Merge Excel Files

Q: Are my Excel files uploaded?

No. Parsing, merging, persistence, preview, and export run in your browser. File contents do not enter BaseToolbox analytics.

Q: What is the difference between union and intersection append?

Union keeps every matched column seen in any source and leaves missing cells blank. Intersection keeps only columns present unambiguously in every selected source.

Q: Can I join files with duplicate IDs?

Not in this workflow. Duplicate keys are rejected because silently multiplying rows can create misleading totals. Clean or aggregate duplicate IDs first.

Q: Can I restore a merge after refresh?

Normally yes when persistent browser storage is available. Clearing site data, private browsing, or browser storage eviction can remove saved source files.

Merge 2–20 CSV, TSV, or XLSX sources in your browser. Append the union or intersection of matching columns, or full-join files on one reviewed unique key, with schema issues and an export manifest.

Saved sessions

Add 2–20 files. Each file stays in this browser; legacy .xls is not supported.

Private, browser-local file merging

Source files, selected worksheets, keys, merged data, and manifests stay in your browser and are excluded from BaseToolbox analytics. Files use persistent browser storage when available.

Current limitations

The tool supports CSV, TSV, and modern XLSX, but not legacy .xls, macros, or desktop-Excel formula recalculation.
Append matching uses normalized headers and duplicate-header occurrence. Review all missing-column and type-conflict issues before using the result.
Full join deliberately rejects duplicate, missing, or ambiguous keys; it does not guess how duplicate records should be aggregated.
Browser storage may be cleared or reclaimed, and private browsing may not retain imported files or results.

How local spreadsheet merging works

Add and inspect each source

Import up to 20 files and select the exact worksheet from each workbook.

Choose an explicit merge contract

Append a union or intersection of columns, or choose one unique shared key for a full join.

Review issues and export

Inspect output rows, schema issues, and a preview before exporting CSV, XLSX, or the JSON merge manifest.