9 ms·

Facebook adding “fbclid” parameter to outbound links

135 points by hiby007 8y ago

berbec 8y ago
I can see urls eventually being thousands of characters long with referral links daisy chained.
- cremp 8y ago
  Some already are. A lot of malicious links are just base64'ed to another redirect service; to another base64'ed address (continue as long as your head can keep up.)
  - chopin 8y ago
    I'd expect something like uBlock stripping this off.
- kageneko 8y ago
  I use Neat URL[0] with Firefox to strip things like that from URLs. 0: https://addons.mozilla.org/en-US/firefox/addon/neat-url/ https://addons.mozilla.org/en-US/firefox/addon/neat-url/
  - guitarbill 8y ago
    That's cool, but only really protects the surfer. Instead of stripping them, you could also either fill them with garbage values, or with more effort, swap the parameters with another link. This would degrade the analytics results, but might be harder to detect. And if enough people used it, you'd get some kind of herd tracking immunity.
  - jphalimi 8y ago
    Do you know if the rewrite happens before a user clicks a link? If it happens after, the data ends up actually being sent out to their server...
- wolco 8y ago
  If I remember there is a 1024 character limit.
  - extra88 8y ago
    There isn't. HTTP doesn't define a limit but browsers, servers, and other software can. A quick google search turns up multiple places referring to Internet Explorer's limit being 2,083 characters and other browsers' being tens of thousands of characters. https://stackoverflow.com/questions/15090220/maximum-length-for-url-in-chrome-browser https://stackoverflow.com/questions/15090220/maximum-length-...
mwexler 8y ago
FB has already publicly announced some of these changes: https://www.inc.com/peter-roesler/facebook-to-allow-for-first-party-cookies-on-october-24th.html https://www.inc.com/peter-roesler/facebook-to-allow-for-firs... https://digiday.com/marketing/wtf-what-are-facebooks-first-party-cookies-pixel/ https://digiday.com/marketing/wtf-what-are-facebooks-first-p... Basically, FB is expanding its tracking, allowing 1st party vs. their third party cookie tracking. I suspect the click-id query string is part of that rollout. This helps it get around things like Apple's new ITP (Intelligent Tracking Prevention). 2.0 in Safari.
lolc 8y ago
So they're modifying URL? Facebook is breaking things. But sure, they've run the numbers and decided they don't care. Browsers will now have to resort to removing query parameters to prevent tracking. And websites should really use click-to-enable sharing buttons to prevent Facebook from snooping on everything.
- vntok 8y ago
  My guesstimate is that the number of URLs that are shared on Facebook AND that already have a completely orthogonal "fbclid" parameter is infinitesimal. Maybe among the URLs shared on Facebook there are a few whose servers only respond to a fixed amount of parameters, changing their behaviour when additional unused parameters are appended to the query string, but I imagine that the number of such cases is so low it's not even worth considering. What exactly is Facebook breaking, in your opinion? Would Facebook also break things if they were instead making an async request to the destination and appending a custom header to it, something like "X-Coming-From-Facebook"?
  - lolc 8y ago
    It breaks some server-side caches. And the article itself notes that pages were indexed by Google with the "fbclid" parameter attached. I don't get the part about async requests. What's the scenario?
  - johannes1234321 8y ago
    > What exactly is Facebook breaking, in your opinion? > > Would Facebook also break things if they were instead making an async request to the destination and appending a custom header to it, something like "X-Coming-From-Facebook"? Extra headers are typically ignored, not only since different clients send different headers since the beginning. I know multiple systems which however decode the query string and complain about unknown options or don't accept a query string at all for some resources. On the later case it is ignorance on the other case it is intensive input validation.
    - lmkg 8y ago
kees99 8y ago
I wonder why would fb move away from the well-established utm [1] link parameters to this? From the article, I can't see any functional difference. [1] https://en.wikipedia.org/wiki/UTM_parameters https://en.wikipedia.org/wiki/UTM_parameters
- ryanworl 8y ago
  Many links will already been submitted with UTM parameters and replacing them may have unintended side effects.
- lolc 8y ago
  First time I read about UTM. It looks like those parameters are used to track ad campaigns. They provide metrics over which campaign works best. The "fbclid" parameters on the other hand seems intended to track individual clicks. That is, Facebook wants to keep tracking individuals when they follow links to off-site pages.
  - tomnipotent 8y ago
