Typo tolerance calculations

Typo tolerance helps users find relevant results even when their search queries contain spelling mistakes or typos, for example, typing phnoe instead of phone. You can configure the typo tolerance feature for each index.

Meilisearch uses a prefix Levenshtein algorithm to determine if a word in a document could be a possible match for a query term.

The number of typos referenced above is roughly equivalent to Levenshtein distance. The Levenshtein distance between two words M and P can be thought of as "the minimum cost of transforming M into P" by performing the following elementary operations on M:

• substitution of a character (for example, kitten → sitten)
• insertion of a character (for example, siting → sitting)
• deletion of a character (for example, saturday → satuday)

By default, Meilisearch uses the following rules for matching documents. Note that these rules are by word and not for the whole query string.

• If the query word is between 1 and 4 characters, no typo is allowed. Only documents that contain words that start with or are of the same length with this query word are considered valid
• If the query word is between 5 and 8 characters, one typo is allowed. Documents that contain words that match with one typo are retained for the next steps.
• If the query word contains more than 8 characters, we accept a maximum of two typos

This means that saturday which is 7 characters long, uses the second rule and matches every document containing one typo. For example:

• saturday is accepted because it is the same word
• satuday is accepted because it contains one typo
• sutuday is not accepted because it contains two typos
• caturday is not accepted because it contains two typos (as explained above, a typo on the first letter of a word is treated as two typos)

The typo ranking rule sorts search results by increasing number of typos on matched query words. Documents with 0 typos will rank highest, followed by those with 1 and then 2 typos.

The presence or absence of the typo ranking rule has no impact on the typo tolerance setting. However, disabling the typo tolerance setting effectively also disables the typo ranking rule. This is because all returned documents will contain 0 typos.

To summarize:

• Typo tolerance affects how lenient Meilisearch is when matching documents
• The typo ranking rule affects how Meilisearch sorts its results
• Disabling typo tolerance also disables typo