What is the MAX character length of the SubscriberKey field in SFMC All Subscribers.

I know this might sound crazy... But I am posting this question, as I could NOT find the answer to this! Official doc = https://help.salesforce.com/s/articleView?id=sf.mc_es_subscriber_key.htm&type=5

Just FYI, I am doing a POC, where I need to create a Unique-key by joining 2 fields [both email addresses]

  • I did checked tried and successfully created Subscriber with 512 character Subscriber Key [just used this to generate key for testing https://codebeautify.org/random-alphanumeric-generator]

enter image description here

If any one know the answer/link to official answer please post here, so anyone searching will be able to find easily. Additionally any PRO/Cons of using lengthy subscriberKeys

2 Answers 2


So, I think you can put in whatever size string you want and it will accept it, but I did notice that it only appears to store the first 254 characters. You can see this when:

  • inspecting (using devtools on browser) the subscriberkey value in the All Subscribers search in the UI
  • and on API call returns which only show the first 254 characters
  • and when you try to create a new subscriber but use only the first 254 characters, it says that subscriber already exists.
  • and on the Dataview it shows the char limit in official doc as 254 enter image description here

So I think the actual limit is 254, it is just not explicitly stated anywhere. It also will let you put in whatever value you want on submission but then truncate to 254 and store that value.

With that knowledge too, you may also run into issues with a long Subscriberkey as there may be other limitations on other areas that reduce the acceptable key to even lower than 254. So I would proceed with caution on anything beyond 100 or so.

  • Thanks Greg for all the details and sharing additional info and suggestion :) Commented Dec 16, 2022 at 5:39

The MarketingCloud Mobile Push SDK's registration route is restricted to sending 254 characters for the subscriber key

HTTP 400 when sending a 260 char subscriberKey


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