    It's no different than what every other major player is already doing, they're just now catching up.
    - lolc 8y ago
      I'm not aware of this, but maybe I'm behind the curve? Are you saying that if somebody posts a link on Twitter, that link gets a tracking-parameter appended when people click through? Ar what is it they ar all doing?
- soared 8y ago
  UTM are used for a website's own anayltics while fbclid will link users actions on a website to advertising done on facebook and report on it within fb. UTMs just track where a user came from, fbclid will track who a user is and match it back to fb ads.
- lmkg 8y ago
deleted 8y ago
[deleted]
soared 8y ago
Author failed to do any research, instead of going for the typical "FB is doing something secretive and cryptic" angle. Related links that explain this: https://www.facebook.com/business/news/facebook-attribution-a-measurement-tool-for-todays-digital-advertising-landscape https://www.facebook.com/business/news/facebook-attribution-... https://marketingland.com/facebook-attribution-now-available-to-all-advertisers-250249/amp https://marketingland.com/facebook-attribution-now-available... https://old.reddit.com/r/adops/comments/9pycuk/facebook_attibution_now_available/ https://old.reddit.com/r/adops/comments/9pycuk/facebook_atti... This hn thread is a perfect example of a news bubble. Googling "fbclid" returns the answer in the first result, but hn votes up an article that has no information and treats it as some secret tracking that fb has implemented. HN is excessively biased against any discussion of tracking/analytics on the internet. The community allows no room for true discussion - only blatantly biased opinions. https://www.reddit.com/r/analytics/comments/9o52yw/parameter_called_fbclid_appearing_in_referrals https://www.reddit.com/r/analytics/comments/9o52yw/parameter... Edit - reworded to be less aggressive
- radus 8y ago
  Not really seeing the comments here as jumping to the conclusion that this is a totally secretive and nefarious practice. I think most people here are used to links being instrumented with tracking of this sort.
- maemilius 8y ago
  This article was posted days before any of the links you've given. According to the metadata for the site, it was originally published on 2018-10-14 and last updated 2018-10-16. Facebook's own article about the feature came out 5 days after this article was published. So, at the time, Facebook _was_ being secretive about it. Aside from that one line, the entire article reads more like "this is new, I wonder what it does". Lastly, when I googled "fbclid" the top 3 articles are completely unrelated to Facebook (but, then, I'm not in marketing so this doesn't surprise me) and the forth is this very article.
  - soared 8y ago
    That is fair, I didn't check when the author posted. The first link (for me) when googling fbclid is the reddit post in r/analytics I linked to, which doesn't have a ton of info but gives more than what the author had. Though you're correct, it was posted after the author originally posted, and I can't fault him/her for not checking in again a few days later.
techaddict009 8y ago
This might cause issue of duplication for sites which do not have canonical URL implemented.
- vntok 8y ago
  Google is pretty good at automatically determining which qquery parameters actually modify the response content (pagenb=, id=, q=, etc.) and which do not really (sortby=, highlight=, utm_source=, gclid=) so that should not be a problem.
- canadianwriter 8y ago
  Well yeah... but so would utm's and the millions of other CID's out there. Adobe... GCLID... the list goes on. You need a canonical.
kposehn 8y ago
This is actually fantastic news for advertisers that have their own data warehouses and need to create a better 1-to-1 click tracking to internal user data. This allows much better attribution and testing of incrementality so businesses can tell where their value is truly coming from. I’m pretty excited to see this roll out more broadly.
- teaneedz 8y ago
  And another reason for me to avoid FB links. I'm sure blockers will begin stripping that out. FB just doesn't understand the optics they create.
  - SonnyWortzik 8y ago
    They do, and we do. But the mass sheep audience does not. All they know is: "Does the link work?" and "Can I share it?" That's all.
    - teaneedz 8y ago
      True enough, even though there is nothing but negative sentiment these days toward the Facebook brand. I suppose there is someone even thinking that Portal will be good for their home.
      - rock_hard 8y ago
        I actually ordered a Portal device for each of my family households (parents, grand parents, siblings and in-laws) for Christmas. I think it’s a great product and can’t wait to have mine at home. All the fuss about tracking is non-sense. Ads are a great way to monetize products that you want to make available to a large audience. And obviously as a user you want meaningful ads and not just a bunch of garbage. To do that tracking is necessary...seems like a straightforward value exchange! I also want to note that I buy stuff frequently from ads...some of my most loved items found me through ads! It’s frankly a great way to discover great stuff. Do I sometimes see ads that are not relevant? Sure, just as I see post from friends/family that are not relevant...I just scroll by, easy as that!
