Read the middle
The cheapest improvement available, and it takes about five seconds longer than what most people already do.
How people actually read an address
Shown fifty six characters of unpredictable text, almost everyone reads the first four or five, glances at the end, and accepts it. That is not laziness, it is how reading works. Long random strings get sampled, and the samples people take are the boundaries.
Forgery is designed around that behaviour. Matching a recognisable opening is cheap, matching the middle is not worth the compute, and matching everything is impossible. So the differing characters sit exactly where sampling does not reach.
The exception
The clipboard swapper replaces the whole string rather than resembling it, so a wholesale substitution is caught immediately by checking the first and last several characters. That is the one place on this site where the quick check is the right check, and it applies specifically to what landed in a send field or an address bar after you pasted.
| Situation | Check |
|---|---|
| An address from a list or a message | The middle. A forgery resembles the original. |
| What appeared after you pasted | The ends. A substitution replaces everything. |
| Either, done properly | Paste both strings somewhere that reports an exact match. Human comparison of random characters is unreliable regardless of care. |
Things that are not the problem
- Confusable characters. Base32 as used here excludes visually ambiguous pairs by design, so an address that looks slightly off genuinely is off. This is never a font issue.
- Case. Onion addresses are case insensitive, so mixed case is a formatting choice rather than a different address.
- Length. Always fifty six characters before the suffix. A sixteen character one is from a retired protocol version that stopped resolving years ago, which tells you everything about whatever published it.
The habit that removes the question
Copy rather than retype, always. Every manual transcription is a chance to introduce an error that will look exactly like an attack when it fails, and it costs you the certainty that would have made the comparison unnecessary.