GSM-7 / Unicode checker.

GSM-7 is the 7-bit default alphabet from the GSM 03.38 standard. Its basic table covers uppercase and lowercase Latin letters, digits, common punctuation and a small European set. Each basic character occupies one 7-bit unit, so a single SMS holds 160 of them.

A small set of characters — the euro sign and brackets, braces, backslash, tilde, caret and pipe ( € { } [ ] ~ | ^ \ ) — live in the GSM-7 extension table. They are still GSM-7, but each is sent as an escape character plus the character itself, so it counts as two units instead of one.

Any character outside the GSM-7 basic and extension tables. Common culprits are smart or curly quotes, em dashes, the ellipsis character, many accented letters, and every emoji, Arabic, Cyrillic or CJK character. One such character anywhere switches the whole message to double-byte encoding.

SMS uses a single encoding per message. If even one character cannot be represented in GSM-7, the entire message must be sent as UCS-2 so that character survives. That drops the per-segment budget from 160 characters to 70, which is why a stray curly quote can double or triple your segment count.

The segment calculator reports the encoding, segment count and cost for a whole message. This checker goes character by character so you can pinpoint the exact offending characters, replace them and bring the message back to GSM-7. Use them together.