Clean a contact list before you import it

Every CRM migration starts the same way. Someone sends over the contacts, and what arrives is three exports stapled together: a spreadsheet from the old system, a few rows a colleague copied out of their inbox, and a tab that somebody clearly maintained by hand. Names in block capitals. Four spellings of the same company. Phone numbers written six different ways, at least two of them missing the leading zero because Excel decided they were numbers.

The temptation is to import it and fix it later. That is almost always the expensive choice. A duplicate that enters a CRM does not sit still: it collects an activity history, gets attached to a deal, receives a campaign email, and by the time anyone notices there are two records for the same person, merging them means choosing which history to lose. Cleaning before the import costs an afternoon. Cleaning after it costs a project.

So the order that works is boring and worth following. Normalise the formatting first, because you cannot spot duplicates while the same person appears as SMITH, Smith and smith. Then deduplicate, on email rather than name, since two people genuinely can share a name and almost nobody shares an inbox. Then look at what is left over, because the rows that fail validation are usually telling you something true about where the data came from. A column of addresses ending in the same typo'd domain is a broken form somewhere, not a list problem.

This applet does the first two steps and shows you the third. It is deliberately not clever about it: predictable rules you can check, rather than a guess about what you probably meant. You can see exactly which rows it merged and why, because the point of a clean list is that you trust it, and you cannot trust a transformation you cannot inspect.

It also runs entirely inside this page. That is not a technical detail when the list you are about to paste is a client's customer database. Uploading personal data to a free web tool is a processing decision with your name on it, and most data protection policies have something to say about it. Here there is nothing to say, because nothing is sent anywhere.

Where an applet stops being the right answer is repetition. If this is a one-off before a migration, a browser tab is genuinely the correct tool and you should close it afterwards feeling nothing. If it is happening every month, between systems that disagree about what a contact is, then the cleaning is a symptom rather than the job, and the thing worth fixing is upstream.