mojo-validation

Input validation and schema enforcement for Mojo applications. A pure Mojo alternative to Python's Pydantic.

Features

• Field Constraints: Required, min/max length, range, patterns
• Format Validators: Email, URL, alpha, numeric, alphanumeric
• Schema Validation: Pydantic-style model validation
• Rich Errors: Detailed error messages with field names and values

Installation

Add to your pixi.toml:

[workspace.dependencies]
mojo-validation = { path = "../mojo-libs/mojo-validation" }

Usage

Quick Validation

from mojo_validation import validate_required, validate_email, validate_range

# These raise on failure
validate_required("name", user_name)
validate_email("email", user_email)
validate_range("age", user_age, 0, 150)

Check Validators (Return Optional[FieldError])

from mojo_validation import check_required, check_email, check_positive

var err = check_required("name", "")
if err:
    print("Error:", err.value())

var email_err = check_email("email", "invalid")
if email_err:
    print("Invalid email:", email_err.value().message)

Field Constraints

from mojo_validation import StringField, IntField, FloatField

# String field with constraints
var email_field = StringField("email")
    .set_required()
    .set_email()
    .set_max_length(255)

var errors = email_field.validate(user_input)
if errors.has_errors():
    print(errors)

# Int field with range
var age_field = IntField("age")
    .set_required()
    .set_range(0, 150)

# Float field with bounds
var rate_field = FloatField("rate")
    .set_positive()
    .set_lte(100.0)

Schema Validation

from mojo_validation import SchemaValidator, StringField, IntField

var validator = SchemaValidator()

# Define fields
var email = StringField("email")
    .set_required()
    .set_email()
validator.add_string_field(email)

var username = StringField("username")
    .set_required()
    .set_min_length(3)
    .set_max_length(20)
    .set_alphanumeric()
validator.add_string_field(username)

var age = IntField("age")
    .set_gte(18)
    .set_lte(120)
validator.add_int_field(age)

# Validate inputs
validator.validate_string("email", user_email)
validator.validate_string("username", user_name)
validator.validate_int("age", user_age)

if validator.is_valid():
    print("All inputs valid!")
else:
    print(validator.errors())

Validation Result

from mojo_validation import ValidationResult

fn parse_and_validate(data: String) -> ValidationResult[UserData]:
    var errors = ValidationError()

    # ... validation logic ...

    if errors.has_errors():
        return ValidationResult[UserData](errors)

    return ValidationResult[UserData](parsed_user)

var result = parse_and_validate(input)
if result.is_valid():
    process(result.value())
else:
    handle_errors(result.errors())

API Reference

Validator Functions

Function	Description
check_required(field, value)	Check value is not empty
check_min_length(field, value, min)	Check minimum length
check_max_length(field, value, max)	Check maximum length
check_length(field, value, min, max)	Check length in range
check_gt(field, value, threshold)	Check value > threshold
check_gte(field, value, threshold)	Check value >= threshold
check_lt(field, value, threshold)	Check value < threshold
check_lte(field, value, threshold)	Check value <= threshold
check_range(field, value, min, max)	Check value in range
check_positive(field, value)	Check value > 0
check_non_negative(field, value)	Check value >= 0
check_email(field, value)	Check email format
check_url(field, value)	Check URL format
check_alpha(field, value)	Check alphabetic only
check_alphanumeric(field, value)	Check alphanumeric only
check_numeric(field, value)	Check numeric string
check_one_of(field, value, options)	Check value in list

StringField Methods

Method	Description
set_required()	Mark as required
set_min_length(n)	Set minimum length
set_max_length(n)	Set maximum length
set_length(min, max)	Set length range
set_email()	Validate as email
set_url()	Validate as URL
set_alpha()	Alphabetic only
set_alphanumeric()	Alphanumeric only
set_numeric()	Numeric string only
set_one_of(values)	Restrict to list
validate(value)	Run all validations

IntField Methods

Method	Description
set_required()	Mark as required
set_gt(n)	Greater than
set_gte(n)	Greater than or equal
set_lt(n)	Less than
set_lte(n)	Less than or equal
set_range(min, max)	Value in range
set_positive()	Positive only (> 0)
set_non_negative()	Non-negative (>= 0)
validate(value, is_set)	Run all validations

FloatField Methods

Method	Description
set_required()	Mark as required
set_gt(n)	Greater than
set_gte(n)	Greater than or equal
set_lt(n)	Less than
set_lte(n)	Less than or equal
set_range(min, max)	Value in range
set_positive()	Positive only
validate(value, is_set)	Run all validations

Error Handling

from mojo_validation import ValidationError, FieldError

var errors = ValidationError()
errors.add("email", "is required")
errors.add("age", "must be positive", "-5")

print(errors.count())       # 2
print(errors.has_errors())  # True
print(errors.first_error()) # "email: is required"
print(errors)               # Full error report

License

Apache 2.0

Part of mojo-contrib

This library is part of mojo-contrib, a collection of pure Mojo libraries.