Find what is missing from either list

How it works

1. Load one list into each side. They do not need the same columns or the same row order.
2. Pick the column the two lists have in common.
3. Read the removed count for what is missing from the second list, and the added count for what is missing from the first.
4. Unlock exports if you need to download the result and send it on.

Every row lands in one of five categories

The comparison does not produce a list of differences; it sorts every record on both sides into exactly one of these, using the column you picked as the key. The counts add up to the rows you loaded, so nothing is silently dropped.

Matched

The key appears on both sides and every compared cell is identical. These are the rows you do not have to look at, and on a healthy comparison they are nearly all of them - which is the point, because the job is finding the handful that are not.

Changed

The key appears on both sides but at least one cell differs. Each differing cell is shown with its previous value beside the new one, so the question is never "something moved" but "this figure was 1,240 and is now 1,420".

Added

The key is on the right-hand side only. Usually a genuinely new record, but it is also what a re-keyed identifier looks like: change a reference and the same row leaves as removed and returns as added, which is worth checking before treating a large added count as growth.

Removed

The key is on the left-hand side only. A record that was there last period and is not there now - a leaver, a cancelled line, a row dropped by a filter that was left switched on when the export ran.

Duplicate

The same key appears more than once on one side. This is reported separately rather than folded into the others because a duplicated key makes the comparison ambiguous: there is no single row to compare against, so totals built on that key are unreliable until it is resolved.

Choosing the key column is the one judgement the tool cannot make for you. Pick a column that identifies a record and does not change between the two files - a reference, a code, an ID. Pick something that varies, such as a name or a date, and rows that are really the same record will be reported as one removed and one added.

Questions

How do I find records missing from one of two lists?

Load a list into each side and pick the column they share. Records with no match on the other side are counted as added or removed depending on which list they are missing from, so both directions are answered at once.

Is this easier than using a lookup formula?

A lookup checks one direction, so finding what is missing from both sides means running it twice and reconciling the results by hand. Here both directions come out of a single comparison, along with the records that exist on both sides but differ.

Do the two lists need the same columns?

No. They only need one column in common to match records on. Columns that exist on only one side are reported so you know they were not compared.

Is my file uploaded anywhere?

No. Both files are read and compared inside this browser tab. Nothing is sent to a server, there is no account, and closing the tab discards everything.

What file formats does it accept?

CSV and XLSX. Both sides can be different formats — a CSV against an XLSX works.

How large a file can it handle?

It has been measured on 100,000 rows a side. Large files take a few seconds to parse, and the comparison itself runs in well under a second.

Can I export the differences?

Comparing and reading the result on screen is free. Downloading it as CSV or XLSX is a one-time unlock, and the price is shown beneath the export buttons once you have a result.