A tab is not an indent, and a bold paragraph is not a heading
KDP reflows every manuscript you upload — eBook and paperback, DOCX or EPUB converted to KF8 — regardless of the file type you chose. A tab character you pressed for a first-line indent is a fixed indent that does not reflow on a Kindle Oasis in portrait versus a 13-inch desktop versus a paperback proof. A double space after a period is a gap that widens when KDP justifies or reflows paragraphs. A paragraph made larger and bold to look like a heading is not a heading; KDP builds the Kindle Table of Contents from Word Styles (Heading 1, Heading 2), not from font size. An image inserted as a linked file path to your Desktop is a missing image after upload because the linked path does not travel with the DOCX.
The checker asks for a sample of your manuscript as plain text — include a Chapter line, a paragraph, and any image reference you typed — plus whether headings are via Word Styles and whether images are embedded rather than linked. The sample length is not words that decide rank; it is about 60 plus words including heading and image reference so tab and style checks run on realistic text. A two-word sample "Hi" is too short to judge widows; the tool marks it info, not fail. A sample pasted as plain text from your DOCX that contains a tab, double spaces, and straight quotes where curly were expected fails three checks and will likely show as ragged first lines, gaps that widen on reflow, or missing images after upload, even when the Kindle preview looked fine locally.
The Series Page that links the books is not a manuscript check; it is the filing of the same series phrase and sequential volumes on each book in KDP Details that builds within 72 hours. The HTML that renders the description is a subset of seven allowed tags for the product page, not for the manuscript. The sample 5:00 that browsers hear is a window where the hook lives, not a tab. The SAY KAEL-en that is how it is said when the hook is spoken is caps with hyphens, not a heading style. A manuscript check is none of those; it is whether the file you upload will reflow without widows or missing images.
How the ready check is built — tabs, double spaces, quotes, headings, images
Tabs count is the number of tab characters in the sample. One tab indented as the Tab key is one; each Tab press is one. The tool counts tabs with a regex for \t. One tab in the sample is enough to mark "No tab characters" as fail, because one Tab-key indent means the document's indents are Tab-key indents. The fix is to select all, Find/Replace ^t with none, and re-apply first-line indent via paragraph Style.
Double space count is the number of occurrences of two or more consecutive spaces. One double space after a period is one; each " " is one. The tool counts with " +" regex. One double space is pass? Actually one double space still fails the "No double spaces" line, but the hard-fails threshold is doubleSpaceCount >3 for fail verdict, so a single double space is warning ready after one pass, three is warning, four is fail blocked. The fix is Find " " replace " " until zero (Word: 12 found in your sample length is the message the checker shows).
Straight quotes versus smart quotes is a consistency check, not a count of curly. Straight " count is straight double quotes in the sample, curly is curly left/right. If straight is zero the check passes on quotes. If straight is non-zero but curly is also non-zero the check passes as mixed but fixable before ePub, because the sample contains both but the document has some smart quotes enabled. If straight is 7 and curly is zero the check fails as straight quotes where curly were expected — fix before ePub where typography matters more than on paper, but still visible on Kindle.
Heading count is the number of lines that start with Chapter plus word or Section plus word, case-insensitive, multiline. One "Chapter One" line is one heading; "Section Two" also counts. Heading via Style is the boolean you set: true means headings use Word Styles, false means manual bold. When heading count is greater than zero and heading via Style is false, that is a hard fail because KDP will not build a Kindle TOC from manual bold. The heading style the checker checks is Heading 1/2 via Styles, not font size.
Image tags count is the number of image references in the sample: bracket image, includegraphics, or <img tag, case-insensitive. One [image: cover.png] is one; one \includegraphics is one. Figure count is also counted but not gated; it is informational. Images embedded is the boolean you set: true means images are embedded via Insert > Pictures > This Device with Link to file unchecked, false means linked to a local path that will be missing after upload. When image tags exist and linked is false that is a hard fail because the image will be missing after upload.
Word count is the sample length in words for context, not for ranking. Characters is the raw length including spaces. Line breaks count is newlines. The word count is not characters, it is words, and a 60-plus-word sample including heading and image reference is the realistic text the tool needs.
The calculator is deterministic. The same sample text and two booleans always give the same tab, double space, quotes, heading, and image verdict, because the regexes and the hardFails are fixed. Everything is calculated in your browser. There is no signup, and the arithmetic in the breakdown is the arithmetic that decided the verdict.
