Version: 1.1.2

JSON Schema Generation

Automatically generate JSON Schemas from your Go structs. Pedantigo schemas map validation constraints to standard JSON Schema keywords for API documentation, form generation, LLM structured output, and more.

Quick Start

Get a JSON Schema with a single function call:

package main

import (
    "fmt"
    "encoding/json"
    "github.com/smrutai/pedantigo"
)

type User struct {
    Name  string `json:"name" pedantigo:"required,min=2,max=50"`
    Email string `json:"email" pedantigo:"required,email"`
    Age   int    `json:"age" pedantigo:"min=18,max=120"`
}

func main() {
    // Get schema as object
    schema := pedantigo.Schema[User]()

    // Get schema as JSON bytes
    schemaBytes, _ := pedantigo.SchemaJSON[User]()
    fmt.Println(string(schemaBytes))
}

Output:

{
  "title": "User",
  "type": "object",
  "properties": {
    "name": {
      "type": "string",
      "minLength": 2,
      "maxLength": 50
    },
    "email": {
      "type": "string",
      "format": "email"
    },
    "age": {
      "type": "integer",
      "minimum": 18,
      "maximum": 120
    }
  },
  "required": ["name", "email", "age"]
}

LLM Tool Calling Compatibility

Pedantigo's default Schema() and SchemaJSON() produce flattened schemas optimized for LLM tool calling APIs.

Schema Output Comparison

Function	`$ref/$defs`	Best For
`Schema()` / `SchemaJSON()`	No - all types expanded inline	LLM tool calling (OpenAI, Anthropic, Gemini)
`SchemaOpenAPI()` / `SchemaJSONOpenAPI()`	Yes - uses references	OpenAPI specs, Swagger docs

Example: Flattened Schema Output

type Address struct {
    Street string `json:"street" pedantigo:"required"`
    City   string `json:"city" pedantigo:"required"`
}

type User struct {
    Name    string  `json:"name" pedantigo:"required"`
    Address Address `json:"address"`
}

schemaBytes, _ := pedantigo.SchemaJSON[User]()

Output (flattened - ready for LLM tools):

{
  "type": "object",
  "properties": {
    "name": {"type": "string"},
    "address": {
      "type": "object",
      "properties": {
        "street": {"type": "string"},
        "city": {"type": "string"}
      },
      "required": ["street", "city"]
    }
  },
  "required": ["name"]
}

No $ref or $defs - the schema works directly with OpenAI, Anthropic, and Gemini function calling APIs.

tip

For LLM integrations, see Streaming Validation for handling streaming responses, and LLM Streaming Examples for complete integration patterns.

Simple API Functions

Schema()

Get the JSON Schema as a jsonschema.Schema object.

func Schema[T any]() *jsonschema.Schema

Returns: A *jsonschema.Schema object from the invopop/jsonschema package.

Cached: First call generates schema (~10ms), subsequent calls return cached result (sub-100ns).

Example:

schema := pedantigo.Schema[User]()
fmt.Println("Title:", schema.Title)
fmt.Println("Required fields:", schema.Required)
fmt.Println("Properties:", schema.Properties)

SchemaJSON()

Get the JSON Schema as JSON bytes.

func SchemaJSON[T any]() ([]byte, error)

Returns: JSON bytes, or error if serialization fails.

Use cases:

Write schema to file
Return schema in HTTP response
Send to frontend for form generation
Store in database

Example:

schemaBytes, err := pedantigo.SchemaJSON[User]()
if err != nil {
    log.Fatal(err)
}

// Write to file
os.WriteFile("user-schema.json", schemaBytes, 0644)

// Return in HTTP response
w.Header().Set("Content-Type", "application/json")
w.Write(schemaBytes)

SchemaOpenAPI()

Get an OpenAPI 3.1 compatible component schema.

func SchemaOpenAPI[T any]() *jsonschema.Schema

Returns: A JSON Schema compatible with OpenAPI 3.1 specifications.

