Server validation

Validate schemas at build time and submissions at runtime using the core engine — no React required.

Schema validation

The validateSchema function checks a schema for structural errors at build time or on your server. It catches issues that would cause runtime failures.

import { validateSchema } from '@squaredr/fieldcraft-core'try {  const validSchema = validateSchema(rawSchema)  // validSchema is typed as FormEngineSchema} catch (error) {  if (error instanceof FormEngineSchemaError) {    console.error(error.message)    // "Invalid FormEngine schema:    //   - Duplicate question ID: "email"    //   - Section "details" has no questions    //   - Field "notes" is non-input type but has "required" property"  }}

What it checks

Check	Description
Required properties	`id`, `version`, `title`, `sections`, `submitAction` must exist
Section structure	Each section needs `id`, `title`, and at least one question
Unique field IDs	No duplicate `id` values across the entire schema
Non-input validation	Structural/content fields (`info_block`, `divider`, etc.) must not have `required` or `validation`
Condition references	`showIf` field references must point to existing field IDs
Jump rule targets	`onExit.jumpTo` must reference existing section IDs
Option integrity	Choice-based fields must have at least one option

Use cases

CI pipeline — validate schemas in your test suite:

import { validateSchema } from '@squaredr/fieldcraft-core'import schema from './schemas/contact-form.json'test('contact form schema is valid', () => {  expect(() => validateSchema(schema)).not.toThrow()})

API endpoint — validate before saving to a database:

// app/api/schemas/route.tsimport { validateSchema, FormEngineSchemaError } from '@squaredr/fieldcraft-core'export async function POST(req: Request) {  const body = await req.json()  try {    const schema = validateSchema(body)    await db.schemas.insert(schema)    return Response.json({ success: true })  } catch (error) {    if (error instanceof FormEngineSchemaError) {      return Response.json({ error: error.message }, { status: 400 })    }    throw error  }}

Submission validation

Use createEngine server-side to validate submitted data against the schema:

import { createEngine } from '@squaredr/fieldcraft-core'import schema from './schemas/contact-form.json'export async function POST(req: Request) {  const { values } = await req.json()  const engine = createEngine(schema)  // Set submitted values  engine.setValues(values)  // Validate all fields  const result = engine.validate()  if (!result.valid) {    return Response.json({      error: 'Validation failed',      errors: result.errors,      firstErrorFieldId: result.firstErrorFieldId,    }, { status: 422 })  }  // Values are valid — process the submission  await processSubmission(values)  return Response.json({ success: true })}

This uses the same validation logic that runs in the browser — same rules, same error messages. You don't need to duplicate validation on the server.

Core package — no React required

@squaredr/fieldcraft-core has zero UI dependencies. It works in any Node.js or edge runtime:

import { createEngine, validateSchema } from '@squaredr/fieldcraft-core'

Use it for:

Server-side validation of submissions
Schema validation in CI/CD pipelines
Pre-processing schemas before storing in a database
Building custom renderers for other frameworks

Next steps

Adapters overview — submit to HTTP, Supabase, Postgres, webhooks
Schema anatomy — understand the full schema structure

Introduction→