ISBN to ASIN API: Convert a Book's ISBN-10 or ISBN-13 to an Amazon ASIN

To convert an ISBN to an Amazon ASIN, call the SellerMagnet /api/amazon-asin-converter endpoint with conversion_direction=ean-to-asin and the ISBN-13 as the asin parameter. An ISBN-10 must be converted to its ISBN-13 form first (prefix 978, recompute the check digit): in this direction the converter sends the value to Keepa as a barcode exactly as given, and a bare 10-digit ISBN-10 is not a valid EAN-13 barcode, so it will not match. The call costs one credit and returns the ASIN, the book's title and its other recorded barcodes.

Why can't I send an ISBN-10 straight to the converter?

On conversion_direction=ean-to-asin, the endpoint sends whatever value you pass straight to Keepa as a barcode lookup, with no digit-count branching at all. ISBN-13 and EAN-13 are the same 13-digit number space (books use the 978/979 EAN prefix), so an ISBN-13 matches the barcode Amazon has on file for that edition. A bare ISBN-10 is a different, 10-digit number; it is not the EAN-13 code stored against the listing, so the lookup simply does not find it. Converting to ISBN-13 first turns the ISBN-10 into the same barcode format the converter actually matches on.

How do I normalise and check an ISBN before calling the API?

The function below strips dashes and spaces, checks the ISBN-10 mod-11 digit or the ISBN-13/EAN mod-10 digit, converts ISBN-10 to ISBN-13 when needed, and only then calls the converter through get_with_retry. get_with_retry and new_session() come from the Python quickstart; a malformed ISBN raises before any request leaves your machine, so a typo never costs a credit.

isbn_to_asin.py - normalise, check, then convert

import re

from retry import get_with_retry
from sellermagnet import ApiError, new_session

MARKETPLACE = "ATVPDKIKX0DER"  # amazon.com


def _digits(raw: str) -> str:
    return re.sub(r"[^0-9Xx]", "", raw)  # drop dashes/spaces; ISBN-10 check digit can be "X"


def _isbn10_to_isbn13(isbn10: str) -> str:
    """Drop the ISBN-10 check digit, prefix 978 and recompute the EAN-13 check digit."""
    body = "978" + isbn10[:-1]
    total = sum(int(d) * (3 if i % 2 else 1) for i, d in enumerate(body))
    check = (10 - total % 10) % 10
    return body + str(check)


def _isbn10_ok(isbn10: str) -> bool:
    if len(isbn10) != 10 or not isbn10[:9].isdigit():
        return False
    total = sum(int(d) * w for d, w in zip(isbn10[:9], range(10, 1, -1)))
    last = isbn10[9].upper()
    total += 10 if last == "X" else (int(last) if last.isdigit() else -1)
    return total % 11 == 0


def _isbn13_ok(isbn13: str) -> bool:
    if len(isbn13) != 13 or not isbn13.isdigit() or isbn13[:3] not in ("978", "979"):
        return False
    total = sum(int(d) * (3 if i % 2 else 1) for i, d in enumerate(isbn13[:-1]))
    return (10 - total % 10) % 10 == int(isbn13[-1])


def normalise_isbn(raw: str) -> str:
    """Accept an ISBN-10 or ISBN-13 with or without dashes/spaces; return a checked ISBN-13.
    Raises ValueError before a credit is spent, instead of paying for a call that will 400."""
    code = _digits(raw)
    if len(code) == 13:
        if not _isbn13_ok(code):
            raise ValueError(f"{raw!r}: bad ISBN-13 check digit")
        return code
    if len(code) == 10:
        if not _isbn10_ok(code):
            raise ValueError(f"{raw!r}: bad ISBN-10 check digit")
        return _isbn10_to_isbn13(code)
    raise ValueError(f"{raw!r}: not a 10 or 13 digit ISBN")


def isbn_to_asin(session, raw_isbn: str, marketplace_id: str = MARKETPLACE) -> dict:
    isbn13 = normalise_isbn(raw_isbn)
    data = get_with_retry(session, "amazon-asin-converter", asin=isbn13,
                           marketplaceId=marketplace_id, conversion_direction="ean-to-asin")
    return {"isbn13": isbn13, "asin": data["asin"], "title": data["productTitle"]}


if __name__ == "__main__":
    session = new_session()
    for raw in ["978-0-306-40615-7", "0-306-40615-2", "9780000000002", "123", "978-0-306-40615-9"]:
        try:
            print(raw, "->", isbn_to_asin(session, raw))
        except (ValueError, ApiError) as exc:
            print(raw, "failed:", exc)

Example output (illustrative ISBN; retry and gate scenarios)

isbn_to_asin: main scenarios, calls= {'amazon-asin-converter': 3}
978-0-306-40615-7 -> {'isbn13': '9780306406157', 'asin': 'B000OZ0NAI', 'title': 'The C Programming Language'}
0-306-40615-2 -> {'isbn13': '9780306406157', 'asin': 'B000OZ0NAI', 'title': 'The C Programming Language'}
9780000000002 failed: 404: Product not found
123 failed: '123': not a 10 or 13 digit ISBN
978-0-306-40615-9 failed: '978-0-306-40615-9': bad ISBN-13 check digit
gate scenario (free 400, not retried): calls= 1 result: ApiError: 400: This endpoint is not available for the requested marketplace
retry scenario (502 then OK): calls= 2 result: {'isbn13': '9780306406157', 'asin': 'B000OZ0NAI', 'title': 'The C Programming Language'}

Trimmed converter response (example values)

{
  "success": true,
  "data": {
    "asin": "B000OZ0NAI",
    "productTitle": "The C Programming Language",
    "eanList": ["9780306406157"],
    "listedSince": "2011-01-01 00:00:00"
  }
}

Which marketplaces does the ISBN converter cover?

The converter shares its marketplace gate with /amazon-product-statistics and the sales estimator: only the 11 Keepa-backed domains. Since 2026-09-19 any other marketplaceId - including Ireland - gets a free 400 before a credit is deducted, instead of silently falling back to amazon.com. For barcodes that are not book identifiers, see the UPC and EAN to ASIN guide; the ASIN converter page lists every supported conversion direction, and more runnable snippets are on the code examples page.

Bottom line: convert an ISBN-10 to ISBN-13 and check its digit locally, then send it to the same converter endpoint used for UPC and EAN barcodes with conversion_direction=ean-to-asin.