Open-source alternatives to Marshmallow

Vee-validate is a form validation library and state management tool for Vue applications. It enables the validation of user inputs through declarative rules and tracks form metadata, including submission status and dirty states. The library functions as a wrapper for integrating external schema validation libraries to enforce consistent data shapes. It also serves as an internationalized framework for displaying translated error messages and localized feedback. The project covers broad capability areas including form state management, the handling of complex nested data structures, and the s

JSONModel is a data modeling framework and serialization library for Apple platforms, including iOS, macOS, watchOS, and tvOS. It transforms JSON strings and dictionaries into typed Swift objects to eliminate manual dictionary parsing. The framework provides a mapping system that utilizes custom key rules and dot-notation to resolve nested data hierarchies. It supports the conversion of complex JSON structures into organized model relationships and manages the transformation of JSON arrays into collections of typed model instances. The toolset includes data type transformation via custom tra

Instructor is a framework designed for structured data extraction, validation, and language model integration. It functions as a library that transforms unstructured text into validated, type-safe objects by leveraging schema definitions and model-specific tool-calling capabilities. By acting as a validation middleware, the project ensures that language model outputs strictly conform to defined data structures. The library distinguishes itself through a robust validation-based retry loop that automatically re-submits failed responses with error feedback to iteratively correct schema complianc

electron-store is a persistence layer and key-value storage solution for Electron applications. It manages user preferences and application state by saving and retrieving structured data as JSON files on the local file system. The library includes capabilities for obfuscating configuration files to prevent manual modification of saved data. It also provides a system for automatic data structure migration when the application version is incremented and supports custom serialization pipelines to replace standard JSON parsing. The project covers a broad surface of state management, including sc

This project is a Protocol Buffers implementation for Go, providing a binary serialization framework to convert native data structures into a compact binary format for efficient network transmission and storage. It functions as a language bindings generator, utilizing a compiler plugin to create Go source code from platform-neutral protocol buffer definitions. The implementation includes a JSON data mapper that transforms structured binary messages into JSON format to facilitate compatibility with web services and external APIs. It also enables cross-language data exchange by using a common s

Protocol Buffers is a language-neutral, platform-agnostic mechanism for serializing structured data. It provides a schema-driven toolchain that compiles declarative data definitions into type-safe source code, enabling consistent communication and strongly typed API contracts across services written in different programming languages. The project distinguishes itself through a highly efficient binary wire format that utilizes tag-based encoding and variable-width integer compression to minimize payload size and processing overhead. It supports robust evolutionary schema management, allowing d

FlatBuffers is a cross-platform serialization library designed for performance-critical applications that require efficient, zero-copy data access. By organizing data in a structured binary format, it allows applications to read and write complex data structures directly from memory-mapped buffers without the need for intermediate parsing or temporary object allocation. The project distinguishes itself through a schema-driven approach that balances high-performance access with long-term data evolution. It utilizes a unique memory layout featuring relative offsets and inline fixed-size structu

Bond was a cross-platform framework for working with schematized data. The open-source project ended on March 31, 2025.

Colfer is a binary serialization format optimized for speed and size.

This project is a Protocol Buffers Go compiler and code generation framework that translates schema definitions into optimized Go structures and reflection-free serialization methods. It includes a gRPC service generator for producing client and server communication code and a serialization performance toolkit for generating automated benchmarks and test suites. The framework features a plugin-based system for transforming data definitions into source code with custom field mapping and struct tag injection. It allows for custom type mapping and struct type overriding to link data fields to sp

Python wrapper around rapidjson

mapstructure is a reflection-based library for the bidirectional encoding and decoding of generic map data into native typed Go structures. It functions as a tool for transforming loosely typed map values into specific structs and encoding those structs back into maps. The library utilizes Go reflection to map generic data keys to struct fields during runtime. It supports the transformation of untyped data from dynamic sources or configuration files into type-safe native structures. The mapping process includes recursive traversal of nested maps and slices, as well as the use of struct tags

idiomatic codec and rpc lib for msgpack, cbor, json, etc. msgpack.orgGo

This project is a high-performance JSON library for Go, serving as a replacement for the standard encoding/json package. It provides a serialization engine for encoding and decoding data structures, alongside a schemaless parser for extracting specific values from JSON blobs using paths. The library distinguishes itself through a focus on reducing CPU and memory overhead. It implements a high-performance encoder that utilizes buffer reuse and reduced float precision to increase data throughput. Broad capability areas include data serialization, high-performance JSON processing, and schema-le

csvutil provides fast and idiomatic mapping between CSV and Go (golang) values.

TanStack Form is a cross-framework form state management library that provides typed fields, validation, and submission across React, Vue, Angular, Solid, Lit, Svelte, and Preact. It uses a shared form model that adapts to different UI frameworks while preserving the same validation and submission logic, and offers headless form controls that impose no UI markup, letting developers bring their own inputs and design system. The library distinguishes itself through granular state subscription, where components subscribe to narrow slices of form or field state using reactive primitives, so only

Joi is a JavaScript data validation library used to define schemas that ensure the structure and data types of objects remain consistent. It functions as a schema-based validator and object schema definition tool, preventing invalid information from entering an application by checking data against predefined constraints and rules. The library employs a chainable fluent interface and a constraint-based validation engine to build complex validation pipelines. It utilizes recursive tree traversal to validate nested data structures and a type-coercion pipeline to transform input values into the t

Valibot is a modular, type-safe schema library for validating and parsing structural data in TypeScript environments.

ObjectMapper is a JSON serialization framework for Swift that maps JSON strings and dictionaries into strongly typed classes and structs. It functions as a data mapper and converter, facilitating the bidirectional transformation of data between raw JSON and Swift model objects. The library uses protocol-based mapping to associate specific JSON keys with object properties. It supports nested key extraction via dot-notation pathing and employs custom transformation classes to bridge the gap between JSON and Swift types. The framework provides capabilities for model validation during initializa

Joi is a JavaScript data validation library used to define schemas that validate, cast, and sanitize data objects. It functions as an object schema validator and parser, ensuring that input data matches specific types and formats before it is processed by an application. The library features a conditional validation engine capable of dynamic schema enforcement, where validation logic and dependencies change based on the values of other keys within an object. It also serves as a data casting and sanitization tool, transforming input values into target types and removing sensitive keys from the