pipermerriam 8y ago
There are a number of comments here who seem genuinely happy about this. This is a perspective that is hard for me to understand, largely because I'm strongly in the pro-privacy, anti-tracking ideology. So if you are part of the group who sees this as a good thing, I'm genuinely interested to understand why you see this as a good thing and whether you view the mass surveillance of the general public by advertising companies as bad?
- onlyrealcuzzo 8y ago
  Engineer here: I used to be completely anti-tracking. Then, I started needing analytics for my own business. Without analytics, I wouldn't be able to sell with efficiency, and therefore, I wouldn't have a business. Granted, the anti-consumerist in me thinks maybe as a society we shouldn't be so concerned with our efficiency to sell. But, we live in a capitalist world, and I don't see that changing any time soon. The way I see it now, I'm less concerned about tracking than I am about how big some businesses are -- especially in this space. At every start up I know, they use analytics, and no one is doing anything spooky. But, I'm sure there's plenty of spooky stuff going on at the FAANGAMUs.
  - yurishimo 8y ago
    > FAANGAMU Facebook, Amazon, Apple, Netflix, Google, AirBnb, Microsoft, Uber ? Edit: M for Microsoft, derp
  - eveningcoffee 8y ago
    TL;DR version: I like tracking now because it now makes money for me.
    - al_chemist 8y ago
      As in "I was against child labour, but then I've inherited textile factory in China and paying adult wages is not efficient".
      - 8y ago
patrickyeon 8y ago
This is breaking some links. You might believe it "shouldn't", and a server "should" ignore the added params, but the reality is it's breaking them. This past weekend, I posted a link to an image on Facebook, and FB generated the preview fine, but created a link that 404's. My link: https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg Facebook made: https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg?fbclid=IwAR2MX56GldkA2L5lM94VMK_A420E4FBWsoL7lBlHdtgHs03SpXZQ2rDRUQk https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg?fbclid=IwAR2... I guess if FB really wants, they could make a second fetch to ensure that their added params don't break the third party server. Or could they add a whitelist of domains that use their first-party tracking? I really don't like the end result right now, looking like "the web works" from inside FB, but not when you try to follow this link out of it. I don't believe at all that that is FB's intent here, but it's just one more time that some silo breaks another part of the ecosystem, and to an untrained eye it looks like the third party is the culprit.
- mtkd 8y ago
  I had a quick look at the protocol but couldn't see anything on handling that case Regardless of the protocol - it's not unreasonable to return a 422 or 403 by default for that (malformed) request when first seen - as it would indicate that something sketchy may be going on - which can be whitelisted later
- basch 8y ago
  I believe it was breaking all NYMag links today, appears fixed on NYMags end now. https://www.facebook.com/NewYorkMag https://www.facebook.com/NewYorkMag
  - patrickyeon 8y ago
    Sure, where "fixed on NYMags end" means "NYMags has implemented a workaround because FB broke things".
- lousken 8y ago
  it also broke a couple of safe paste sites for me, that's /r/assholedesign
Asking4AFriend 8y ago
> you should always explicitly set the canonical URL for each page. Could someone explain or give a reliable article that explains this well?
- MuppetMaster42 8y ago
  When Google crawls your site, it doesn't know the difference between two urls with the same path, but with different GET params. Theres no way for them to know whether or not the extra params on the URL change the result page. (i.e. example.com/index.php?post_id=1 and example.com/index.php?comment_id=1 could be very different pages, or they could be the same; you don't know). So in comes the canonical url! This tells Google the proper url required for a specific page. That way if Google gets to a page using two different urls, it can tell that they are the same page. You can list it by adding a tag to your HTML head. You can even do face things like rewrite urls entirely (i.e. If the crawler hits example.com/?category_id=1&item_id=2, you can correct the ugly url by listing the canonical url as example.com/category/1/item/2) https://support.google.com/webmasters/answer/139066?hl=en https://support.google.com/webmasters/answer/139066?hl=en

