What is Finnish vowel harmony?

Within a single native Finnish word, back vowels (a, o, u) and front vowels (a-umlaut, o-umlaut, y) cannot coexist. The neutral vowels e and i pair with either group. This is why suffixes come in pairs, such as the inessive -ssa for back-vowel stems and -ssä for front-vowel stems.

Why does e and i not trigger a flag?

The vowels e and i are phonetically neutral and occur freely with both back and front vowels. A word with only e and i, like meri or kivi, takes front-vowel suffixes by convention but never breaks harmony, so the checker treats them as compatible.

Why might a real word get flagged?

Compound words join stems that each obey harmony separately, so syyskuu (syys + kuu) mixes groups legitimately. Many loan words such as olympialaiset also mix vowels. The checker reports the mix so you can judge; it does not declare the word wrong.

How does this help with suffixes?

Knowing a stem's vowel group tells you which suffix variant to use. A back-vowel stem like talo takes -ssa (talossa); a front-vowel stem like metsä takes -ssä (metsässä). The checker labels each word's group to make that choice clear.

Is anything sent to a server?

No. All analysis runs locally in your browser, so your words and text never leave your device. The tool is safe for private drafts and word lists.

Finnish Vowel Harmony Checker

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This tool checks Finnish words for vowel harmony, the rule that governs which vowels — and therefore which suffixes — can appear together in a single word.

How it works

Finnish divides vowels into three groups:

back    : a, o, u
front   : ä, ö, y
neutral : e, i  (compatible with either group)

In a native, non-compound word, back and front vowels cannot mix. The checker scans each word, records whether it contains any back vowel and any front vowel, and flags the word when it contains both. Words with only one group, or only neutral vowels, pass. This matters because suffixes harmonise with the stem: a back stem takes -ssa (talossa) while a front stem takes -ssä (metsässä).

Example

talossa has only back vowels and passes. metsässä has only front vowels and passes. A coined form like taköö mixes a (back) with ö (front) and is flagged as a harmony violation.

Tips and notes

Treat a flag as a prompt, not a verdict. Compound words such as syyskuu (syys + kuu) and many loan words like olympialaiset mix groups on purpose, and each stem inside a compound harmonises on its own. Use the checker to catch typos and to decide which suffix variant a stem needs, and lean on the alphabet reference if you are unsure which letters count as front or back.