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Now, I realise the initial response to this is likely to be "you can't" or "use analytics", but I'll continue in the hope that someone has more insight than that.

Google adwords with "autotagging" appends a "gclid" (presumably "google click id") to link that sends you to the advertised site. It appears in the web log since it's a query parameter, and it's used by analytics to tie that visit to the ad/campaign.

What I would like to do is to extract any useful information from the gclid in order to do our own analysis on our traffic. The reasons for this are:

  • Stats are imperfect, but if we are collating them, we know exactly what assumptions we have made, and how they were calculated.
  • We can tie the data to the rest of our data and produce far more accurate stats wrt conversion rate.
  • We don't have to rely on javascript for conversions.

Now it is clear that the gclid is base64 encoded (or some close variant), and some parts of it vary more than others. Beyond that, I haven't been able to determine what any of it relates to.

Does anybody have any insight into how I might approach decoding this, or has anybody already related gclids back to compaigns or even accounts?

I have spoken to a couple of people at google, and despite their "don't be evil" motto, they were completely unwilling to discuss the possibility of divulging this information, even under an NDA. It seems they like the monopoly they have over our web stats.

andre
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Draemon
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  • though, it looks not related comment, but, please allow it. Google's motto in Adword is "be evil". Google sucks all small & mid size business owner's money like a blood trusty vampire. – Mani May 12 '16 at 07:54
  • There is this explanation : https://deedpolloffice.com/blog/articles/decoding-gclid-parameter – bastien Mar 23 '17 at 14:28

11 Answers11

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By far the easiest solution is to manually tag your links with Google Analytics campaign tracking parameters (utm_source, utm_campaign, utm_medium, etc.) and then pull out that data.

The gclid is dependent on more than just the adwords account/campaign/etc. If you click on the same adwords ad twice, it could give you different gclids, because there's all sorts of session and cost data associated with that particular click as well.

(NOTE: According to Google, as of Wednesday, October 5, 2016, Google Click ID (GCLID) will now be generated at impression-time. This means that clicking the same link twice should now yield the same GCLID.)

Gclid is probably not 100% random, true, but I'd be very surprised and concerned if it were possible to extract all your Adwords data from that number. That would be a HUGE security flaw (i.e. an arbitrary user could view your Adwords data). More likely, a pseudo-random gclid is generated with every impression, and if that ad is clicked on, the gclid is logged in Adwords (otherwise it's thrown out). Analytics then uses that number to reconcile the data with Adwords after the fact. Other than that, there's no intrinsic value in the gclid number itself.

In regards to your last point, attempting to crack or reverse-engineer this information is explicitly forbidden in both the Google Analytics and Google Adwords Terms of Service, and is grounds for a permanent ban. Additionally, the TOS that you agreed to when signing up for these services says that it is not your data to use in any way you feel like. Google is providing a free service, so there are strings attached. If you don't like not having complete control over your data, then there are plenty of other solutions out there. However, you will pay a premium for that kind of control.

Google makes nearly all their money from selling ads. Adwords is their biggest money-making product. They're not going to give you confidential information about how it works. They don't know who you are, or what you're going to do with that information. It doesn't matter if you sign an NDA and they have legal recourse to sue you; if you give away that information to a competitor, your life isn't worth enough to pay back the money you will have lost them.

Sorry to break it to you, but "Don't be Evil" or not, Google is a business, not a charity. They didn't become one of the most successful companies in the world by giving away their search algorithm to the first guy who asked for it.

MrChadMWood
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Chris
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The gclid parameter is encoded in Protocol Buffers, and then in a variant of Base64.

See this guide to decoding the gclid and interpreting it, including an (Apache-licensed) PHP function you can use.

There are basically 3 parameters encoded inside it, one of which is a timestamp. The other 2 as yet are not known.

As far as understanding what these other parameters mean—it may be helpful to compare it to the ei parameter, which is encoded in an extremely similar way (basically Protocol Buffers with the keys stripped out). The ei parameter also has a timestamp, with what seem to be microseconds, and 2 other integers.

andre
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  • +1. 5 Years later and someone thinks to try protobuf. Hopefully someone will figure out how to relate this back to adwords at some point! – Draemon Dec 17 '13 at 00:54
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FYI, I just posted a quick analysis of some glcid data from my sites on this post. There definitely is some structure to the gclid, but it is difficult to decipher.

