Why does Double Metaphone return two codes?

Some spellings have more than one plausible pronunciation depending on the name's language of origin. The primary code captures the most likely reading and the alternate captures a second, so matching is more forgiving.

When are the two codes identical?

When the word has only one reasonable pronunciation. For example "Schmidt" gives XMT for both codes, while "Smith" gives SM0 and XMT.

How do I decide if two words match?

Treat it as a match if any code of word A equals any code of word B. Comparing all four combinations maximises recall while keeping precision reasonable.

Is this more accurate than the original Metaphone?

Generally yes. Double Metaphone handles many more letter combinations and non-English origins (Germanic, Slavic, Spanish, Italian), so it produces fewer missed matches.

What do the symbols mean?

0 (zero) is the "th" sound and X is the "sh"/"ch" sound. Other symbols are ordinary consonants. Each code is truncated to four characters.

Double Metaphone Encoder

What this tool does

Double Metaphone, designed by Lawrence Philips in 2000, is the successor to Metaphone. For each word it returns two phonetic keys — a primary and an alternate — so that names whose pronunciation depends on their language of origin still match. This is the standard choice for serious fuzzy name matching, and it runs entirely in your browser here.

How it works

The algorithm walks the uppercased word, consuming one or more letters at each step and appending symbols to both a primary and a secondary buffer. Most steps append the same symbol to both buffers, but ambiguous letter groups branch:

"W" in a Slavic-looking name  -> F on the alternate, dropped on the primary
"CH" mid-word                 -> X primary, K alternate (Greek/Italian origin)
"GN" after an initial vowel   -> KN primary, N alternate
"SCH"                         -> context-sensitive X / SK
"TH"                          -> 0 (the "th" sound), with name-origin exceptions

It also tracks a “Slavo-Germanic” flag (triggered by W, K, CZ or WITZ) that changes how Z, J, S and W are treated. Both codes are truncated to four characters. When a word has no ambiguity, the two buffers end up identical.

Matching strategy and examples

Two words are considered a phonetic match if any of their codes coincide. “Smith” yields SM0 and XMT, “Schmidt” yields XMT and XMT — they match on XMT, which is the intended behaviour. “Catherine” gives K0RN and KTRN, capturing both the soft-th and hard-t readings. Use Double Metaphone as the blocking key in record linkage and deduplication pipelines, then apply a finer comparison (edit distance, field-by-field scoring) to the candidate pairs it surfaces. Nothing you enter leaves your browser.