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How form0 compares

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.

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.

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.

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.

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 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 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, Form Library overview, licensing, and conditional logic
• Form.io: formio.js, React integration, Angular integration, JavaScript evaluator, and logic and conditions
• ODK and XLSForm: XLSForm, ODK form logic, ODK Web Forms, and ODK Collect
• JSON Forms: Overview, renderer sets, UI-schema rules, and repository
• RJSF: Documentation, array fields, dynamic UI schema, and Form callbacks