pedantigo

README

Pedantigo

Type-safe JSON validation and schema generation for Go.

v2 breaking change: the default struct tag changed from pedantigo to validate. This is to be in sync with wider range of community tools like swaggo that work with validate tags If you're upgrading from v1, see the migration guide before you update.

New projects should start with v2. v1 is maintained only for existing users — it receives no new features. All new feature development happens in v2.

Installation

go get github.com/SmrutAI/pedantigo/v2/validator

Requires Go 1.21+ (nuances)

Quick Example

type User struct {
    Email string `json:"email" validate:"required,email"`
    Age   int    `json:"age" validate:"min=18"`
}

// Parse and validate JSON
user, err := vl.Unmarshal[User](jsonData)
if err != nil {
    // Handle validation errors with field paths and error codes
    if ve, ok := err.(*validator.ValidationError); ok {
        for _, fe := range ve.Errors {
            fmt.Printf("%s: %s\n", fe.Field, fe.Message)
        }
    }
}

// Generate JSON Schema for LLM tools (no $schema field)
schemaBytes, _ := validator.SchemaJSONLLM[User]()

Framework Plugins

Plugins wire pedantigo directly into a web framework's own request-binding step, so validation runs automatically instead of requiring manual io.ReadAll + Unmarshal calls in every handler. Echo replaces the binder directly; Gin installs into both its JSON codec and validation hooks.

import "github.com/SmrutAI/pedantigo/plugins/web/pedantigoecho/v2"

e := echo.New()
e.Binder = pedantigoecho.NewBinder()

Features

Feature	Description
100+ Constraints	Email, URL, UUID, regex, numeric ranges, string length, and more
JSON Schema Generation	Auto-generate schemas for LLM tool calling and OpenAPI
240x Caching Speedup	Schema generation cached for high performance
Streaming Validation	Validate partial JSON from LLM streams
Discriminated Unions	Type-safe polymorphic data handling
Cross-Field Validation	Validate relationships between fields
Zero Dependencies	Only invopop/jsonschema + Go stdlib

Plugins

Plugin	Framework	Description
Echo Binder	Echo	Drop-in echo.Binder — automatic validation on every c.Bind() call
Gin Request Plugin	Gin	Installs Pedantigo into codec/json.API + binding.Validator for automatic request binding validation

Documentation

Full documentation at pedantigo.dev

• Getting Started - Installation and first steps
• Validation Concepts - How validation works
• JSON Schema Generation - Generate schemas for LLM tools
• Constraint Reference - All 100+ validation rules
• Streaming Validation - Handle LLM streaming responses
• API Reference - Complete API documentation
• Benchmarks - Performance comparisons with other validation libraries

Use Cases

Use Case	Why Pedantigo?
API Request Validation	Validate incoming JSON, return structured errors
LLM Structured Output	Generate JSON Schema for function calling, validate responses
Configuration Files	Parse config with defaults, fail fast on invalid values
Data Pipeline Input	Ensure data quality at ingestion with detailed error paths

Feature Coverage

See API_PARITY.md for detailed comparison with Pydantic v2 and go-playground/validator.

License

MIT