JSON.fast
Schema-First API Development
Stop debugging API contracts and data transformations at runtime. JSON.fast validates schemas, transforms data structures, and generates type-safe code from specifications-catching errors at design time, not in production. Define your API once with JSON Schema or OpenAPI, automatically generate TypeScript types, validation logic, documentation, and test suites. Build robust APIs that never break compatibility.
The Problem We're Solving
Manual JSON management is error-prone
❌ The Old Way (Manual JSON)
- • API contracts documented in wikis, outdated instantly
- • Frontend and backend drift, runtime type errors in production
- • Manual validation code duplicated across services and languages
- • Data transformations scattered throughout codebase, impossible to audit
- • Breaking changes ship unknowingly, customers report bugs first
✅ The JSON.fast Way
- • Schema is source of truth-generate everything else from it
- • Type-safe code generated for TypeScript, Go, Rust, Python automatically
- • Validation logic created once, consistent across all services
- • Transform pipelines defined visually, applied consistently
- • Breaking changes detected in CI/CD before merge, never ship unknowingly
How It Works
Schema-first development workflow
Define Schema Once
Write JSON Schema or OpenAPI specification describing your data structures and API endpoints. Visual editor with autocomplete, examples, and instant validation. Support for complex types, inheritance, discriminators, and custom formats. Schema becomes single source of truth.
Generate Everything
Automatically create TypeScript interfaces, validation functions, API clients, mock servers, and documentation. Generate code for multiple languages from single schema. Update schema, regenerate-consistency guaranteed. No manual sync, no drift.
Validate & Transform
Runtime validation ensures data matches schema before processing. Transform pipelines convert between formats (JSON to XML, GraphQL, Protobuf). Migration tools help version APIs safely. Breaking change detection prevents incompatible updates.
Schema Superpowers
Everything you need for robust APIs
JSON Schema Validation
Validate JSON data against schemas with detailed error messages. Support for all JSON Schema draft versions (2019-09, 2020-12). Custom validation rules for business logic. Performance-optimized validators generated at build time, not runtime.
Data Transformation
Transform JSON structures with powerful mapping rules. Convert between formats, flatten nested objects, aggregate arrays. Visual transformation builder or write JSONata expressions. Test transformations with live preview. Chain transformations for complex pipelines.
Type Generation
Generate TypeScript, Go, Rust, Python, Java types from schemas. Full IDE autocomplete and type checking. Includes validation functions, serializers, deserializers. Keep frontend and backend types in perfect sync. Update once, types regenerate everywhere.
Auto Documentation
Beautiful API documentation generated from schemas automatically. Interactive examples, try-it-now console, code samples in multiple languages. Always up-to-date-docs regenerate with every schema change. Publish to public or private endpoints.
API Testing Suite
Generate comprehensive test suites from schemas. Unit tests for validators, integration tests for endpoints, contract tests between services. Mock servers with realistic data generation. Fuzzing to find edge cases. Tests fail when schemas change incompatibly.
Version Management
Track schema versions with semantic versioning. Detect breaking changes before merging PRs. Migration tools generate adapters between versions. Support multiple API versions simultaneously. Deprecation warnings for clients using old versions.
Standards & Tools
Built on proven specifications
JSON Schema
OpenAPI
Postman
TypeScript
Zod
Ajv
GraphQL
Swagger
Why Teams Choose JSON.fast
Schema-first API development wins
90% Fewer Runtime Errors
Catch type errors, validation failures, and contract mismatches at compile time instead of production. Schema validation prevents malformed data from entering your system. Type generation ensures frontend and backend always agree on data structures.
5x Faster API Development
Design API schema, generate client SDKs, server stubs, documentation, and tests automatically. No manual coding of serialization, validation, or transformation logic. Update schema, regenerate everything-changes propagate instantly across entire stack.
Perfect Frontend/Backend Sync
Single source of truth eliminates communication overhead. Frontend developers see type definitions and documentation before backend implementation exists. Mocked servers enable parallel development. Zero integration surprises.
Zero Breaking Changes
Automated breaking change detection in CI/CD prevents incompatible updates from merging. Semantic versioning tracks API evolution. Migration tools generate adapters between versions. Clients can opt into upgrades on their timeline. Backward compatibility guaranteed.
Real-World JSON Engineering
How teams build robust APIs
SaaS Platform API Design
B2B SaaS company with 50+ microservices needed consistent API contracts across teams. JSON.fast became central schema registry-teams designed APIs in OpenAPI, generated client SDKs for customers automatically. Breaking change detection prevented incompatible releases. Documentation updated automatically with every deployment. API versioning supported 5 versions simultaneously during major migration. Customer integration time dropped from weeks to hours with type-safe SDKs. Zero runtime contract violations after implementing schema validation at API gateway.
