Why this tool is useful
Use this tool to identify a shared literal fragment in filenames, identifiers, snippets or compact sequence data where gaps must break a match.
Text & List Tools · runs locally
Longest Common Substring Finder
Locate the longest uninterrupted run of Unicode graphemes that appears identically inside both supplied texts.
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How it works
A rolling dynamic-programming row resets mismatches to zero and tracks the best ending position, keeping memory bounded while returning the exact fragment.
Practical example
ABABC and BABCA contain the uninterrupted substring BABC, which has length 4.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.