ISBN Validator and ISBN-10 to ISBN-13 Converter

A free ISBN validator that checks the check digit of an ISBN-10 or ISBN-13 and converts cleanly between the two forms. Paste a code with or without hyphens; the tool detects the length, picks the right algorithm, and tells you whether the check digit is correct. ISBN-10 uses a weighted sum with weights 10 down to 1 taken modulo 11, where a check value of 10 is written as the letter X. ISBN-13 is an EAN-13 barcode, so it uses alternating weights of 1 and 3 taken modulo 10. The result panel shows the detected type, the check digit your input carries, and the check digit the math expects, so a mismatch is easy to read at a glance. Convert an ISBN-10 to ISBN-13 by prepending the 978 Bookland prefix and recomputing, or convert a 978-prefixed ISBN-13 back to ISBN-10. Codes that start with 979 are flagged because they have no ISBN-10 equivalent. Everything runs as plain JavaScript in the page with one-click copy and a shareable link that reopens your exact code. 100 percent client-side, nothing uploaded.