When to use reference numbers, how to generate them and how to display them.
Services that use this pattern:
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After a meeting with @owenm6 and the GOV.UK Design System team to talk about authenticating user patterns, we've agreed that what's needed to do is ask the community in government about ‘reference numbers’ (as one example to start) to understand:
I still refer teams to the Dropbox Paper guidance on reference numbers when they come to designing / implementing reference numbers.
Copied over below, so it doesn't get lost. It would be great to include some of this in the design system - possibly in the patterns section?
Transaction reference numbers
Guidance on transaction reference numbers, tracking numbers, invite codes.
Note: this guidance applies to system generated reference numbers, not user-generated references. For example: whilst systems should be forgiving of users entering in reference numbers, they should be very strict when accepting users' passwords.
Some services have found that users expect to get a reference number as part of the process, and don't feel they are 'done' until they receive one.
Do you really need a reference number?
Before you decide to design a reference number, ask if users really need one.
If a reference number is necessary, provide a reference that is easy for users to identify, record and quote when needed.
Most users will never need the reference number. But when they do, make sure you've given them a reference that is easy to use.
Make it clear what the reference is for
Don't rely on reference numbers
Referring to reference numbers
Design principles for good reference numbers
Choice of reference numbers
Showing the reference number to the user
Collecting the reference number from the user
Other useful principles
IXDA have a good discussion of reference numbers in the commercial sector.
Examples from GOV.UK
Register to vote
The early prototypes of Register to vote did not provide a reference number at completion. And the majority of test participants asked for a number. Once we added a reference number, test participants specifically mentioned the number as a signal that they had finished, and as something they would want to keep (by copying the page to a document, sending the page to email, or taking a snapshot of the page on their phone, etc.).
Our completion page currently looks like this:
The reference number is the first six characters of a SHA-256 hash encoded to hexadecimal. By taking the first six characters we get about 16 million values (we need about 700,000). Using part of a hash makes it unlikely that an error in one character will produce another valid reference number.
A six character reference number is easy to copy and quote. References will contain only the digits 1 through 9 and the letters A through F, avoiding tricky letters like I, O and L.
Example: the Post Code