CSV Join & Merge — Key-Based Horizontal Joins and Vertical Appends in Your Browser

2025.11.12
Inputs A / B
A

Or paste below
Delimiter:
B

Or paste below
Delimiter:
Mode
Horizontal Join Options
Keys A: Keys B (blank = same as A):
Join type: Duplicate keys in B:
Same-name column conflict:
Key normalization:
Output Output delimiter:

* Keys can be "1-based column numbers" or "header names". Use commas for multiple keys. Examples: ID,Date / 1,3

How to use (3 quick steps)

  1. Load CSV A and CSV B
  • Upload files or paste CSV text into the A/B boxes.
  • Pick the correct delimiter for each (Comma / Tab / Semicolon / Pipe).
  • Check “First row is header” if your CSVs have headers.
  1. Choose a mode
  • Horizontal join (key-based, VLOOKUP alternative):
    • Keys A / Keys B: specify by 1-based index (e.g., 1,3) or header names (e.g., ID,Date). You can mix numbers and names.
    • Join type: INNER (match only), LEFT (keep all A), RIGHT (keep all B), OUTER (keep all A & B).
    • Duplicates in B: use first or last occurrence when B has repeated keys.
    • Same-name columns: add “B:” prefix to B columns, or prefer A, or prefer B.
    • Key normalization: trim spaces, collapse repeated spaces, and/or case-insensitive match.
  • Vertical merge (append):
    • Align by header names (recommended) or by position (column order).
    • Optionally add a “Source” column (A/B) to track provenance.
  1. Run & download
  • Click “Run” to generate a preview (up to ~200 rows shown).
  • Click “Download CSV” to save the full result (UTF-8).

What you get (output)

  • Horizontal join:
    • A single CSV combining A with matching B data per your join type.
    • Multi-key support; duplicate B keys resolved by first/last as selected.
    • Header row is included if you choose “Include header.”
    • Column name conflicts handled per your policy (prefix “B:”, prefer A, or prefer B).
  • Vertical merge:
    • A stacked CSV of A and B.
    • If aligning by headers: union of column names; missing cells are left blank.
    • If aligning by position: rows padded to the longest width.
    • Optional “Source” column (A/B).
  • Delimiter: output uses your selection (Comma / Tab / Semicolon / Pipe).
  • Encoding: UTF-8 (safe for modern tools; import as UTF-8 in Excel).

[Completely Free] Utility Tools & Work Support Tools

You can use practical tools like CSV formatting, PDF conversion, and ZIP renaming entirely in your browser, all for free. Each tool page clearly explains “How to use it”, “What the output looks like”, and “Important notes & caveats”, so even first-time users can start without confusion.

View all free tools

Notes & caveats

  • Keys: numeric indexes are 1-based from the left (1,2,3…); header names must match exactly (before normalization).
  • Normalization scope: trimming/case-folding/whitespace-collapse apply to key comparison only; data cells remain unchanged.
  • Unmatched rows: behavior depends on join type (INNER/LEFT/RIGHT/OUTER).
  • Row shapes: the tool pads rows so the table stays rectangular; missing values become blanks.
  • File size: default per-file limit is 5 MB (configurable with max_mb).
  • Access control: by default, login is required (set require_login=0 to make it public).
  • Encodings: loader auto-detects UTF-8 / SJIS-win (CP932) / EUC-JP / JIS and converts to UTF-8. If characters look wrong, verify delimiter and source encoding.
  • Excel tip: import via “Data → From Text/CSV” and select UTF-8 to avoid garbling.
Copied title and URL