Draemon
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  • Thanks for the info - nice to know someone else is curious! You really need to decode the characters before looking for patterns, as base64 will spread source bytes over adjacent encoded bytes. I've done similar analysis my self and similarly have convinced myself there's some sort of pattern, but no idea what. – Draemon Apr 20 '09 at 22:32
  • The character analysis is very interesting, and essentially proves that there is data encoded in these gclids... very cool. – ojrac Aug 19 '09 at 19:26
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I think you can get all the goodies linked to the gclid via google's adword api. Specifically, you can query the click performance report.

https://developers.google.com/adwords/api/docs/appendix/reports#click

shep
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  • Yes, this is a new option that Google provides. You can't get very old historical data from this API endpoint though, so it's just good for newer data. – Bani Nov 05 '14 at 16:04
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I've been working on this problem at our company as well. We'd like to be able to get a better sense of what our AdWords are doing but we're frustrated with limitations in Analytics.

Our current solution is to look in the Apache access logs for GET requests using the regex:

.*[?&]gclid=([^$&]*)

If that exists, then we look at the referer string to get the keyword:

.*[?&]q=([^$&]*).*

An alternative option is to change your Apache web log to start logging the __utmz cookie that google sets, which should have a piece for the keyword in utmctr. Google __utmz cookie and you should be able to find plenty of information.

How accurate is the referer string? Not 100%. Firewalls and security appliances will strip it out. But parsing it out yourself does give you more flexibility than Google Analytics. It would be a great feature to send the gclid to AdWords and get data back, but that feature does not look like it's available.

EDIT: Since I wrote this we've also created our own tags that are appended to each destination url as a request parameter. Each tag is just an md5 hash of the text, ad group, and campaign name. We grab it using regex from the access log and look it up in a SQL database.

Jeff Wu
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  • @Jeff Wu I read your answer and, specifically your edit. I wonder how you appended your own request parameters to destination URLs - we have many campaigns already running so, it'd be mighty laborious. For the benefit of others who might wonder the same thing, Google AdWords scripts are one way to do it. Here's a couple of helpful links: [Google documentation](https://developers.google.com/adwords/scripts/) and [Example script adding params to URLs](http://www.freeadwordsscripts.com/2012/12/auto-add-valuetrack-params-to-all.html) – mozz100 Sep 18 '13 at 11:19
  • That's pretty cool, I wasn't aware of that Javascript library when we implemented this. I wrote a Python script to take a CSV of ads and add the tag to each one of the links. Our campaign manager would then take the CSV and upload it to AdWords using the desktop utility. – Jeff Wu Sep 18 '13 at 17:10
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This is a non-programmatic way to decode the GCLID parameter. Chances are you are simply trying to figure out the campaign, ad group, keyword, placement, ad that drove the click and conversion. To do this, you can upload the GCLID into AdWords as a separate conversion type and then segment by conversion type to drill down to the criteria that triggered the conversion. These steps:

  1. In AdWords UI, go to Tools->Conversions->Add conversion with source "Import from clicks"
  2. Visit the AdWords help topic about importing conversions https://support.google.com/adwords/answer/7014069 and create a bulk load file with your GCLID values, assigning the conversions to you new "Import from clicks" conversion type
  3. Upload the conversions into AdWords in Tools->Conversions->Conversion actions (Uploads) on left navigation
  4. Go to campaigns tab, Segment->Conversions->Conversion name
  5. Find your new conversion name in the segment list, this is where the conversion came from. Continue this same process on the ad groups and keywords tab until you know the GCLID originating criteria
TJ Wilkinson
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Looks like my rep is weak, so I'll just post another answer rather than a comment.

This is not an answer, clearly. Just voicing some thoughts.

When you enable auto tagging in Adwords, the gclid params are not added to the destination URLs. Rather they are appended to the destination URLs at run time by the Google click tracking servers. So, one of two things is happening:

  1. The click servers are storing the gclid along with Adwords entity identifiers so that Analytics can later look them up.

  2. The gclid has the entity identifiers encoded in some way so that Analytics can decode them.

From a performance perspective it seems unlikely that Google would implement anything like option 1. Forcing Analytics to "join" the gclid to Adwords IDs seems exceptionally inefficient at scale.

