For the reader's convenience

When wondering about questions like this, I consult:

• google n-grams, which show that for the reader's convenience is by far the most common of the three expressions

• a large corpus

  • such as the Corpus of Contemporary American English, where reader 's convenience (the space is there because of the way words are separated in the corpus) yields a single result, again in the phrase for the reader's convenience, while reader convenience yields two occurrences of for reader convenience

  • in the iWeb Corpus, a search for * * reader 's convenience yields

    • 31 occurrences of for the reader's convenience
    • 1 occurrence of each of as per reader's convenience, the present reader's convenience, the ordinary reader's convenience, provided for reader's convenience, and for your reader's convenience

    while * * reader convenience gives

    • 11 occurrences of added for reader convenience
    • 9 occurrences of as a reader convenience
    • 3 occurrences of provided for reader convenience as well as # For reader convenience (where # is the beginning of a paragraph or something like that)
    • 2 occurrences of . For reader convenience, are for reader convenience, category for reader convenience, included for reader convenience, pdf for reader convenience, settings for reader convenience
    • 11 other phrases, each of which occurs just once

Based on this, I would go with For the reader's convenience.