valai

AI-native TypeScript validation library optimized for LLM outputs, function calling, and structured generation.

import { v } from 'valai';

const ProductSchema = v.object({
  name: v.string().describe('Product name'),
  price: v.number().min(0),
  category: v.enum(['electronics', 'clothing', 'food']),
  inStock: v.boolean().default(true)
});

// Parse messy LLM output with auto-repair
const result = ProductSchema.parseLLM(`
  \`\`\`json
  {
    name: 'iPhone 15',    // unquoted key, single quotes
    price: 999,           // trailing comma
  }
  \`\`\`
`);

// Export for OpenAI function calling
const tool = ProductSchema.toOpenAI({ name: 'extract_product' });

Features

• LLM-First Design - Built specifically for validating AI/LLM outputs
• Auto JSON Repair - Fixes trailing commas, single quotes, unquoted keys, comments, and more
• Markdown Extraction - Automatically extracts JSON from code blocks
• Type Coercion - Smart coercion in LLM mode ("25" → 25)
• Multi-Format Export - JSON Schema, OpenAI, Claude, and Gemini formats
• AI Metadata - .describe() and .examples() for better LLM guidance
• Partial Data on Failure - Get what was parsed for retry scenarios
• Full TypeScript Support - Complete type inference like Zod

Installation

npm install valai

Quick Start

Basic Validation

import { v } from 'valai';

// Define a schema
const UserSchema = v.object({
  name: v.string().min(1),
  email: v.string().email(),
  age: v.number().int().min(0).optional()
});

// Infer TypeScript type
type User = v.infer<typeof UserSchema>;
// { name: string; email: string; age?: number }

// Strict parsing (throws on error)
const user = UserSchema.parse({ name: 'John', email: 'john@example.com' });

// Safe parsing (returns result object)
const result = UserSchema.safeParse(data);
if (result.success) {
  console.log(result.data);
} else {
  console.log(result.error.issues);
}

LLM Output Parsing

// parseLLM() handles common LLM output issues:
const schema = v.object({
  name: v.string(),
  score: v.number()
});

// Handles: markdown code blocks, single quotes, unquoted keys,
// trailing commas, comments, and type coercion
const result = schema.parseLLM(`
Here's the extracted data:
\`\`\`json
{
  name: 'Test',     // unquoted key + single quotes
  score: "95",      // string that should be number
}
\`\`\`
`);

console.log(result.data); // { name: 'Test', score: 95 }

AI-Optimized Schemas

const ProductSchema = v.object({
  name: v.string()
    .describe('The product name as it appears on the packaging')
    .examples(['iPhone 15 Pro', 'MacBook Air M3']),

  price: v.number()
    .min(0)
    .describe('Price in USD'),

  category: v.enum(['electronics', 'clothing', 'food', 'other'])
    .describe('Primary product category')
});

// Descriptions and examples are included in exported schemas
const jsonSchema = ProductSchema.toJSONSchema();

Export for LLM APIs

// OpenAI Function Calling
const openAITool = schema.toOpenAI({
  name: 'extract_product',
  description: 'Extract product information from text'
});

// Anthropic/Claude Tools
const claudeTool = schema.toClaude({
  name: 'extract_product',
  description: 'Extract product information from text'
});

// Google Gemini
const geminiFunc = schema.toGemini({
  name: 'extract_product',
  description: 'Extract product information from text'
});

// Standard JSON Schema (2020-12)
const jsonSchema = schema.toJSONSchema();

Schema Types

Primitives

v.string()    // string
v.number()    // number
v.boolean()   // boolean
v.null()      // null
v.undefined() // undefined
v.any()       // any
v.unknown()   // unknown

String Validations

v.string()
  .min(1)              // Minimum length
  .max(100)            // Maximum length
  .length(10)          // Exact length
  .email()             // Email format
  .url()               // URL format
  .uuid()              // UUID format
  .regex(/pattern/)    // Custom regex
  .includes('text')    // Contains substring
  .startsWith('pre')   // Starts with
  .endsWith('suf')     // Ends with
  .trim()              // Trim whitespace (transform)
  .toLowerCase()       // To lowercase (transform)
  .toUpperCase()       // To uppercase (transform)

Number Validations

v.number()
  .min(0)              // Minimum (inclusive)
  .max(100)            // Maximum (inclusive)
  .gt(0)               // Greater than
  .lt(100)             // Less than
  .int()               // Integer only
  .positive()          // > 0
  .negative()          // < 0
  .nonnegative()       // >= 0
  .nonpositive()       // <= 0
  .multipleOf(5)       // Multiple of
  .finite()            // No Infinity

Objects

const schema = v.object({
  name: v.string(),
  age: v.number().optional()
});

// Object methods
schema.extend({ email: v.string() })  // Add properties
schema.merge(otherSchema)             // Merge schemas
schema.pick({ name: true })           // Pick properties
schema.omit({ age: true })            // Omit properties
schema.partial()                      // All optional
schema.required()                     // All required
schema.strict()                       // Error on extra keys
schema.passthrough()                  // Keep extra keys
schema.strip()                        // Remove extra keys (default)