135 points by hiby007 8y ago

berbec 8y ago

I can see urls eventually being thousands of characters long with referral links daisy chained.

cremp 8y ago
Some already are. A lot of malicious links are just base64'ed to another redirect service; to another base64'ed address (continue as long as your head can keep up.)
- chopin 8y ago
  I'd expect something like uBlock stripping this off.
kageneko 8y ago
I use Neat URL[0] with Firefox to strip things like that from URLs. 0: https://addons.mozilla.org/en-US/firefox/addon/neat-url/ https://addons.mozilla.org/en-US/firefox/addon/neat-url/
- guitarbill 8y ago
  That's cool, but only really protects the surfer. Instead of stripping them, you could also either fill them with garbage values, or with more effort, swap the parameters with another link. This would degrade the analytics results, but might be harder to detect. And if enough people used it, you'd get some kind of herd tracking immunity.
- jphalimi 8y ago
  Do you know if the rewrite happens before a user clicks a link? If it happens after, the data ends up actually being sent out to their server...
wolco 8y ago
If I remember there is a 1024 character limit.
- extra88 8y ago
  There isn't. HTTP doesn't define a limit but browsers, servers, and other software can. A quick google search turns up multiple places referring to Internet Explorer's limit being 2,083 characters and other browsers' being tens of thousands of characters. https://stackoverflow.com/questions/15090220/maximum-length-for-url-in-chrome-browser https://stackoverflow.com/questions/15090220/maximum-length-...

mwexler 8y ago

FB has already publicly announced some of these changes: https://www.inc.com/peter-roesler/facebook-to-allow-for-first-party-cookies-on-october-24th.html https://www.inc.com/peter-roesler/facebook-to-allow-for-firs... https://digiday.com/marketing/wtf-what-are-facebooks-first-party-cookies-pixel/ https://digiday.com/marketing/wtf-what-are-facebooks-first-p... Basically, FB is expanding its tracking, allowing 1st party vs. their third party cookie tracking. I suspect the click-id query string is part of that rollout. This helps it get around things like Apple's new ITP (Intelligent Tracking Prevention). 2.0 in Safari.

lolc 8y ago

So they're modifying URL? Facebook is breaking things. But sure, they've run the numbers and decided they don't care. Browsers will now have to resort to removing query parameters to prevent tracking. And websites should really use click-to-enable sharing buttons to prevent Facebook from snooping on everything.

vntok 8y ago
My guesstimate is that the number of URLs that are shared on Facebook AND that already have a completely orthogonal "fbclid" parameter is infinitesimal. Maybe among the URLs shared on Facebook there are a few whose servers only respond to a fixed amount of parameters, changing their behaviour when additional unused parameters are appended to the query string, but I imagine that the number of such cases is so low it's not even worth considering. What exactly is Facebook breaking, in your opinion? Would Facebook also break things if they were instead making an async request to the destination and appending a custom header to it, something like "X-Coming-From-Facebook"?
- lolc 8y ago
  It breaks some server-side caches. And the article itself notes that pages were indexed by Google with the "fbclid" parameter attached. I don't get the part about async requests. What's the scenario?
- johannes1234321 8y ago
  > What exactly is Facebook breaking, in your opinion? > > Would Facebook also break things if they were instead making an async request to the destination and appending a custom header to it, something like "X-Coming-From-Facebook"? Extra headers are typically ignored, not only since different clients send different headers since the beginning. I know multiple systems which however decode the query string and complain about unknown options or don't accept a query string at all for some resources. On the later case it is ignorance on the other case it is intensive input validation.
  - lmkg 8y ago

kees99 8y ago

I wonder why would fb move away from the well-established utm [1] link parameters to this? From the article, I can't see any functional difference. [1] https://en.wikipedia.org/wiki/UTM_parameters https://en.wikipedia.org/wiki/UTM_parameters

