Google Page Speed vs Yahoo YSlow

I try to stay away from cutting edge releases and let things cool off. But YSlow is one of my favorite web development toys tools and newly released Page Speed is perfect rival for it.

So two tools, two huge companies, both want to help us have better web pages. Who is better?


I am no optimization guru. Just a techie who likes fast and responsive sites and wants his blog to be one. I guess exactly someone such convenient and simple to use tools are made for.

What they do

  • both YSlow and Page Speed are plugins for Firebug (which in turn is Firefox plugin);
  • both benchmark web page and analyze components to provide checklist of things that can be corrected and improved for better site load and rendering speeds;
  • both seem to be based on research of Steve Souders who created YSlow while he worked at Yahoo and now works on same things in Google.

Strong features

Since both tools use roughly same set of rules for their evaluations their core function is almost identical.



What differs are additional functions.

Page Speed

  • much more attention to CSS with extended advice on selectors - that is quite original (and, as some put it, questionable);
  • awesome Page Speed Activity function that is similar to page load timers but provides load graphs in real time.


  • latest version got massive interface update with convenient visualizations and sorting capabilities, as well as option to print checklist;
  • different (editable) profiles to separate needs of high traffic sites from smaller ones;
  • boils results down to single grade that frankly tells you how much your site rocks (sucks).


While YSlow had remedied my last gripes (mostly habit of assuming my tiny blog could benefit from worldwide content delivery network) Page Speed brought fresh ones.

I had noticed that Page Speed offers minimized versions of scripts and images already from my hard drive (these have to be requested manually in YSlow). And bingo – Page Speed created two folders for its temporary files in my profile folder.

  • not Firefox extensions folder;
  • not temporary folder;
  • not local settings;
  • not application data.

Which would all seem like sane choice unlike profile root. At least it had courtesy to delete files (not folders) on closing Firefox.

Update Page Speed now uses sane temporary folders for those files on all platforms. :) Excused on this one.

Frankly large reason I try to stay away from desktop software by Google is their sickening habit to treat my PC as their own, filling it with files and background services as they see fit. Is there no one working for them who has clue about portable?


While Page Speed brings some new powerful functions to the table, overall first release feels like what it is – internal tool released to the public.

YSlow has edge – around for longer, more developed and more convenient.

In the long run if Page Speed can throw YSlow from the throne will depend on amount of effort and open source contributions it gets.

Google Page Speed http://code.google.com/speed/page-speed/

Yahoo YSlow http://developer.yahoo.com/yslow/

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  • Phil #

    Couldn't agree more, it'd be nice if Page Speed gave you some sort of overall grade that you could use to assess your pages overall performance. I'm also not sure about this whole "lets develop the app in the quiet and suddenly make it go open source for a big impact" attitude that Google seems to adopt.
  • Rarst #

    @Phil I guess Google tries to keep its image high. It's probably easier to predict how will product fare in real conditions if you have years of internal usage data first. If Google lets too many projects fail their reputation would be notches lower than it is.
  • Richard Rabbat #

    We chose to use the home directory so people could navigate easily to pick up optimized images or minified JavaScript and the like; some of our users really liked that. obviously, many don't and we filed a tracking bug and are working on fixing it to default to a tmp directory
  • Rarst #

    @Richard Rabbat Well, Page Speed generates direct link to file from its interface so physical location is hardly an issue for that. In some scenarios (using with portable Firefox for example) non-standard directory is much more of privacy/security issue than using temporary one. Thanks for dropping by and good luck with development! Can't say YSlow got lazy (on the contrary it is quite active lately) but some competition never hurts. :)
  • Richard Rabbat #

    we released an updated version of Page Speed that uses temp directories and doesn't touch home directories. I hope this helps
  • Rarst #

    @Richard Rabbat Thank you! I had updated post accordingly. :) Since YSlow is lagging behind in Firefox 3.5 compatibility I am going to see much more of Page Speed in some time. Keep up nice pace and good luck in development.
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  • Web application development #

    Very helpful comparison of YSlow and Page Speed. Of course Google's Page Speed is a useful new tool for optimisation of your website. However, it's quantity over quality, top priority is given to speed (then again maybe it's just what you need): for example, CSS selector doesn't allow you to build object-oriented CSS. So firstly you must set your goals and only then choose YSlow or Page Speed for yourself. So in my opinion Yslow is the more reliable and convinient tool, I agree with the author. By the way Chrome and Safari have a similar tool - The WebKit Inspector. I'm looking forward when Opera will get something like this too.
  • Rarst #

    Actually Opera has development tools called Dragonfly for some time already. They are working slowly on it (it is alpha-something at moment) but it is already quite useful.
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  • Hadith #

    Thanks for the enlightenment, Im using pagespeed now but I guess I have to try yslow now.
  • Rarst #

    @Hadith You are welcome. :) Actually either of tools does fine job, I mostly use both and hadn't decided to drop one yet.
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  • Eddie Jaoude #

    Both tools have their pros/cons. I really like their beaconing facility, so I can save historic data and generate reports from them. From this I went and created a free online portal pageshow.jaoudestudios.com where users can beacon their results privately to their account from yslow & page speed (hopefully also httpfox when they add beacon facility - httpwatch equivalent), these results are also validated against w3c. More reports coming soon, any suggestions are welcome.
  • Rarst #

    @Eddie Jaoude Interesting feature with beacons, never tried that. :) I had bookmarked your page to check out.
  • Dan Anos #

    I think that YSlow Should be taken with a pinch of salt, after all, Google.Com gets a "C" Grade.
  • Rarst #

    @Dan Anos google.com is minimalistic page with very few bottlenecks. It is worth it to strive for ideal YSlow score? Not really. But that isn't the reason to ignore it either, there is plenty of very solid data in there.
  • Hemal Shah #

    I got to know more abt Page Speed and Y!Slow from my friends see them as a challenge in web development. I am using GTMetrix to gauge the performance since I am not a fan of development and testing on Firebug. Do any one have any idea, if the results are same for the plug ins and GTMetrix?
  • Rarst #

    @Hemal Shah I did a post on GTmetrix as well. You cannot choose YSlow profiles in GTmetrix, so results will be slightly different from regular YSlow running with different profile.
  • Hemal Shah #

    @Rarst Thanks dude for a very quick reply. :)
  • Mahendra Yadav #

    I am confused. Page speed is giving me decent score but y slow is not. Also how do I combine java script ?
  • Rarst #

    @Mahendra Yadav They are similar, but not identical. Also pay attention to profile used in YSlow. As for combining JavaScript that can be done by hand or by tools for that. It can easily break some scripts, so really it's very case by case what can and should be combined.
  • Prithvi #

    Google Page Speed is surely more efficient as being a part of google it helps in optimizing the content more quickly with webmasters tools. In my case, Google Page speed is giving decent reports, but Yslow is not. Can you suggest a way to get decent performance record from Yahoo Yslow also??
  • Rarst #

    @Prithvi Yahoo itself provides plenty of advice about improving scores.
  • xakbox #

    thanks for the review so wht i am going to try is use both of them .. so i hope ma web will make both of them happy .. :)
  • techtt #

    yslow shows better results than page speed
  • Sajjad Shah #

    Wow great collection of web page tools thanks normally I used web page analyzer…