Arrays

v.array(v.string())           // string[]
  .min(1)                     // Minimum length
  .max(10)                    // Maximum length
  .length(5)                  // Exact length
  .nonempty()                 // At least 1 element

Tuples

v.tuple([v.string(), v.number()])     // [string, number]
v.tuple([v.string()]).rest(v.number()) // [string, ...number[]]

Unions & Enums

// String enum
v.enum(['pending', 'active', 'completed'])

// Native TypeScript enum
enum Status { Pending, Active }
v.nativeEnum(Status)

// Union types
v.union([v.string(), v.number()])     // string | number

// Discriminated union
v.discriminatedUnion('type', [
  v.object({ type: v.literal('a'), value: v.string() }),
  v.object({ type: v.literal('b'), count: v.number() })
])

// Literal
v.literal('active')                    // 'active'

Records

v.record(v.number())                   // Record<string, number>
v.record(v.string().uuid(), v.any())   // Record with UUID keys

Modifiers

v.string().optional()           // string | undefined
v.string().nullable()           // string | null
v.string().default('anonymous') // Default value if undefined

JSON Repair

valai includes powerful JSON repair utilities for handling malformed LLM outputs:

import { repairJSON, parseAndRepair, isValidJSON } from 'valai';

// Full repair with detailed result
const result = repairJSON(`{
  name: 'test',     // unquoted key, single quotes
  value: 123,       // trailing comma
}`);

console.log(result.success);  // true
console.log(result.data);     // { name: 'test', value: 123 }
console.log(result.repairs);  // List of repairs made

// Parse and repair in one step
const data = parseAndRepair('{"a": 1,}');

// Check if valid JSON
isValidJSON('{"a": 1}');  // true
isValidJSON('{a: 1}');    // false

Repair Capabilities

Issue	Example	Fixed
Markdown code blocks	```json {...} ```	{...}
Single quotes	{'a': 'b'}	{"a": "b"}
Unquoted keys	{a: 1}	{"a": 1}
Trailing commas	{"a": 1,}	{"a": 1}
Comments	{"a": 1} // comment	{"a": 1}
Unclosed brackets	{"a": 1	{"a": 1}
Special numbers	{"a": NaN}	{"a": null}
Hex/binary numbers	{"a": 0xff}	{"a": 255}

Individual Fixers

import {
  extractFromMarkdown,
  extractJSONFromText,
  fixSingleQuotes,
  fixUnquotedKeys,
  fixTrailingCommas,
  tryCloseBrackets,
  removeJSONComments,
  fixSpecialNumbers
} from 'valai';

// Use individual fixers for fine-grained control
const text = extractFromMarkdown('```json\n{}\n```').text;
const fixed = fixTrailingCommas('{"a": 1,}');

Error Handling

const result = schema.safeParse(invalidData);

if (!result.success) {
  // Structured errors
  console.log(result.error.issues);
  // [{ code: 'invalid_type', path: ['name'], message: '...' }]

  // Flattened format
  console.log(result.error.flatten());
  // { formErrors: [], fieldErrors: { name: ['...'] } }

  // Formatted string
  console.log(result.error.format());
}

Type Inference

import { v } from 'valai';
import type { infer as Infer } from 'valai';

const UserSchema = v.object({
  name: v.string(),
  age: v.number().optional()
});

// Using v.infer
type User = v.infer<typeof UserSchema>;

// Using imported Infer type
type User2 = Infer<typeof UserSchema>;

// Input type (before transforms)
type UserInput = v.input<typeof UserSchema>;

// Output type (after transforms)
type UserOutput = v.output<typeof UserSchema>;

Comparison with Zod

Feature	valai	Zod
Schema definition	Same API	Same API
Type inference	Full support	Full support
LLM parsing mode	parseLLM()	Manual
JSON repair	Built-in	External
Markdown extraction	Built-in	Manual
Type coercion	Auto in LLM mode	Manual coerce
OpenAI export	toOpenAI()	Manual
Claude export	toClaude()	Manual
Gemini export	toGemini()	Manual
AI metadata	.describe(), .examples()	.describe() only
Partial on failure	Yes	No

Run Benchmarks

npx vitest bench --run

API Reference

Schema Methods

Method	Description
.parse(data)	Strict parse, throws on error
.safeParse(data)	Safe parse, returns result object
.parseLLM(data, options?)	LLM-friendly parse with repair
.describe(text)	Add description for AI
.examples(values)	Add examples for AI
.optional()	Make optional
.nullable()	Make nullable
.default(value)	Set default value
.toJSONSchema(options?)	Export as JSON Schema
.toOpenAI(options)	Export for OpenAI
.toClaude(options)	Export for Claude
.toGemini(options)	Export for Gemini

LLM Parse Options

interface LLMParseOptions {
  coerce?: boolean;              // Enable type coercion (default: true)
  repair?: boolean;              // Enable JSON repair (default: true)
  extractFromMarkdown?: boolean; // Extract from code blocks (default: true)
  useDefaults?: boolean;         // Use default values (default: true)
}

License

MIT