How can I test PHP skills in a interview?

  • My company needs to hire a PHP developer, but nobody has PHP knowledge in my company and we find difficult to test for PHP skills. If it were a C/Java developer I would ask him to write a quick implementation of the Game of Life, but PHP is a completely different language.

    I saw this test with interest:

    Anyone else has more suggestions?

    Interesting test, doesn't cover SQL injection though which I would certainly cover. I guess that test's a good way to test their ability to determine their familiarity with how PHP treats variables and not much else.

    Whatever you do, don't ask questions regarding the spelling of standard function names. PHP function naming is so inconsistent.

    I would worry less about their PHP chops and more if they can program, work with the team, understand web security, etc.

    and how could I test that? Could you suggest some questions?

    @Mascarpone Ask them about XSS (Cross Site Scripting), XSRF (Cross Site Request Forgery), SQL Injection, lack of proper server-side data validations, etc. Write up some basic examples of these security holes and ask them to find as many issues as they can.

    If nobody of your company knows PHP well, then the best way for you is to use some skills testing service. - I like this one. And then, if the result will be good, you can ask him to write some PHP code. For example, there are students and subjects in database. Ask him to write the HTML-form, where the director edits the marks in the table (Students are in left column, Subjects are in top row, Marks are at the intersection).

    @Joseph I came across that site a little earlier and it looks really helpful!

  • yannis

    yannis Correct answer

    9 years ago


    • Ask the candidate to write code
    • Ask the candidate to read code

    If you do ask the candidate to write code make sure that:

    • The code is non trivial but small
    • You allow access to the manual and the internet

    If you do ask the candidate to read code make sure that:

    • The code has some trivial errors
    • The code has some non trivial errors
    • The code works fine, but it can be easily optimized

    You can use three or more different pieces of code, start from the simpler one and only advance to the next if you see that the candidate copes with ease. Throw in some recursion, to spice things up.


    Ask for a detailed list of PHP resources the candidate uses. Books, blogs, forums, magazines, etc. That's how my current employers found out about StackOverflow.

    If the candidate mentions StackOverflow or Programmers, you should NOT ask or try to find out their username. If they wanted to advertise their reputation they would have included a Careers 2.0 link on their resume.


    Every PHP developer should know of the most popular PHP frameworks:

    and be fluent in at least one of them. You can have a few code samples ready for each one and ask the candidate to read and explain them, after they tell you which one they are more familiar with.

    Debugging & Profiling

    I've always felt that PHP developers are lacking debugging and profiling skills (perhaps only the PHP developers I've worked with). If during the discussion you find out that the candidate actively uses xdebug, don't bother with the rest of the interview and just hire them. ;)

    Input sanitization

    This is important. You can start with a discussion on why it's important and then ask for the most common methods to achieve it. This discussion will help you on what to ask.

    Some hints:

    PHP snafus

    You can find a lot of PHP snafus in this excellent discussion. If you are interviewing for a senior position you should definetaly ask on some of those. Some examples:

    PHP's handling of numeric values in strings:

    "01a4" != "001a4" // true
    "01e4" == "001e4" // also true

    Valid PHP code:


    In PHP, a string is as good as a function pointer:

    $x = "foo";
    function foo(){ echo "wtf"; }
    $x(); # "wtf"   

    Unit testing

    Need I say more?


    A good PHP developer should combine a variety of skills & talents:

    • A good understanding of HTTP
    • A good understanding of Apache configuration (Even if you use a different web server at your company)
    • At least a basic understanding of JavaScript
    • A great understanding of HTML / CSS

    The list goes on and on. Make sure you tailor the interview to the specific needs of the job opening, you don't want to hire just a good developer but a good developer that's great at what you immediately need him / her to do.

    Good answer overall, but I disagree on the 'frameworks' part and the 'basic performance' part. Whether you know a certain framework or not doesn't say much about your qualities as a programmer. About the performance part: if you're optimizing at this level, you probably shouldn't be using PHP in the first place. I make choices between the alternatives you list dozens of times each day, but always based on readability and functionality, not performance. The correct answer to these performance questions is "it doesn't matter most of the time."

    @tdammers `Whether you know a certain framework or not doesn't say much about your qualities as a programmer.`: Yes, but it makes it easier to integrate yourself in a team. Most teams I've work with used some kind of framework (floss or in house). As for the performance, I totally disagree with you on all points: The optimizations can save you a lot of grief on several common scenarios, like big imports / exports. And properly optimized PHP is a fantastic platform to work on, I wouldn't change it for anything. And never found a valid reason to do so.

    @YannisRizos: While it most likely makes it easier to integrate in a team you are assuming that in the OP's company they use one of these popular frameworks, but if they are not then knowing either of the frameworks would prove nothing. Perhaps you meant this part as a way to test his ability to work with *a* framework rather than with *those* frameworks? (Point in case: in the company I work for we use an in-house developed framework)

    I disagree with `you should NOT ask or try to find out their username`. If they are on SO, and don't want to show you their profile, then they are hiding something. Likewise many employers ask to see FB accounts and the like.

    @Petah That doesn't make any sense at all, especially at the interview stage and I would avoid working at a company that asks people to reveal information like that during the interview. The whole "hiding something" reasoning is perverse, imho, I don't care for my employer knowing how I spend my free time, and that's just about it. If I'm interested in publicizing my Programmers account on my own, that's a different story...

    Personally I have never asked for this information, but have been asked. I do somewhat agree that if I am going to spend 25%-35% of my time with someone then I would like to know a bit about there personality before I commit to it.

    @Petah Well I honestly hope future employers don't try to get to know my personality through my Programmers activities (who would want to spend 25%-35% of their time with an evil nazi mod ;)

    Disagree with the framework thing. Good, modern practice is to use applicable components from frameworks using composer that you require rather than using an entire framework. In fact, the same can be said in the JS world now too..

    @Yannis just wondering what if the person doesn't know any framework and just php

    "01e4" == "001e4" is NOT true. They will be compared as strings and will return false.

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