ryanworl 8y ago
Many links will already been submitted with UTM parameters and replacing them may have unintended side effects.
lolc 8y ago
First time I read about UTM. It looks like those parameters are used to track ad campaigns. They provide metrics over which campaign works best. The "fbclid" parameters on the other hand seems intended to track individual clicks. That is, Facebook wants to keep tracking individuals when they follow links to off-site pages.
- tomnipotent 8y ago
  It's no different than what every other major player is already doing, they're just now catching up.
  - lolc 8y ago
    I'm not aware of this, but maybe I'm behind the curve? Are you saying that if somebody posts a link on Twitter, that link gets a tracking-parameter appended when people click through? Ar what is it they ar all doing?
soared 8y ago
UTM are used for a website's own anayltics while fbclid will link users actions on a website to advertising done on facebook and report on it within fb. UTMs just track where a user came from, fbclid will track who a user is and match it back to fb ads.
lmkg 8y ago

deleted 8y ago

[deleted]

soared 8y ago

Author failed to do any research, instead of going for the typical "FB is doing something secretive and cryptic" angle. Related links that explain this: https://www.facebook.com/business/news/facebook-attribution-a-measurement-tool-for-todays-digital-advertising-landscape https://www.facebook.com/business/news/facebook-attribution-... https://marketingland.com/facebook-attribution-now-available-to-all-advertisers-250249/amp https://marketingland.com/facebook-attribution-now-available... https://old.reddit.com/r/adops/comments/9pycuk/facebook_attibution_now_available/ https://old.reddit.com/r/adops/comments/9pycuk/facebook_atti... This hn thread is a perfect example of a news bubble. Googling "fbclid" returns the answer in the first result, but hn votes up an article that has no information and treats it as some secret tracking that fb has implemented. HN is excessively biased against any discussion of tracking/analytics on the internet. The community allows no room for true discussion - only blatantly biased opinions. https://www.reddit.com/r/analytics/comments/9o52yw/parameter_called_fbclid_appearing_in_referrals https://www.reddit.com/r/analytics/comments/9o52yw/parameter... Edit - reworded to be less aggressive

radus 8y ago
Not really seeing the comments here as jumping to the conclusion that this is a totally secretive and nefarious practice. I think most people here are used to links being instrumented with tracking of this sort.
maemilius 8y ago
This article was posted days before any of the links you've given. According to the metadata for the site, it was originally published on 2018-10-14 and last updated 2018-10-16. Facebook's own article about the feature came out 5 days after this article was published. So, at the time, Facebook _was_ being secretive about it. Aside from that one line, the entire article reads more like "this is new, I wonder what it does". Lastly, when I googled "fbclid" the top 3 articles are completely unrelated to Facebook (but, then, I'm not in marketing so this doesn't surprise me) and the forth is this very article.
- soared 8y ago
  That is fair, I didn't check when the author posted. The first link (for me) when googling fbclid is the reddit post in r/analytics I linked to, which doesn't have a ton of info but gives more than what the author had. Though you're correct, it was posted after the author originally posted, and I can't fault him/her for not checking in again a few days later.

techaddict009 8y ago

This might cause issue of duplication for sites which do not have canonical URL implemented.

vntok 8y ago
Google is pretty good at automatically determining which qquery parameters actually modify the response content (pagenb=, id=, q=, etc.) and which do not really (sortby=, highlight=, utm_source=, gclid=) so that should not be a problem.
canadianwriter 8y ago
Well yeah... but so would utm's and the millions of other CID's out there. Adobe... GCLID... the list goes on. You need a canonical.

kposehn 8y ago

This is actually fantastic news for advertisers that have their own data warehouses and need to create a better 1-to-1 click tracking to internal user data. This allows much better attribution and testing of incrementality so businesses can tell where their value is truly coming from. I’m pretty excited to see this roll out more broadly.

teaneedz 8y ago
And another reason for me to avoid FB links. I'm sure blockers will begin stripping that out. FB just doesn't understand the optics they create.
- SonnyWortzik 8y ago
  They do, and we do. But the mass sheep audience does not. All they know is: "Does the link work?" and "Can I share it?" That's all.
  - teaneedz 8y ago
    True enough, even though there is nothing but negative sentiment these days toward the Facebook brand. I suppose there is someone even thinking that Portal will be good for their home.
    - rock_hard 8y ago
      I actually ordered a Portal device for each of my family households (parents, grand parents, siblings and in-laws) for Christmas. I think it’s a great product and can’t wait to have mine at home. All the fuss about tracking is non-sense. Ads are a great way to monetize products that you want to make available to a large audience. And obviously as a user you want meaningful ads and not just a bunch of garbage. To do that tracking is necessary...seems like a straightforward value exchange! I also want to note that I buy stuff frequently from ads...some of my most loved items found me through ads! It’s frankly a great way to discover great stuff. Do I sometimes see ads that are not relevant? Sure, just as I see post from friends/family that are not relevant...I just scroll by, easy as that!

