[removed] client-side vs. server-side validation

Question

Which is better to do client side or server side validation?

In our situation we are using

• jQuery and MVC.
• JSON data to pass between our View and Controller.

A lot of the validation I do is validating data as users enter it. For example I use the the keypress event to prevent letters in a text box, set a max number of characters and that a number is with in a range.

I guess the better question would be, Are there any benefits to doing server side validation over client side?

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Awesome answers everyone. The website that we have is password protected and for a small user base(<50). If they are not running JavaScript we will send ninjas. But if we were designing a site for everyone one I'd agree to do validation on both sides.

Answer 1

I came across an interesting link that make a distinction between gross, systematic, random errors.

Client-Side validation suits perfectly for preventing gross and random errors. Typically a max length for texture and input. Do not mimic the server-side validation rule; provide your own gross, rule of thumb validation rule (ex. 200 characters on client-side; n on server-side dictated by a strong business rule).

Server-side validation suits perfectly for preventing systematic errors; it will enforce business rules.

In a project I'm involved in, the validation is done on the server through ajax requests. On the client I display error messages accordingly.

Further reading: gross, systematic, random errors:

https://answers.yahoo.com/question/index?qid=20080918203131AAEt6GO

Answer 2

The benefit of doing server side validation over client side validation is that client side validation can be bypassed/manipulated:

• The end user could have javascript switched off
• The data could be sent directly to your server by someone who's not even using your site, with a custom app designed to do so
• A Javascript error on your page (caused by any number of things) could result in some, but not all, of your validation running

In short - always, always validate server-side and then consider client-side validation as an added "extra" to enhance the end user experience.

Answer 3

Yes, client side validation can be totally bypassed, always. You need to do both, client side to provide a better user experience, and server side to be sure that the input you get is actually validated and not just supposedly validated by the client.

Answer 4

Well, I still find some room to answer.

In addition to answers from Rob and Nathan, I would add that having client-side validations matters. When you are applying validations on your webforms you must follow these guidelines:

Client-Side

1. Must use client-side validations in order to filter genuine requests coming from genuine users at your website.
2. The client-side validation should be used to reduce the errors that might occure during server side processing.
3. Client-side validation should be used to minimize the server-side round-trips so that you save bandwidth and the requests per user.

Server-Side

1. You SHOULD NOT assume the validation successfully done at client side is 100% perfect. No matter even if it serves less than 50 users. You never know which of your user/emplyee turn into an "evil" and do some harmful activity knowing you dont have proper validations in place.
2. Even if its perfect in terms of validating email address, phone numbers or checking some valid inputs it might contain very harmful data. Which needs to be filtered at server-side no matter if its correct or incorrect.
3. If client-side validation is bypassed, your server-side validations comes to rescue you from any potential damage to your server-side processing. In recent times, we have already heard lot of stories of SQL Injections and other sort of techniques that might be applied in order to gain some evil benefits.

Both types of validations play important roles in their respective scope but the most strongest is the server-side. If you receive 10k users at a single point of time then you would definitely end up filtering the number of requests coming to your webserver. If you find there was a single mistake like invalid email address then they post back the form again and ask your user to correct it which will definitely eat your server resources and bandwidth. So better you apply javascript validation. If javascript is disabled then your server side validation will come to rescue and i bet only a few users might have accidentlly disable it since 99.99% of websites use javascript and its already enabled by default in all modern browsers.

Answer 5

You must always validate on the server.

Also having validation on the client is nice for users, but is utterly insecure.

Answer 6

I am just going to repeat it, because it is quite important:

Always validate on the server

and add JavaScript for user-responsiveness.