Digital addresses
Error-Resistant Location Codes
How location codes can be designed, and used, to reduce typing and reading mistakes: look-alike characters, blocks, prefixes and verification habits.
Updated 14 October 2026 · 3 min read
Most problems with location codes come from people, not technology: a letter misread, a character dropped, a block swapped. An error-resistant code is one that is designed to make these mistakes less likely, or easier to notice. Users can add their own habits on top.
The common errors
- Look-alike characters. 0 and O, 1 and I or l, 5 and S, 8 and B.
- Transposition. Two characters swapped, such as 3C4D typed as C34D.
- Omission and duplication. A character missed or repeated.
- Case and spacing. Lowercase typed where uppercase is expected, or a space inserted.
- Mishearing. Over the phone, B and D, M and N sound alike.
What designers can do
- Avoid ambiguous characters or accept them interchangeably.
- Use blocks so errors are easier to see and localise.
- Add a prefix that tells the reader the region, so a code in the wrong country stands out.
- Include check characters where the format allows, so that a typo makes the code invalid rather than silently moving it.
- Keep the code short, since fewer characters mean fewer chances for error.
- Normalise input by ignoring case and extra spaces.
What users can do
- Copy and paste whenever possible rather than retyping.
- Read back the code in blocks when speaking, using clear letter names.
- Look it up before relying on it. See how to verify a digital address.
- Send a link along with the code so the receiver can tap instead of typing.
- Add a landmark so a wrong code is obvious.
The role of a country prefix
A prefix is a cheap and effective check. If a code for a delivery in one country begins with the prefix of another, it is almost certainly wrong. UPCS codes begin with a two-letter country prefix for this and for lookup reasons. See UPCS code format explained.
No code is mistake-proof
Even carefully designed codes can be mistyped into another valid code. That is why a visual check on a map matters more than any single design choice. For wider design principles, read what makes a good location code.
Phone-friendly reading
When giving a code aloud, say each block slowly, spell out letters with a simple word where needed, and ask the other person to repeat it. Written down, confirm it with a link or screenshot of the map. See also how to share your location with a courier.
Frequently asked questions
Can a code detect its own typing errors?
Some designs include a check character or structure that makes many typos invalid. Others do not, so a mistyped code may still be valid but point somewhere else.