Check Sideline Registration
Confirm whether phone numbers are registered on Sideline before building outreach to North American business users.
Upload up to 1 million numbers per batch and complete a full screening in about 3 minutes to quickly confirm whether numbers have an active Sideline account.
Capability Track
phone-list.txt
+44 7……2484
+62 8……9017
+55 1……6723
√ One number per line in TXT
Valid filtering accuracy ≥98%
Average speed: 3 min / 1M records
Export TXT/CSV/Excel
Sideline Validity Check
Sideline Number Check
Capabilities
What can GeekNums check on Sideline?
Registration status
Confirm whether a phone number is registered with Sideline (yes/no), helping you filter out unregistered numbers before marketing.
Number status
RegisteredNot registered
Passive checks, invisible to users
Only reads the Sideline registration signal; never sends messages, attempts logins or triggers notifications to the target account.
Check
4 Steps
Bulk-check Sideline in just 4 steps
Use case: find out which numbers are on Sideline.
Generate Numbers
Use the number generator to create numbers for your target region (or upload your own numbers directly).
Upload Numbers
TXT/CSV/Excel supported, up to 1 million records per upload.
Two-layer Validity Check
1. Check the number really exists
2. Check whether it's linked to a Sideline account
Export Results
Download the completed file and export every filtered result in bulk.
Q&A
FAQ
Yes. Upload up to a million numbers as TXT/CSV/Excel or call the REST API, then download a file with each number's registered/not registered result. You're only charged for successful checks.
North American numbers are very well supported. Checks accurately identify second numbers assigned by Sideline as well as the real primary number network behind them, helping separate genuine business users from dead marketing numbers.
Yes. New accounts get $5 in trial credits on sign-up, no credit card required; after that, every Sideline check is pay-as-you-go with no monthly fee.