Taylor
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Well, this is no answer, but the approach is similar to how you'd tackle any cryptography problem.

Possibility 1: They're just random, in which case, you're screwed. This is analogous to a one-time pad.

Possibility 2: They "mean" something. In that case, you have to control the environment.

  1. Get a good database of them. Find gclids for your site, and others. Record all times that all clicks occur, and any other potentially useful data
  2. Get cracking! As you have started already, start regressing your collected data against your known, and see if you can find patterns used decrypting techniques
  3. Start scraping random gclid's, and see where they take you.

I wouldn't hold high hope for this to be successful though, but I do wish you luck!

Gregg Lind
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  • Re 1 - I'm pretty convinced they're not random. Our gclids are similar, other people's are similar too, but dissimilar to ours. They're definitely not a simple incrementing id. 2.1 - This is *hard* since there are a lot of gclids you don't see (if they don't click on them). ... – Draemon Dec 13 '08 at 23:11
  • ... I have collected a large list from the logs, and I have identified which bytes change more than others, and my brain shouts "this isn't random" but beyond that nothing has lead anywhere. 2.2/2.3 - I'd love a link to any techniques or tools - instinct hasn't got me very far. – Draemon Dec 13 '08 at 23:14
  • tbh I don't hold out much hope either, but it would be very cool - and I really don't think this is something google should have a monopoly over. I just have a niggling feeling it's "easy if you know how" – Draemon Dec 13 '08 at 23:15
  • http://blog.merjis.com/2007/07/16/click-fraud-google-adwords-and-gclid/ seems to have a lot of discussion about the role of the gclid and googling seems to yield a lot of basic insight. They're new to me, to I'll poke in if I learn more. – Gregg Lind Dec 14 '08 at 15:39
  • Since Google Analytics can understand the gclid, it's likely to be a two-way hash, which is a plus. Work on referrer_id. – Gregg Lind Dec 14 '08 at 15:52
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Here's a thought: Is there a chance the gclid is simply a crytographic hash, a la bit.ly or some other URL shortener?

In which case the contents of the hashed text would be written to a database, and replaced with a unique id.

Afterall, the gclid is shortening a bunch of otherwise long text.

Takes this example: www.example.com?utm_source=google&utm_medium=cpc

Is converted to this: www.example.com?gclid=XDF

just like a URL shortener.

One would need a substitution cipher in order to reverse engineer the cryptographic hash... not as easy task: https://crypto.stackexchange.com/questions/300/reverse-engineering-a-hash

Maybe some deep digging into logs, looking for patterns, etc...

Community
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Jareau Almeyda
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  • No, the gclid definitely isn't a cryptographic hash, as it has terrible entropy (gclids from the same account will be quite similar). . Something is encoded in these gclids, but finding out what or how is another matter altogether. – Draemon Jan 18 '13 at 14:48
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A different approach is to simply look at the referrer data which will at least provide the keyword which was searched.

Ophir Prusak
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I agree with Ophir and Chris. My feeling is that it is purely a serial number / unique click ID, which only opens up its secrets when the Analytics and Adwords systems talk to each other behind the scenes.

Knowing this, I'd recommend looking at the referring URL and pulling as much as possible from this to use in your back end click tracking setup.

For example, I live in NZ, and am using Firefox. This is a search from the Firefox Google toolbar for "stack overflow": http://www.google.co.nz/search?q=stack+overflow&ie=utf-8&oe=utf-8&aq=t&client=firefox-a&rlz=1R1GGLL_en-GB

You can see that: a) im using .NZ domain, b) my keyword "stack+overflow", c) im running firefox.

Finally, if you also stash the full landing page URL, you can store the GCLID, which will tell you the visitor came from paid, whereas if it doesn't have a GCLID, then the user must have come from natural search (if URL tagging is enabled of course).

This would theoretically allow you to then search for the keyword in your campaign, and figure out which adgroup them came from. Knowing the creative would probably be impossible though, unless you split test your landing URLs or tag them somehow.

  • agreed that if the gclid was a genuinely opaque reference, that's the end of it. I'm pretty convinced it has some structure, however. What little information I had from Google seemed to imply this. – Draemon Jan 13 '10 at 23:33