references/server-actions.md) | | Dynamic forms | [array-fields.md](references/array-fields.md), [multi-step-form.md](references/multi-step-form.md) | | UI integration | [shadcn-integration.md](references/shadcn-integration.md) | | TypeScript | [typescript.md](references/typescript.md) | | Migration | [migration-rhf.md](references/migration-rhf.md) | | Client-side form component | [client-form.md](references/client-form.md) — load when wiring `useActionState` + `mergeForm` in a `'use client'` form component | | Server-side validation | [server-validation.md](references/server-validation.md) — load when writing `createServerValidate` + `ServerValidateError` in a Server Action |

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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 `merge