1. Prepare your list
Use a dedicated spreadsheet with a phone header in A1. Format column A as Plain text before importing a CSV so the leading + and international country code survive. Keep your source file unchanged.
E.164 is the least ambiguous input: a +, country code, and subscriber number. The sample CSV uses fictional numbers to show the format; it is not a deliverability test set. If your export also contains names or notes, keep those in your original sheet and match results by a stable record ID.
2. Choose browser or spreadsheet
The browser checker is the quickest route for a one-off list. Preview the inputs, confirm the run, then export the results. For recurring spreadsheet work, install the downloadable Apps Script in Extensions > Apps Script.
Add LOOKUPLAB_API_KEY under Project Settings > Script Properties. Save, reload the sheet, select up to 100 phone rows and choose LookupLab > Check selected phones. Google asks you to authorize the script. The key is available to script editors, so only share editing access with people who should have it.
3. Keep results you can audit
The script reserves columns B:H for valid, line_type, carrier, country, credits_charged, checked_at and status. It writes each completed result immediately and skips rows already containing results. It never runs automatically when a cell changes.
A non-200 response stops the run. Check your account for 401/402 errors or your rate for 429, then inspect the completed rows before retrying. If you deliberately want a fresh check, clear that row's B:H cells first. Repeating a lookup may consume credits again.
4. Read the result before importing
Separate mobile, landline, voip, toll_free and unknown records. A missing carrier can be a coverage gap; it should not silently become a fake phone number. Keep unknown results in a review segment.
A valid number is not proof that it belongs to your customer, that it accepts SMS, or that you have permission to contact it. Preserve your consent and suppression rules when you import enriched records back into a CRM.
A successful base phone check uses 1-3 credits depending on line type. Caller-name requests use 3-5. Read
meta.charged for the actual debit and test a sample before scaling.Written by LookupLab. Updated October 12, 2026. Implementation reference: Google Apps Script HTTP requests.