CSV Join — Merge Two CSV Files by Key
Join two CSV files locally by exact keys. Choose Left or Inner Join, preserve leading zeroes and reject duplicate lookup keys before exporting complete CSV.
Enabling local controls…
1. Add main and lookup tables
Processed only in this browser. No uploads or storage. Inputs and filenames are not sent to analytics; no tool analytics events are emitted.
Each source: 5 MiB, 20,000 records, 100,000 cells including headers, 200 columns. Nonblank, unique headers and consistent field counts required.
2. Set up the join and preview
Add two sources or load the sample, then press Parse.
Output: up to 20,000 records, 100,000 cells including headers, 200 columns and 16 MiB. Copy limit: 1 MiB; download larger results. UTF-8, comma-separated, CRLF output. Limits reject, never truncate.
Clipboard and manual copy may normalize line endings. Download CSV to preserve original newlines inside fields.
CSV quoting does not neutralize formula injection or prevent spreadsheets changing leading zeroes. Import untrusted data as text and follow spreadsheet security guidance. Values are never silently rewritten.
How to use this tool
Parse main and lookup CSV files, pair 1–3 key columns, select non-key lookup fields and rename conflicts. Join, inspect matched and unmatched records, then copy or download complete UTF-8 CSV.
When not to use it
No fuzzy matching, trimming, automatic type conversion or many-to-many joins. Lookup keys must be unique and nonempty. CSV has no null type; unmatched and matched empty strings export as empty fields. Spreadsheet formula risks remain.
Read the guide →