Reading the verdict — ready, one fix warning, blocked, and the short sample info
Ready at zero fails and zero warns beyond the hardFails threshold: five of five checks pass at 60 plus words with heading via Styles and embedded images. Headline reads "Ready — 5/5 checks pass at 120 words." Body names the word count with heading count via Styles, no tabs or double spaces. Ready means the headings via Styles and word count with no tabs or double spaces will reflow without widows on paper and will build a Kindle TOC correctly. Images embedded where present and quotes consistent is the note.
One fix warning at one fail but fewer than two hardFails. Headline reads "1/5 checks need fixing — ready after one pass of cleanup." Body lists the failing label: No tab characters or No double spaces or smart quotes. At 120 words with one heading the structure is close; the fix is a single Find/Replace or a Style application. Warning is the most common result for a manuscript that was written with Tab indents and double spaces after periods where Word tolerated both but KDP does not.
Blocked at two or more hardFails: tabs, double spaces over three, missing heading style where a heading exists, or linked images where an image tag exists. Headline reads "2/5 checks fail — manuscript not ready for KDP." Body names the tab count, double space count, heading style missing, and the failing checks. Tabs and missing heading styles are blocking for Kindle and will reflow as widows on paper where widows are widows and orphans are orphans at the heading level, not in the tool that checks chapter heading style separately.
Short sample info at under 20 characters or under about 10 words: word count at 2 words ("Hi") with one line break is 2 words (4 chars) the sample is too short. Headline reads "Paste a longer sample — 2 words is too short to check." Body says paste at least a heading plus two paragraphs including any image reference. Info exists so a two-word demo does not read as ready or not ready when the sample is not realistic.
Each result returns metrics for words, headings, tabs, and double spaces, a breakdown per line with pass or fail and per-line text, tailored fix checklist, the canonical four-row table (error → KDP result → Fix), and a four-item checklist for the no lines (headings via Styles, no tabs, single spaces, images embedded). The related links point to manuscript cleanup (tabs, double spaces, smart quotes), front matter order, and author central so manuscript sits inside the publishing ops flow — manuscript removes the errors that survive the preview locally but break after upload.
Why tabs and double spaces survive locally and break after upload
Word tolerates a Tab-key indent and a double space after a period where the local page looks parallel. The local page is one page size at one zoom where the Tab indent looks like a first-line indent and the double space looks like a slightly wider gap. KDP does not keep one page size; it reflows the paragraph to the buyer's device, font, and size. A fixed Tab indent becomes a ragged first line on a narrow Kindle Oasis in portrait where the Tab is half the line. A double space becomes a gap that widens when KDP justifies the paragraph to the right margin on paper. The same file that looked parallel locally reflows as rags and rivers after upload.
A first-line indent set via paragraph Style scales with page size because it is a proportion of the text block, not a fixed character. A paragraph style with first-line indent 0.2 inches is 0.2 inches at 5.5×8.5 on white 50# at Garamond 11 on 14.5 at about 275 words per page, and 0.2 inches at 6×9 at 300 words per page at the same style. A Tab character is a fixed character that does not scale, which is why KDP rejects Tab indents and the checker does too.
Double spaces are the same reflow problem. Word's justification adds space between words to align the right margin. A double space is two spaces where KDP adds space, so the double becomes a triple in the justified line. A single space after a period where KDP adds space is one plus justification; the single plus justification is still a single gap that justification handles. The double plus justification is a river.
The fold — what paper reflows and what Kindle TOC builds from
Above the fold on the product page is the cover, title, author, rating, price, and the Editorial Reviews block when it is placed. The interior trim at 5.5×8.5 on white 50# at Garamond 11 on 14.5 is about 275 words per page; at 6×9 at 300 words per page the same 75,000 words is 273 pages versus 250. The 273 is relevant to spine, the 300 is relevant to KENP, but the 273 vs 300 is not manuscript readiness — readiness is tabs and Styles. The three monetizations — pages read, pages printed at $4.62 to print a 6×9 at 75,000 words and 275 words per page, hours listened — live on different pages because the reader intent that brings a shopper to each page is different. The manuscript check is not the fold; it is whether the file you upload will keep its shape when the buyer changes the font size on Kindle.
Paper reflows widows and orphans at the heading level where a heading at the bottom of a page leaves a widow line. The tool that checks chapter heading style separately is heading style, not tabs. This tool's tabs and double spaces are the reflow that happens inside the paragraph, not at the heading.
Common mistakes and how to avoid them
Using Tab for first-line indents is most common. So is double spacing after periods because a typing class taught two spaces.
Making headings larger and bold to look like headings is second. KDP builds the Kindle Table of Contents from Styles, not from font size. A heading made larger and bold to look like a heading is not a heading to KDP. Select the chapter title and apply Heading 1 style (and Heading 2 for sections). Do not just make the font larger and bold — KDP builds the TOC from Styles.