Important: This generates a component schema (for use in components/schemas), not a complete OpenAPI document. Pedantigo is a validation library, not an API framework like Huma. For benchmarks, we only measure component schema generation performance.

Features:

Support for nullable fields (pointer types)
Compatible with OpenAPI 3.1 specifications (uses $defs syntax)
Uses $ref and $defs for better composition

Example:

type APIResponse struct {
    Success bool   `json:"success" pedantigo:"required"`
    Data    *User  `json:"data"`        // nullable
    Message string `json:"message,omitempty"`
}

schema := pedantigo.SchemaOpenAPI[APIResponse]()
// Use in OpenAPI spec

SchemaJSONOpenAPI()

Get OpenAPI-compatible schema as JSON bytes.

func SchemaJSONOpenAPI[T any]() ([]byte, error)

Returns: JSON bytes with OpenAPI enhancements.

Example:

schemaBytes, err := pedantigo.SchemaJSONOpenAPI[APIResponse]()
if err != nil {
    log.Fatal(err)
}

// Embed in OpenAPI YAML/JSON specification

Performance & Caching

Pedantigo schemas are automatically cached with a 240x speedup:

Operation	Time	Details
First call (any type)	~10ms	Includes reflection and generation
Cached calls	~100ns	240x faster
Memory overhead	Minimal	Per-type cache with type hash validation

How it works:

First call: Type is reflected, constraints parsed, schema generated
Cached calls: Previous result returned instantly
Thread-safe: sync.Map ensures only one schema per type
Invalidation: Type hash detects if struct changes between calls

Benchmark example:

// First call: ~10ms
schema1 := pedantigo.Schema[User]()

// Subsequent calls: <100ns (nearly free)
for i := 0; i < 1000000; i++ {
    schema := pedantigo.Schema[User]()
}

// Different types get separate caches
schemaUser := pedantigo.Schema[User]()      // ~10ms
schemaProduct := pedantigo.Schema[Product]() // ~10ms
schemaOrder := pedantigo.Schema[Order]()    // ~10ms

Constraint Mapping

Pedantigo validation constraints are automatically mapped to JSON Schema keywords. This means your validation rules are instantly documented in the generated schema.

Core Constraints

Constraint	JSON Schema	Description	Example
`required`	`required: [...]`	Field is required	`pedantigo:"required"`
`min`	`minimum` / `minLength`	Numeric min or string length	`pedantigo:"min=18"`
`max`	`maximum` / `maxLength`	Numeric max or string length	`pedantigo:"max=100"`
`gt`	`exclusiveMinimum`	Greater than (numeric)	`pedantigo:"gt=0"`
`gte`	`minimum`	Greater than or equal	`pedantigo:"gte=1"`
`lt`	`exclusiveMaximum`	Less than (numeric)	`pedantigo:"lt=100"`
`lte`	`maximum`	Less than or equal	`pedantigo:"lte=99"`
`len`	`minLength=X, maxLength=X`	Exact string/array length	`pedantigo:"len=32"`
`oneof` / `enum`	`enum: [...]`	Must be one of values	`pedantigo:"oneof=draft published archived"`

String Constraints

Constraint	JSON Schema	Example
`minLength`	`minLength`	`pedantigo:"minLength=3"`
`maxLength`	`maxLength`	`pedantigo:"maxLength=255"`
`pattern`	`pattern`	`pedantigo:"pattern=^[a-z]+$"`
`email`	`format: "email"`	`pedantigo:"email"`
`url`	`format: "uri"`	`pedantigo:"url"`
`uuid`	`format: "uuid"`	`pedantigo:"uuid"`
`lowercase`	`pattern` (enforced)	`pedantigo:"lowercase"`
`uppercase`	`pattern` (enforced)	`pedantigo:"uppercase"`