Legacy System Data Migration
Financial institution migrating from mainframe to cloud needed to transform decades of XML and CSV data to modern JSON APIs. JSON.fast transformation pipelines converted legacy formats, applied business rules, validated against new schemas. Processed 50TB of historical data with zero data loss. Generated migration reports showing schema compliance. Bidirectional transformations enabled gradual cutover-systems could read/write both formats. Audit trail tracked every transformation for regulatory compliance. Migration completed 6 months ahead of schedule.
Configuration Management at Scale
DevOps team managed configuration for 10K+ microservices across 50 environments. JSON.fast schemas defined config structure with validation rules. Generated TypeScript types meant services got compile-time config validation. Schema evolution tools migrated old configs to new versions automatically. Invalid configs rejected before deployment-no more production incidents from typos. Visual config editor with autocomplete reduced training time for new engineers. Centralized schema registry became documentation for all configuration options. Config validation prevented 200+ potential outages in first year.
Multi-Language SDK Generation
API-first startup needed SDKs for Python, Go, Ruby, and JavaScript to compete with established players. JSON.fast generated fully-typed SDKs in all 4 languages from single OpenAPI spec. Included validation, error handling, retry logic, rate limiting. SDKs published to package managers automatically on schema updates. Customers got instant SDK updates when new endpoints launched. Reduced SDK maintenance from 40 hours/week to zero. Expanded to 8 languages in year 2 with same automation. Developer satisfaction scores (from SDK users) increased 250%.
Contract Testing for Microservices
E-commerce platform with 200 microservices struggled with integration testing. JSON.fast contract tests validated that services honored schemas without spinning up dependencies. Consumer-driven contracts ensured providers didn't break clients unknowingly. Test generation from schemas meant 100% coverage with zero manual test writing. Mock servers with realistic data enabled isolated development. CI/CD pipeline failed builds that violated contracts-prevented deployment of breaking changes. Reduced integration bugs by 85%, eliminated entire QA testing phase. Teams deployed independently without fear of breaking others.
Real-Time Data Transformation Pipeline
Analytics platform ingested data from 1000+ external APIs with wildly different formats. JSON.fast transformations normalized data into canonical schemas. Visual transformation builder enabled non-technical analysts to map fields. Transformations executed at edge for minimal latency-processed 1M events/second. Schema validation caught malformed data before entering data warehouse. Transformation library grew to 5K+ reusable mappings. Added new data source in 30 minutes versus 2 weeks previously. Data quality improved from 60% to 99.9% clean records. Analysts spent time analyzing, not cleaning data.
JSON Schema Best Practices
Design robust, evolvable APIs
Start with Schema, Not Code
Design API contract before writing implementation. Schema-first approach surfaces design issues early. Enables parallel frontend/backend development. Generate code from schema, never the reverse. Schema is documentation and contract simultaneously.
Version Everything
Use semantic versioning for schemas-major.minor.patch. Major version for breaking changes, minor for additions, patch for fixes. Track schema evolution in version control. Support multiple versions simultaneously during migration periods. Deprecate gracefully with warnings.
Validate at Boundaries
Validate data when it enters your system-API gateway, event ingestion, file uploads. Reject invalid data immediately with clear error messages. Trust validated data internally-no redundant validation. Performance-optimize validators for hot paths. Log validation failures for monitoring.
Make Fields Optional by Default
Prefer optional fields with defaults over required fields. Easier to evolve APIs-adding required field is breaking change. Clients can omit fields they don't use. Use validation rules for business requirements, not schema structure. Enable backward and forward compatibility.
Use Composition for Reuse
Define reusable schema components with $ref, allOf, oneOf. Don't duplicate schema definitions. Create library of common types (User, Address, Timestamp). Composition enables consistent data modeling across APIs. Update shared types to fix issues everywhere simultaneously.
Test Schemas Thoroughly
Write test cases for valid and invalid data. Test edge cases-empty arrays, null values, huge strings. Ensure error messages are helpful. Validate schema compatibility in CI/CD before merging. Contract tests verify implementations match schemas. Fuzzing finds unexpected edge cases.
Design Better APIs Today
From runtime chaos to compile-time confidence
JSON.fast is part of the NextGen.fast ecosystem, bringing schema-first API development to teams worldwide. Design once, generate everything. Build APIs that never break.
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