pipermerriam 8y ago

There are a number of comments here who seem genuinely happy about this. This is a perspective that is hard for me to understand, largely because I'm strongly in the pro-privacy, anti-tracking ideology. So if you are part of the group who sees this as a good thing, I'm genuinely interested to understand why you see this as a good thing and whether you view the mass surveillance of the general public by advertising companies as bad?

onlyrealcuzzo 8y ago
Engineer here: I used to be completely anti-tracking. Then, I started needing analytics for my own business. Without analytics, I wouldn't be able to sell with efficiency, and therefore, I wouldn't have a business. Granted, the anti-consumerist in me thinks maybe as a society we shouldn't be so concerned with our efficiency to sell. But, we live in a capitalist world, and I don't see that changing any time soon. The way I see it now, I'm less concerned about tracking than I am about how big some businesses are -- especially in this space. At every start up I know, they use analytics, and no one is doing anything spooky. But, I'm sure there's plenty of spooky stuff going on at the FAANGAMUs.
- yurishimo 8y ago
  > FAANGAMU Facebook, Amazon, Apple, Netflix, Google, AirBnb, Microsoft, Uber ? Edit: M for Microsoft, derp
- eveningcoffee 8y ago
  TL;DR version: I like tracking now because it now makes money for me.
  - al_chemist 8y ago
    As in "I was against child labour, but then I've inherited textile factory in China and paying adult wages is not efficient".
    - 8y ago

patrickyeon 8y ago

This is breaking some links. You might believe it "shouldn't", and a server "should" ignore the added params, but the reality is it's breaking them. This past weekend, I posted a link to an image on Facebook, and FB generated the preview fine, but created a link that 404's. My link: https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg Facebook made: https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg?fbclid=IwAR2MX56GldkA2L5lM94VMK_A420E4FBWsoL7lBlHdtgHs03SpXZQ2rDRUQk https://pbs.twimg.com/media/Byv5uWSIIAEf38C.jpg?fbclid=IwAR2... I guess if FB really wants, they could make a second fetch to ensure that their added params don't break the third party server. Or could they add a whitelist of domains that use their first-party tracking? I really don't like the end result right now, looking like "the web works" from inside FB, but not when you try to follow this link out of it. I don't believe at all that that is FB's intent here, but it's just one more time that some silo breaks another part of the ecosystem, and to an untrained eye it looks like the third party is the culprit.

mtkd 8y ago
I had a quick look at the protocol but couldn't see anything on handling that case Regardless of the protocol - it's not unreasonable to return a 422 or 403 by default for that (malformed) request when first seen - as it would indicate that something sketchy may be going on - which can be whitelisted later
basch 8y ago
I believe it was breaking all NYMag links today, appears fixed on NYMags end now. https://www.facebook.com/NewYorkMag https://www.facebook.com/NewYorkMag
- patrickyeon 8y ago
  Sure, where "fixed on NYMags end" means "NYMags has implemented a workaround because FB broke things".
lousken 8y ago
it also broke a couple of safe paste sites for me, that's /r/assholedesign

Asking4AFriend 8y ago

> you should always explicitly set the canonical URL for each page. Could someone explain or give a reliable article that explains this well?

MuppetMaster42 8y ago
When Google crawls your site, it doesn't know the difference between two urls with the same path, but with different GET params. Theres no way for them to know whether or not the extra params on the URL change the result page. (i.e. example.com/index.php?post_id=1 and example.com/index.php?comment_id=1 could be very different pages, or they could be the same; you don't know). So in comes the canonical url! This tells Google the proper url required for a specific page. That way if Google gets to a page using two different urls, it can tell that they are the same page. You can list it by adding a tag to your HTML head. You can even do face things like rewrite urls entirely (i.e. If the crawler hits example.com/?category_id=1&item_id=2, you can correct the ugly url by listing the canonical url as example.com/category/1/item/2) https://support.google.com/webmasters/answer/139066?hl=en https://support.google.com/webmasters/answer/139066?hl=en