Base64 Validator
Check whether a string is valid base64 or base64url and preview what it decodes to.
Runs locally in your browser. Your input is not uploaded.
How to Use
- 1
Paste strings
One per line — standard or URL-safe base64.
- 2
Read the verdicts
Variant, padding, and decoded byte count are reported.
- 3
Check the preview
Text content is shown; binary shows leading hex bytes.
Frequently Asked Questions
- The tool checks the alphabet (A-Z, a-z, 0-9, +/ or -_ for base64url), padding rules, and the length constraint (mod 4 ≠1), then actually decodes it to prove validity.
Related Tools
Email ValidatorValidate email address syntax with detailed feedbackURL ValidatorCheck URL format and parse components for validityIP Address ValidatorValidate IPv4 and IPv6 address formatMAC Address ValidatorValidate MAC address format in multiple notationsUUID ValidatorValidate UUID format and detect version (v1–v5)Credit Card ValidatorValidate credit card numbers with Luhn algorithm (no data sent)Phone Number ValidatorValidate international phone number formatsDomain ValidatorValidate domain name and hostname syntax