ISBN Barcode Generator

Input handling: hyphens, spaces, and any other formatting characters are stripped automatically, leaving only digits and a possible trailing X (case-insensitive), so an ISBN can be pasted in any commonly seen style — with or without hyphens, with or without a leading "ISBN" label. A 10-character result is treated as ISBN-10; a 13-character result is treated as ISBN-13; anything else shows "Enter a valid 10 or 13 character ISBN." ISBN-10 checksum: each of the first 9 digits is multiplied by a weight counting down from 10 to 2, and the 10th character (which may be a digit or the letter X, representing the value 10) is multiplied by 1. A genuine ISBN-10 is valid exactly when this weighted sum is evenly divisible by 11; anything else is rejected as "Invalid ISBN-10 checksum." ISBN-10 to ISBN-13 conversion: the first 9 digits of a valid ISBN-10 (excluding its own check digit) are prefixed with "978" to form a 12-digit body, and a new 13th check digit is calculated using the EAN-13 formula — alternating weights of 1 and 3 across the 12 digits, summed, then (10 − (sum mod 10)) mod 10. Worked example: the well-known ISBN-10 0-306-40615-2 (digits 0306406152) passes the ISBN-10 checksum, and converting its first nine digits (030640615) with a 978 prefix produces the 12-digit body 978030640615, which yields check digit 7 — the valid, real-world ISBN-13 9780306406157. Deliberately corrupting one digit (for example changing the final 2 to a 3) fails the ISBN-10 checksum and is correctly rejected before any conversion is attempted. ISBN-13 checksum: validated directly with the same alternating 1/3-weight formula described above, comparing the calculated 13th digit against the one you typed. A prefix other than 978 or 979 does not block validation or rendering — it only triggers a small "Not a standard Bookland (978/979) prefix" note, since a small number of legitimate non-Bookland EAN-13-style identifiers can exist. Human-readable text and rendering: the resulting 13-digit code is grouped for display as "ISBN XXX-X-XXXXX-XXX-X" (a generic 3-1-5-3-1 split). This grouping is a reasonable default for readability only — real ISBN hyphen placement actually depends on the specific registrant range assigned to a publisher and can only be looked up authoritatively, not derived from the digits alone; the digits and the checksum, which are independently verified, are the part of the output that is guaranteed correct. The barcode itself is drawn using the exact same EAN-13 module tables, quiet zone, and canvas approach as the general Barcode Generator tool.