@nikitha, welcome to Webmasterworld... g1smd offers excellent advice. I personally rely on my server logs for that information. Are you new to running a website?
This is potentially two different questions.
#1 You know that 404 errors exist, because you've found them via GWT or similar. Now you want to find out where these bad links are coming from in the first place. Wander through the Forums and you may conclude that much of the time it isn't worth the trouble.*
#2 You want to know whether your site is drawing 404 errors.
Unless you've got an unspeakably complicated site, you need not worry about internal bad links. A quick run with the link checker of your choice will turn up any problems.
* I just took a quick detour to gwt. The latest "not found" is
404 (Not found), ostensibly linked from "1 pages". (Um, g###, have you any idea how easy it is to code that to make it grammatical?) That one page(s) turns out to be some everything-but-the-kitchen-sink site that I've never heard of. Oh, I am so going to seek them out and make them fix the link. Yeah. You betcha. Especially since my page-- minus the "CachedYou"-- doesn't even have any content that belongs in that kitchen sink.
I agree with lucy, it depends on what you want to accomplish, if you want to verify if your site is delivering 404 Xenu may be a good tool to use, if you would like to discover which pages links to a 404 you can put some strings with php like:
this will show in your analytics as soon as someonw see it.
If you’re registered with Google Webmaster Tools, you can view the list of 404 errors that the Googlebot has come across.
You can also use the 404 Notifier plugin, which can notify you via email or RSS feed whenever a 404 error is thrown.
the best place to find the 404 errors is the webmaster tools for one simple fact also that it shows the 404 for the ones which the google bot is actually looking for!
Certainly not "every", and the data needs to be read with a great deal of caution.
Just because an error is reported as "404" that isn't necessarily the actual status code your server returned.
I think the Bing wmt equivalent may be more useful than Google's, because it's broken into smaller, discrete pieces. What I especially like is that it tells you how many links you've got to each individual problem URL in all categories. I don't know if this means internal links or all links from everywhere; currently mine are all at zero, meaning that they're Bing's problem, not mine.
Google Webmaster list the source that is pages that link to 404 pages as well.
You can check it at google webmaster tool.
Xenu link #*$!h
Screaming Frog SEO spider
Now Bing also have a Webmaster tool as Google has, from there you will also be able to find 404 errors..Generally you dnt have to worry about 404.
so. you can easily use google and its web master tools that will help you in this issue. you are to sing in web master account in the google, then the category crawl errors. click it and observe all the 404 error pages.
If you want to check on your 404s in live mode, you can create a 404 page which emails you every time it's called. It can tell you what was a request, and what/who requested it, and whatever else PHP can derive from it.
Use Webmaster Tools for this.
Google webmaster tools is the best options to find out 404 server errors. You can check such as broken link tools also like, Xenu, Screaming Frog and through plugins.
You can find the error reports through the following sources.
Google Webmasters Tools
Broken Link Checker.