#validation #api #validator


Common validation functions (email, url, length, …) and trait

10 releases (5 breaking)

0.7.1 Jul 27, 2018
0.6.3 Dec 5, 2017
0.6.2 Nov 8, 2017
0.4.0 Jan 30, 2017
0.1.0 Dec 28, 2016

#2 in Email

Download history 167/week @ 2018-06-15 168/week @ 2018-06-22 314/week @ 2018-06-29 178/week @ 2018-07-06 305/week @ 2018-07-13 263/week @ 2018-07-20 224/week @ 2018-07-27 527/week @ 2018-08-03 390/week @ 2018-08-10 201/week @ 2018-08-17 251/week @ 2018-08-24 258/week @ 2018-08-31 339/week @ 2018-09-07

1,018 downloads per month
Used in 3 crates

MIT license

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Macros 1.1 custom derive to simplify struct validation inspired by marshmallow and Django validators. It relies on the proc_macro feature which is stable since Rust 1.15.

By default all args to a validate must be strings if you are using stable. However, if you are using nightly, you can also activate the attr_literals feature to be able to use int, float and boolean as well.

A short example:

extern crate validator_derive;
extern crate validator;
extern crate serde_derive;
extern crate serde_json;

// A trait that the Validate derive will impl
use validator::{Validate, ValidationError};

#[derive(Debug, Validate, Deserialize)]
struct SignupData {
    mail: String,
    phone: String,
    site: String,
    #[validate(length(min = "1"), custom = "validate_unique_username")]
    #[serde(rename = "firstName")]
    first_name: String,
    #[validate(range(min = "18", max = "20"))]
    age: u32,

fn validate_unique_username(username: &str) -> Result<(), ValidationError> {
    if username == "xXxShad0wxXx" {
        // the value of the username will automatically be added later
        return Err(ValidationError::new("terrible_username"));


match signup_data.validate() {
  Ok(_) => (),
  Err(e) => return e;

An error has the following structure:

#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
pub struct ValidationError {
  pub code: Cow<'static, str>,
  pub message: Option<Cow<'static, str>>,
  pub params: HashMap<Cow<'static, str>, Value>,

The value of the field will automatically be added to the params with a key of value.

Note that validator works in conjunction with serde: in the example we can see that the first_name field is renamed from/to firstName. Any error on that field will be in the firstName key of the hashmap, not first_name.

If you are adding a validation on a Option<..> field, it will only be ran if there is a value. The exception being must_match that doesn't currently work with Option due to me not finding a use case for it. If you have one, please comment on https://github.com/Keats/validator/issues/7.


You will need to import the Validate trait, and optionally use the attr_literals feature.

The validator crate can also be used without the custom derive as it exposes all the validation functions and types.


The crate comes with some built-in validators and you can have several validators for a given field.


Tests whether the String is a valid email according to the HTML5 regex, which means it will mark some esoteric emails as invalid that won't be valid in a email input as well. This validator doesn't take any arguments: #[validate(email)].


Tests whether the String is a valid URL. This validator doesn't take any arguments: #[validate(url)];


Tests whether a String or a Vec match the length requirement given. length has 3 integer arguments:

  • min
  • max
  • equal

Using equal excludes the min or max and will result in a compilation error if they are found.

At least one argument is required with a maximum of 2 (having min and max at the same time).


#[validate(length(min = "1", max = "10"))]
#[validate(length(min = "1"))]
#[validate(length(max = "10"))]
#[validate(length(equal = "10"))]


Tests whether a number is in the given range. range takes 2 number arguments: min and max.


#[validate(range(min = "1", max = "10"))]
#[validate(range(min = "1", max = "10.8"))]
#[validate(range(min = "1.1", max = "10.8"))]


Tests whether the 2 fields are equal. must_match takes 1 string argument. It will error if the field mentioned is missing or has a different type than the field the attribute is on.


#[validate(must_match = "password2")]


Tests whether the string contains the substring given or if a key is present in a hashmap. contains takes 1 string argument.


#[validate(contains = "gmail")]


Tests whether the string matchs the regex given. regex takes 1 string argument: the path to a static Regex instance.


#[validate(regex = "ALLOWED_USERNAMES_RE")]


Test whetever the string is a valid credit card number.




Tests whether the String is a valid phone number (in international format, ie. containing the country indicator like +14152370800 for an US number — where 4152370800 is the national number equivalent, which is seen as invalid). To use this validator, you must enable the phone feature for the validator_derive crate. This validator doesn't take any arguments: #[validate(phone)];


Calls one of your function to do a custom validation. The field will be given as parameter and it should return a Option<String> representing the error code, if there was an error.


#[validate(custom = "validate_something")]
#[validate(custom = "::utils::validate_something")]

Struct level validation

Often, some error validation can only be applied when looking at the full struct, here's how it works here:

#[derive(Debug, Validate, Deserialize)]
#[validate(schema(function = "validate_category", skip_on_field_errors = "false")]
struct CategoryData {
    category: String,
    name: String,

The function mentioned should return a Option<(String, String)> where the tuple is (key error, error code) and will be called after validation is done for all fields. This means that the error can be reported on an existing field or on a new key.

The skip_on_field_errors defaults to true if not present and will ensure that the function is not called if an error happened while validating the struct fields.

Any error on the schema level validation will appear in the key __all__ of the hashmap of errors.

Message and code

Each validator can take 2 optional arguments in addition to their own arguments:

  • message: a message to go with the error, for example if you want to do i18n
  • code: each validator has a default error code (for example the regex validator code is regex) but it can be overriden if necessary, mainly needed for the custom validator

For example, the following attributes all work:

#[validate(email(message="Email %s is not valid"))]
#[validate(email(code="mail", message="Email %s is not valid"))]



0.7.0 (2018/05/29)

  • Feature gate the card validator

0.6.2 (2017/11/08)

  • Fix credit card validation being incorrect in enum

0.6.1 (2017/11/08)

  • Add international phone number and credit card validation

0.6.0 (2017/08/12)

  • Re-design ValidationError and Validate trait


0.7.1 (2018/06/28)

  • Update dependencies

0.7.0 (2018/05/29)

  • Feature gate the card validator

0.6.5 (2018/04/14)

  • Fix path for regex starting with ::
  • Update syn and quote

0.6.4 (2018/03/20)

  • Support Option<Option<T>> types

0.6.3 (2018/03/19)

  • Fix path for custom validators starting with ::

0.6.2 (2018/03/17)

  • Update syn and quote

0.6.1 (2017/11/08)

  • Add international phone number and credit card derive

0.6.0 (2017/08/12)

  • Change generated code to make the new design of errors work


0.5.0 (2017/05/22) > validator_derive only

  • Fix range validator not working on Option
  • Update to serde 1.0

0.4.1 (2017/02/14) > validator_derive only

  • Fix potential conflicts with other attributes

0.4.0 (2017/01/30)

  • Validators now work on Option field and struct/fields with lifetimes

0.3.0 (2017/01/17)

  • Add contains and regex validator
  • BREAKING: change Errors type to be a newtype in order to extend it

0.2.0 (2017/01/17)

  • Remove need for attr_literals feature
  • Fix error when not having validation on each field
  • Add struct level validation
  • Add must_match validator


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