# How form0 compares

<PageBadges />

import { Callout } from "zudoku/ui/Callout"

form0 is an open-source engine for schema-driven forms. It evaluates calculations, conditions,
validation, and events while leaving presentation, storage, and backend architecture under your
control. The projects below solve related problems at different layers, from embeddable form
libraries to complete data-collection platforms.

<Callout type="info" title="Last verified: September 29, 2026">
  Other projects change over time. Each statement about another project is based on its own
  documentation, listed under Sources at the end of this page. If something is out of date, use
  "Edit this page" to suggest a correction.
</Callout>

<Callout type="note" title="How to read the comparison">
  "Built in" means that the capability is part of the project's schema or runtime, without adding
  application code. ODK is a data-collection platform rather than an embeddable JavaScript library,
  so some comparisons describe a different architectural layer.
</Callout>

## At a glance

### Architecture and delivery

| Project                          | Runtime and UI model                                           | Documented targets                          | Backend and storage                                                     |
| -------------------------------- | -------------------------------------------------------------- | ------------------------------------------- | ----------------------------------------------------------------------- |
| **form0**                        | Framework-independent `form0-core`; UI bindings are separate   | React and React Native                      | Supplied by your application                                            |
| **SurveyJS**                     | Framework-independent `survey-core` with separate UI packages  | React, Angular, Vue 3, and plain JavaScript | Supplied by your application                                            |
| **Form.io**                      | Core and plain-JavaScript renderer, with framework wrappers    | Plain JavaScript, React, and Angular        | Can use application-owned storage or Form.io APIs and platform services |
| **ODK (XLSForm)**                | XLSForm definitions run as part of the ODK collection platform | ODK Collect for Android and ODK Web Forms   | ODK Central or another compatible server                                |
| **JSON Forms**                   | Framework-independent core with renderer sets                  | React, Angular, and Vue                     | Supplied by your application                                            |
| **react-jsonschema-form (RJSF)** | React form renderer driven by JSON Schema                      | React                                       | Supplied by your application                                            |

### Form logic

| Project           | Calculations and conditions                                                           | Repeating data                                                                    | Reaction model                                                |
| ----------------- | ------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------- | ------------------------------------------------------------- |
| **form0**         | JavaScript expressions for calculations, visibility, required, and read-only state    | Row-scoped logic; cross-row aggregation is not currently built in                 | `ON` handlers return operations for the host to apply         |
| **SurveyJS**      | SurveyJS expressions and calculated values                                            | Dynamic panels and matrices, including aggregate functions such as `sumInArray()` | Expressions and triggers can update the survey model          |
| **Form.io**       | JavaScript or JSON Logic calculations, conditions, and component logic                | Data Grid and Edit Grid; custom calculation code can inspect row data             | Logic triggers run actions on components or values            |
| **ODK (XLSForm)** | XPath-based calculations, relevance, constraints, and required expressions            | Repeats with XPath functions such as `sum()`                                      | Referenced values can trigger recalculation                   |
| **JSON Forms**    | JSON Schema validation and UI-schema rules; calculations require application code     | JSON Schema arrays; advanced aggregate logic requires application code            | UI rules react declaratively; `onChange` reports data changes |
| **RJSF**          | JSON Schema conditionals and dynamic UI schema; calculations require application code | JSON Schema arrays; advanced aggregate logic requires application code            | Application-level `onChange` callbacks                        |

### Licensing and visual authoring

| Project           | Open-source runtime                                                         | Visual authoring                                                                           |
| ----------------- | --------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------ |
| **form0**         | The engine, official bindings, CLI, and storage connectors are MIT-licensed | No drag-and-drop builder in form0; schemas can be authored directly or with CLI assistance |
| **SurveyJS**      | Form Library is MIT-licensed                                                | Survey Creator requires a commercial license                                               |
| **Form.io**       | `formio.js` and its included builder are MIT-licensed                       | Builder included in `formio.js`; additional platform products have separate licensing      |
| **ODK (XLSForm)** | ODK Collect is Apache-2.0 licensed                                          | Spreadsheet authoring with XLSForm and compatible tools                                    |
| **JSON Forms**    | MIT-licensed                                                                | No official visual builder                                                                 |
| **RJSF**          | Apache-2.0 licensed                                                         | No official visual builder                                                                 |

## Where form0 is different

### The same logic engine for web and native mobile

The React and React Native bindings both evaluate form logic through `form0-core`. A form definition
does not need a second calculation or condition system when an application moves between web and
native mobile, and React Native renders native controls rather than a web view. Presentation and
binding-specific lifecycle behavior can still differ between the two environments.

Among the projects above, ODK also provides a native Android runtime, but as part of the ODK
collection platform rather than as a React Native library for your application.