Numeric Constraints

Constraint	JSON Schema	Example
`positive`	`exclusiveMinimum: 0`	`pedantigo:"positive"`
`negative`	`exclusiveMaximum: 0`	`pedantigo:"negative"`
`multiple_of`	`multipleOf`	`pedantigo:"multiple_of=5"`
`decimal_places`	Custom format	`pedantigo:"decimal_places=2"`

Format Constraints

All standard formats map to format keyword:

Constraint	Format Value	Example
`email`	`"email"`	`pedantigo:"email"`
`ipv4`	`"ipv4"`	`pedantigo:"ipv4"`
`ipv6`	`"ipv6"`	`pedantigo:"ipv6"`
`hostname`	`"hostname"`	`pedantigo:"hostname"`
`fqdn`	`"fqdn"`	`pedantigo:"fqdn"`
`port`	`"port"`	`pedantigo:"port"`
`jwt`	`"jwt"`	`pedantigo:"jwt"`
`semver`	`"semver"`	`pedantigo:"semver"`

Collection Constraints

Constraint	JSON Schema	Example
`minItems`	`minItems`	`pedantigo:"minItems=1"`
`maxItems`	`maxItems`	`pedantigo:"maxItems=100"`
`unique`	`uniqueItems: true`	`pedantigo:"unique"`

Schema Metadata Tags

Control schema generation with metadata tags in the pedantigo struct tag:

Title

Set the schema title for a field:

type User struct {
    Name string `json:"name" pedantigo:"required,title=Full Name"`
}

Generated schema:

{
  "type": "object",
  "properties": {
    "name": {
      "title": "Full Name",
      "type": "string"
    }
  }
}

Description

Add field description (appears in API docs, forms, etc.):

type User struct {
    Email string `json:"email" pedantigo:"required,email,description=User's primary email address"`
    Age   int    `json:"age" pedantigo:"min=0,max=150,description=Age in years (0-150)"`
}

Generated schema:

{
  "properties": {
    "email": {
      "type": "string",
      "description": "User's primary email address",
      "format": "email"
    },
    "age": {
      "type": "integer",
      "description": "Age in years (0-150)",
      "minimum": 0,
      "maximum": 150
    }
  }
}

Examples

Provide example values in the schema:

type Product struct {
    Name     string  `json:"name" pedantigo:"required,examples=Laptop|Monitor|Keyboard"`
    Price    float64 `json:"price" pedantigo:"gt=0,examples=99.99|299.99|1999.99"`
    Discount float64 `json:"discount" pedantigo:"min=0,max=100,examples=10|25|50"`
}

Syntax: Pipe-separated values examples=value1|value2|value3

Generated schema:

{
  "properties": {
    "name": {
      "type": "string",
      "examples": ["Laptop", "Monitor", "Keyboard"]
    },
    "price": {
      "type": "number",
      "examples": [99.99, 299.99, 1999.99],
      "exclusiveMinimum": 0
    }
  }
}

Deprecated

Mark fields as deprecated:

type User struct {
    Name     string `json:"name" pedantigo:"required"`
    OldEmail string `json:"old_email" pedantigo:"email,deprecated"`
    // or with message:
    LegacyID int `json:"legacy_id" pedantigo:"deprecated=Use 'id' field instead"`
}

Generated schema:

{
  "properties": {
    "old_email": {
      "type": "string",
      "deprecated": true,
      "description": "This field is deprecated"
    },
    "legacy_id": {
      "type": "integer",
      "deprecated": true,
      "description": "Use 'id' field instead"
    }
  }
}

Complete Schema Example

Here's a realistic example showing constraint mapping and metadata:

package main

import (
    "fmt"
    "github.com/smrutai/pedantigo"
)

type CreateUserRequest struct {
    // Basic fields with constraints
    Name string `json:"name" pedantigo:"required,min=2,max=100,title=Full Name,description=User's full name"`

    // Email with format constraint
    Email string `json:"email" pedantigo:"required,email,description=Primary email address"`

