Validation

env.zig provides built-in validators and schema-based validation with error and warning support.

Validation Levels

Each validation result has a level field:

Level	Meaning
.err	Required field missing or invalid — must be fixed
.warning	Optional field missing or invalid — informational

Condition	Level
Required field missing	.err
Required field present but invalid	.err
Optional field missing (has validators or description)	.warning
Optional field present but invalid	.warning
Optional field missing (no validators, no description)	Silent (no result)

Built-in Validators

Validator	Description
validators.required	Value must not be empty
validators.boolean	Value must be a valid boolean (true/false/yes/no/1/0/on/off)
validators.integer	Value must be a valid integer
validators.float	Value must be a valid float
validators.url	Value must be a valid URL
validators.email	Value must be a valid email address
validators.ipv4	Value must be a valid IPv4 address
validators.hostname	Value must be a valid hostname
validators.port	Value must be a valid port number (0-65535)
validators.range(min, max)	Value must be within the given range
validators.minLength(min)	Value must be at least min characters
validators.maxLength(max)	Value must be at most max characters
validators.oneOf(allowed)	Value must be one of the allowed values

Schema Definition

const env_mod = @import("env");

const schema = env_mod.schema.Schema{
    .fields = &.{
        .{
            .key = "DATABASE_URL",
            .required = true,
            .validators_list = &.{ env_mod.validator.validators.required, env_mod.validator.validators.url },
            .description = "Database connection URL",
        },
        .{
            .key = "PORT",
            .required = true,
            .validators_list = &.{ env_mod.validator.validators.required, env_mod.validator.validators.integer },
            .description = "Server port",
        },
        .{
            .key = "LOG_LEVEL",
            .required = false,
            .default_value = "info",
            .validators_list = &.{env_mod.validator.validators.oneOf(&.{ "debug", "info", "warn", "error" })},
            .description = "Logging level",
        },
        .{
            .key = "API_KEY",
            .required = false,
            .validators_list = &.{env_mod.validator.validators.required},
            .description = "API secret key",
        },
    },
};

Running Validation

const errs = env.validate(schema);

var has_errors = false;
var has_warnings = false;

for (errs) |err| {
    if (err.level == .err) {
        if (!has_errors) {
            try stdout.print("Errors:\n", .{});
            has_errors = true;
        }
        try stdout.print("  [ERROR] {s}: {s}\n", .{ err.key, err.message });
    } else {
        if (!has_warnings) {
            try stdout.print("\nWarnings:\n", .{});
            has_warnings = true;
        }
        try stdout.print("  [WARN]  {s}: {s}\n", .{ err.key, err.message });
    }
}

if (!has_errors and !has_warnings) {
    try stdout.print("Validation passed!\n", .{});
}

Default Values

Fields with default_value or default_fn are auto-populated if missing:

.{
    .key = "TIMEOUT",
    .required = false,
    .default_value = "30",
    .validators_list = &.{env_mod.validator.validators.integer},
},

Custom Validators

Create a custom validator by implementing the ValidatorFn signature:

fn myValidator(value: []const u8) ?[]const u8 {
    if (value.len < 3) return "must be at least 3 characters";
    return null;
}

See Also

• Getting Started for configuration options
• Validators Reference for all built-in validators
• API Reference for the full API