### Form behavior is separate from your application stack

form0 handles what a form is and how it behaves. Your application retains control of its design
system, navigation, authentication, API, storage, submission workflow, and hosting. This makes the
engine suitable for custom products that need sophisticated form behavior without adopting a
hosted form platform.

### Events describe changes instead of mutating implicitly

A form0 event handler returns operations such as `SETVALUE` or `ALERT`; it does not mutate form
state directly. A headless host can decide how to apply those operations, while the official
bindings apply the operations they support. The engine rejects any `SETVALUE` outside the handler's
scope, and applying an operation does not dispatch another `change` event, preventing event-handler
loops. See [Events and operations](/core/engine/events-operations).

SurveyJS triggers and Form.io logic actions, by comparison, update their form models directly.

### Plain field references, resolved by scope

In form0, an expression reads any field it is allowed to see with `$data_name`, whether the field
is in the main form or in the same repeating row. The engine resolves the reference from where the
expression is defined. SurveyJS uses prefixes such as `{panel.question}` and
`{parentPanel.question}` inside dynamic panels, Form.io distinguishes `data` from `row`, and XLSForm
uses XPath paths. See [Parent and child scopes](/core/engine/parent-child-scopes).

### Calculations ordered by dependency, with cycle diagnostics

form0 works out which calculated fields depend on which when the engine is created and evaluates
them in dependency order. If calculated fields depend on each other in a loop, the engine sets them
to `null`, reports a diagnostic that names the cycle, and continues evaluating independent fields.
See [Calculations and dependencies](/core/engine/calculations-dependencies).

### JavaScript expressions with validation controls

form0 expressions use JavaScript syntax, so developers do not need to learn a separate expression
language. `SAFE` and `CUSTOM` provide validation and configuration controls, but they are not
security sandboxes. Schemas containing expressions or event scripts must come from trusted authors;
applications must [isolate execution](/core/security) when schemas cannot be trusted. Form.io also
supports JavaScript and a protected evaluator, while SurveyJS and XLSForm use their own expression
languages.

### Open runtime and developer tooling

The engine, React and React Native bindings, CLI with AI-assisted authoring, and storage connectors
are MIT-licensed. You can build, preview, and run forms without depending on a commercial runtime.

## When another project may fit better

- **You need schema-defined aggregation across repeating rows today.** SurveyJS and ODK provide
  documented aggregate functions. Form.io can implement aggregation with custom calculation code.
  form0 does not currently provide a built-in cross-row aggregate.
- **You want visual authoring included with the library.** Form.io includes an open-source visual
  builder, while SurveyJS offers the commercial Survey Creator. form0 currently uses JSON schemas
  and CLI-assisted authoring. [reform](https://reformapp.io) is a separate hosted data-collection
  platform built on form0 and includes visual form authoring.
- **You need an established offline collection platform.** ODK and tools built on XLSForm have
  mature Android collection and spreadsheet-based authoring. form0 provides the engine and native
  binding; your application remains responsible for offline storage, synchronization, and backend
  operations.
- **Your application already uses JSON Schema as its form model.** JSON Forms and RJSF generate
  forms directly from JSON Schema and may require less translation into a separate form schema.

## Sources

- SurveyJS: [Architecture](https://surveyjs.io/documentation/surveyjs-architecture),
  [Form Library overview](https://surveyjs.io/form-library/documentation/overview),
  [licensing](https://surveyjs.io/licensing), and
  [conditional logic](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic)
- Form.io: [`formio.js`](https://github.com/formio/formio.js),
  [React integration](https://github.com/formio/react),
  [Angular integration](https://github.com/formio/angular),
  [JavaScript evaluator](https://help.form.io/dev/javascript-evaluator), and
  [logic and conditions](https://help.form.io/form-building/logic-and-conditions)
- ODK and XLSForm: [XLSForm](https://xlsform.org/en/),
  [ODK form logic](https://docs.getodk.org/form-logic/),
  [ODK Web Forms](https://docs.getodk.org/web-forms-intro/), and
  [ODK Collect](https://github.com/getodk/collect)
- JSON Forms: [Overview](https://jsonforms.io/),
  [renderer sets](https://jsonforms.io/docs/renderer-sets/),
  [UI-schema rules](https://jsonforms.io/docs/uischema/rules/), and
  [repository](https://github.com/eclipsesource/jsonforms)
- RJSF: [Documentation](https://rjsf-team.github.io/react-jsonschema-form/docs/),
  [array fields](https://rjsf-team.github.io/react-jsonschema-form/docs/json-schema/arrays/),
  [dynamic UI schema](https://rjsf-team.github.io/react-jsonschema-form/docs/api-reference/dynamic-ui-schema-examples/),
  and [`Form` callbacks](https://rjsf-team.github.io/react-jsonschema-form/docs/api-reference/form-props/)