    // Numeric with range
    Age int `json:"age" pedantigo:"min=18,max=120,description=Age in years"`

    // Enum field
    Status string `json:"status" pedantigo:"required,oneof=active inactive suspended,description=Account status"`

    // Optional field with description
    Bio string `json:"bio,omitempty" pedantigo:"maxLength=500,description=User biography"`

    // Tags/roles array
    Tags []string `json:"tags,omitempty" pedantigo:"maxItems=10,unique,description=User interests and skills"`

    // URL field
    Website string `json:"website,omitempty" pedantigo:"url,description=User's personal website"`

    // Deprecated field
    OldUsername string `json:"old_username,omitempty" pedantigo:"deprecated=Use 'name' instead"`
}

func main() {
    schema := pedantigo.Schema[CreateUserRequest]()

    // Use the schema for API documentation
    fmt.Printf("Title: %s\n", schema.Title)
    fmt.Printf("Required: %v\n", schema.Required)

    // Get as JSON
    schemaJSON, _ := pedantigo.SchemaJSON[CreateUserRequest]()
    fmt.Println(string(schemaJSON))
}

Generated JSON:

{
  "type": "object",
  "title": "CreateUserRequest",
  "properties": {
    "name": {
      "type": "string",
      "title": "Full Name",
      "description": "User's full name",
      "minLength": 2,
      "maxLength": 100
    },
    "email": {
      "type": "string",
      "description": "Primary email address",
      "format": "email"
    },
    "age": {
      "type": "integer",
      "description": "Age in years",
      "minimum": 18,
      "maximum": 120
    },
    "status": {
      "type": "string",
      "description": "Account status",
      "enum": ["active", "inactive", "suspended"]
    },
    "bio": {
      "type": "string",
      "description": "User biography",
      "maxLength": 500
    },
    "tags": {
      "type": "array",
      "description": "User interests and skills",
      "items": { "type": "string" },
      "maxItems": 10,
      "uniqueItems": true
    },
    "website": {
      "type": "string",
      "description": "User's personal website",
      "format": "uri"
    },
    "old_username": {
      "type": "string",
      "deprecated": true,
      "description": "Use 'name' instead"
    }
  },
  "required": ["name", "email", "age", "status"]
}

Nested Structs

Nested structs are automatically inlined in the default schema mode:

type Address struct {
    Street string `json:"street" pedantigo:"required"`
    City   string `json:"city" pedantigo:"required"`
    Zip    string `json:"zip" pedantigo:"required,len=5"`
}

type User struct {
    Name    string  `json:"name" pedantigo:"required"`
    Address Address `json:"address" pedantigo:"required"`
}

schema := pedantigo.Schema[User]()

Generated schema (inlined):

{
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "address": {
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "city": { "type": "string" },
        "zip": {
          "type": "string",
          "minLength": 5,
          "maxLength": 5
        }
      },
      "required": ["street", "city", "zip"]
    }
  },
  "required": ["name", "address"]
}

For OpenAPI-style composition using $ref and $defs, use SchemaOpenAPI() instead.

Use Cases

API Documentation

Generate OpenAPI/Swagger specs automatically:

type CreatePostRequest struct {
    Title   string `json:"title" pedantigo:"required,min=5,max=200,description=Post title"`
    Content string `json:"content" pedantigo:"required,min=10,max=10000,description=Post content"`
    Tags    []string `json:"tags" pedantigo:"maxItems=10,unique,description=Post tags"`
}

schema := pedantigo.SchemaJSONOpenAPI[CreatePostRequest]()
// Include in OpenAPI spec components/schemas

Frontend Form Generation

Send schema to frontend for dynamic form building:

