Why did my Mailchimp audience import skip contacts or create odd fields?

1. Your audience CSV

A contact export from any platform edited in a spreadsheet, or a sheet prepared for Mailchimp's CSV import. Contact data is personal data: this page never uploads it.

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Choose a file or paste the text, then click Check file.

Result

Rows with findings

The rules, and what they leave out

• Identity. Every row needs an Email Address. Emails must be valid and unique; two rows that differ only in capitals are the same contact.
• Default fields. Email Address, First Name, Last Name, Phone Number, Address, Birthday and Tags. Near misses such as Mobile, DOB or Tag are flagged because they can be offered as a new audience field instead. Every other column is treated as an audience field you will map yourself and is only noted.
• Tags. Several tags go in one cell separated by commas, with the whole cell in double quotes. An unquoted comma shifts every later column.
• Excel damage. A Phone Number such as 4.16556E+09 means Excel read the cell as a number and the digits are gone. Format the column as Text before editing.
• Birthday holds a month and a day only, as MM/DD or DD/MM to match the field. A year, or values that mix both orders, are flagged and never rewritten.
• Dates in a column named like a date: one format throughout, ideally YYYY-MM-DD. Mixed or day/month-ambiguous values are flagged and never reordered.
• Safe fixes change only the delimiter, the spelling of default headers and stray spaces around an email, name or phone. It never edits a name, address, tag or custom value, never drops a birthday year, never merges duplicates and never touches a consent or status value.
• Not checked: that Mailchimp will accept the file today, whether an email is deliverable, whether you have permission to message anyone, your audience's existing contacts, unsubscribed and cleaned lists, field limits and size limits, and anything Mailchimp changes in its importer. Import a handful of contacts first.

Common questions

Why did my Mailchimp audience import skip contacts or create odd fields?

The usual causes are a row with no email address, an email that is not valid, the same email on two rows (capitals do not make it different), a header like Mobile, DOB or Tag that is not mapped to the default field and is offered as a new audience field instead, an unquoted comma inside the Tags cell that shifts every later column, a birthday with a year or one that mixes DD/MM and MM/DD, a date column that mixes formats, and an Excel save that turned long phone numbers into scientific notation. This tool tests each of them and names the line.

Does a clean CSV mean I can email these people from Mailchimp?

No. This tool only checks formatting. Permission to market comes from a real opt-in you hold a record of, such as a signup form or a prior platform's subscription list, and Mailchimp asks you to confirm that at import and restricts purchased, rented or scraped lists. The tool never creates or changes consent. Messaging people who did not opt in can breach laws such as CAN-SPAM, GDPR and PECR. Ask a lawyer if unsure.

Why did my phone numbers turn into 4.16556E+09?

Excel treats a long run of digits as a number and shows it in scientific notation; once saved the original digits are lost. The tool flags it but cannot restore them. Re-export from the source with the column formatted as Text.

What does Apply safe fixes change?

Only things with one reasonable reading: the delimiter, the spelling of default headers and stray spaces. Every change is listed with its line. It never edits names, addresses, tags, birthdays or anything about consent.

Is it safe to put my customer list into a web page?

The page runs in your browser, the file is read locally and nothing is uploaded; a test in the code asserts there are no network calls. You remain responsible for how you store and handle the downloaded file.

What does this not check?

Whether Mailchimp will accept the file today, whether emails are deliverable, your existing contacts and field limits. A clean result is not a promise of success: import a few contacts first.