Key takeaways
- A join combines two files side by side on a key — unlike a merge, which stacks rows on top of each other.
- Excel Join is free and open-source (MIT), built in Python with
pandas. - It replaces VLOOKUP / XLOOKUP across an entire file, in one step.
- Four join types: left (default), inner, right, outer.
- It reports how many rows matched — and unmatched rows keep blank lookup values.
To join two Excel files by a matching column, run a free tool called Excel Join, which pulls columns from a lookup table into your main table in one command — the automation of VLOOKUP / XLOOKUP. Match rows on a shared key, choose a left, inner, right, or outer join, and get a report of how many rows matched.
Join vs. VLOOKUP vs. merge — what's the difference?
VLOOKUP looks up one value at a time and is slow and fragile across big files. Merging (stacking) puts files on top of each other — more rows, same columns. A join is different: it matches rows by a key and adds the columns from a second file. That's exactly what you want when you have orders in one file and customer details in another and need them together.
customer_id — each order gains its customer's name and city.How to install the tool (2 minutes)
You need Python 3.9 or newer. Clone the repository and install its dependencies:
git clone https://github.com/Synth88Labs/excel-tool-join.git
cd excel-tool-join
pip install -r requirements.txtGet Excel Join on GitHub (free)
How to join two Excel files — step by step
Step 1 — The VLOOKUP-style left join
Keep every row from your main file and pull in matching columns from the lookup file:
python join_excel.py orders.csv customers.csv --on customer_id -o joined.xlsxEvery order now has its customer's name and city. Orders with no matching
customer keep blank lookup values (just like a VLOOKUP that returns nothing).
Step 2 — Keep only matching rows (inner join)
python join_excel.py orders.csv customers.csv --on customer_id --how innerStep 3 — Different key names, or fewer columns
Use --left-on / --right-on when the key column has different names, and
--columns to bring in only what you need:
python join_excel.py orders.xlsx people.xlsx --left-on cust_id --right-on id --columns nameThe four join types
| Type | Keeps | Use when… |
|---|---|---|
left (default) | Every left row; adds right columns where matched | You want a VLOOKUP — enrich your main file |
inner | Only rows matched in both files | You only care about records that exist in both |
right | Every right row | The lookup file is the one you want complete |
outer | All rows from both files | You want everything, matched or not |
Real work use cases
- Enrich orders — add customer names, regions, or segments from a customer list.
- Add prices or categories — join a product catalog onto a sales file.
- Combine systems — merge exports from two tools on a shared ID.
- Fill in details — attach employee or account info to a transaction log.
- Find non-matches — a left join's blanks reveal keys with no lookup record.
Common mistakes to avoid
- Mismatched key formatting.
"C1"won't match"c1 "or1. Clean and standardize the key column in both files first. - Duplicate keys in the lookup file. If the right file has repeated keys, rows multiply — make sure the lookup key is unique.
- Wrong join type. A left join keeps unmatched rows (with blanks); an inner join drops them. Pick the one that matches your intent.
- Overlapping column names. Columns with the same name in both files get a
_rightsuffix — rename beforehand for cleaner output.
Frequently asked questions
How do I do a VLOOKUP between two Excel files?
Run python join_excel.py main.csv lookup.csv --on key_column. The tool matches rows on
the key and adds the lookup file's columns to your main file — a whole-file VLOOKUP.
What's the difference between join and merge?
A join combines two files side by side by matching a key (more columns). A merge stacks files on top of each other (more rows). Use this tool to join; use the Excel/CSV Merger to stack.
Can the key column have different names in each file?
Yes. Use --left-on and --right-on to specify the key column name in each
file.
What happens to rows that don't match?
In a left join they're kept with blank lookup values. In an inner join they're dropped. The tool reports how many rows matched.
Is Excel Join free?
Yes. It's open-source under the MIT license, free for personal and commercial use. The source is on GitHub.
Do I need Excel installed?
No. It reads and writes files with Python libraries, so it works without Microsoft Excel installed.
Can I join CSV and Excel files together?
Yes. It reads .csv, .xlsx, and .xls, so you can join any mix.
Summary
VLOOKUP is slow and breaks on big files. Excel Join combines two spreadsheets on a key column in one command — a whole-file VLOOKUP with left, inner, right, and outer joins, plus a match report. It's free, open-source, and works without Excel installed.