// HTTP handler
func handleGetSchema(w http.ResponseWriter, r *http.Request) {
    schemaBytes, _ := pedantigo.SchemaJSON[CreatePostRequest]()

    w.Header().Set("Content-Type", "application/json")
    w.Write(schemaBytes)
}

// Frontend receives schema and generates form fields dynamically

LLM Structured Output

Provide schema to LLMs for structured generation:

type TranslationResult struct {
    Original string `json:"original" pedantigo:"required,description=Original text"`
    Translated string `json:"translated" pedantigo:"required,description=Translated text"`
    Language string `json:"language" pedantigo:"required,oneof=en es fr de,description=Target language code"`
    Confidence float64 `json:"confidence" pedantigo:"min=0,max=1,description=Translation confidence 0-1"`
}

schema := pedantigo.SchemaJSON[TranslationResult]()
// Pass to Claude, GPT, etc. for structured generation

Database Schema Generation

Use generated schema to validate before persisting:

// Unmarshal validates against constraints
user, err := pedantigo.Unmarshal[User](jsonData)
if err != nil {
    return err // All validation done before database
}

// user is guaranteed valid
db.Insert(user)

Runtime Type Inspection

Query the schema at runtime:

schema := pedantigo.Schema[User]()

// Check which fields are required
requiredFields := schema.Required
fmt.Printf("Required fields: %v\n", requiredFields)

// Get property details
if emailProp, ok := schema.Properties["email"]; ok {
    fmt.Printf("Email format: %s\n", emailProp.Format)
}

Performance Characteristics

Schema generation is optimized for speed:

Operation	Time	Notes
First schema call	~10ms	Reflection + generation + caching
Cached schema call	~100ns	240x faster
Serializing to JSON	~1ms	Efficient JSON marshaling
Retrieving from cache	~100ns	`sync.Map` lookup

The 240x speedup means you can safely call Schema[T]() in hot paths after the first call.

Comparison with Validation

Schema describes what is valid (documentation). Validation checks if data is valid (enforcement).

Both use the same constraints, so they're always in sync:

// These use the same constraint definitions:
schema := pedantigo.Schema[User]()           // For documentation
user, err := pedantigo.Unmarshal[User](data) // For validation

No manual schema maintenance needed - change a constraint, both schema and validation update automatically.

Limitations & Notes

Embedded types: Not supported in constraints (design choice for simplicity)
Custom types: Custom constraint types are included in schema but may need custom validator implementation
Nullable fields: Use *T (pointer) to make a field optional
Schema references: $ref only used in OpenAPI mode (SchemaOpenAPI), default mode inlines

Next Steps

See Validation Basics for validation constraints
Learn Constraints Reference for complete constraint list
Check Examples for real-world usage patterns

Quick Start​

LLM Tool Calling Compatibility​

Schema Output Comparison​

Example: Flattened Schema Output​

Simple API Functions​

Schema()​

SchemaJSON()​

SchemaOpenAPI()​

SchemaJSONOpenAPI()​

Performance & Caching​

Constraint Mapping​

Core Constraints​

String Constraints​

Numeric Constraints​

Format Constraints​

Collection Constraints​

Schema Metadata Tags​

Title​

Description​

Examples​

Deprecated​

Complete Schema Example​

Nested Structs​

Use Cases​

API Documentation​

Frontend Form Generation​

LLM Structured Output​

Database Schema Generation​

Runtime Type Inspection​

Performance Characteristics​

Comparison with Validation​

Limitations & Notes​

Next Steps​

Quick Start

LLM Tool Calling Compatibility

Schema Output Comparison

Example: Flattened Schema Output

Simple API Functions

Schema()

SchemaJSON()

SchemaOpenAPI()

SchemaJSONOpenAPI()

Performance & Caching

Constraint Mapping

Core Constraints

String Constraints

Numeric Constraints

Format Constraints

Collection Constraints

Schema Metadata Tags

Title

Description

Examples

Deprecated

Complete Schema Example

Nested Structs

Use Cases

API Documentation

Frontend Form Generation

LLM Structured Output

Database Schema Generation

Runtime Type Inspection

Performance Characteristics

Comparison with Validation

Limitations & Notes

Next Steps