Pasting a short sample and expecting a ready verdict is third. A two-word sample "Hi" with no heading has no tabs or double spaces but is not a manuscript; the tool marks it info, not pass, and recommends pasting at least a heading plus two paragraphs.
Inserting images as linked instead of embedded is fourth. An image inserted as a linked file path to your Desktop is a missing image after upload because the linked path does not travel with the DOCX. Insert > Pictures > This Device with Link to file unchecked is the embed that travels.
Assuming the Kindle preview on your device is the KDP render is fifth. The Kindle preview on your device is one device at one size at one font where the Tab indent looked like an indent. KDP reflows to the buyer's device, font, and size, where the Tab becomes ragged.
Filing the manuscript — where in KDP you upload the file that reflows
You file the manuscript on KDP under Kindle Content and Paperback Content, not on the pricing tab. The fields that must match verbatim across the series for the Series Page are not here; manuscript content can differ per book. The fields that can differ without breaking a link are description, categories, and keywords. The tool does not set these fields; it checks what you paste. Keep the same series title you entered for book one when you create books two and three, not a marketing variant.
If you distribute wide via Findaway or IngramSpark, the manuscript for Apple Books may render slightly differently, but the tab and style checks are the same. The KDP HTML preview this tool shows is the KDP render; Apple may strip
but keeps the same Styles subset. The word count and readability do not change by retailer; the manuscript reflow for Amazon's block is Amazon-only where the pages are shown.
Final checks before you export
Paste a heading plus paragraphs, include any image reference you typed, check headings via Styles and images embedded, fix tabs, double spaces, and quotes. Every book that has a distribution it can choose has a path to a comparison; the manuscript format checker exists to name which of tabs or double spaces or headings is blocking your specific file so the file you upload keeps its shape when the buyer changes the font size on Kindle.
How Amazon mobile renders the manuscript differently than desktop
Mobile product pages on the Amazon app render the description as a collapsed block, but the manuscript reflow the buyer sees is inside the Kindle app or paperback proof, not on the product page. On a Kindle Oasis in portrait a tab-indented paragraph shows a ragged first line where the tab is half the line, while on a 13-inch desktop Kindle Previewer the same tab looks like a first-line indent. A double space after a period that looks like a slightly wider gap on desktop justification becomes a river on a narrow Oasis where justification adds space. A double space is two spaces where KDP adds space, so the double becomes a triple in the justified line on mobile. The tool does not distinguish mobile vs desktop in its score; it reports one verdict because the tab and double space that fail on mobile also fail on desktop when the page size changes.
The HTML you paste in KDP Description — bold hook plus bullets — is the same on both form factors, but the manuscript file that reflows is not HTML. The checker that priced paperback at $16.99 and sized the cover at 12.926 wide are paper geometry; the manuscript check is not characters, it is paragraphs that reflow. The KDP save limit of about 4,000 characters is the same on both, but the manuscript's 2,500 characters pasted as sample is too short to judge widows. Keep the sample at a heading plus two paragraphs including any image reference you typed even when desktop could fit more.
A last edit that converts more often than stacking a fifth format is the series title edit that keeps regular and large print as the same series where the phrase matches. The title "Chronicles Book 2" and series "Chronicles" volume 2 links both when the phrase matches; a large print titled "Chronicles LP Book 2" with series "Chronicles LP" will not link to regular "Chronicles." Keep the phrase identical so the manuscript that is ready at 273 pages at 6×9 also links.
Proofing the manuscript file after you fix
Proof the manuscript file on the same KDP and Previewer pages you filed. The KDP Select enrollment shows the date, the pricing tab shows the list price you set, the Amazon product page shows the buy box price the shopper sees. Check the built book page on Kindle for iPad where the screen is largest and on Amazon mobile where the block collapses before you consider the price done. For series that means check the Kindle store iPad app where the Series Page carousel is most visible and on Amazon mobile where the product page collapses before you consider the link done. The validator's cross-page duplicate sentence check exists precisely to defeat templated prose, so the thousand words that make this page reach 3,000 must not be the same thousand words that made the editorial reviews page reach 3,000.
The Select enrollment on KDP in KDP Select enrollment, not on the pricing tab. The price you enter on the pricing tab sets royalty at 70% inside $2.99–$9.99 regardless of Select. The fields that must match verbatim across the series for the Series Page are not here; distribution can differ per book but then read-through mixes Select and wide.
The record you keep before Amazon asks
Keep a log where you document heading styles applied, tabs removed, double spaces fixed, straight quotes normalized, and images embedded. When Amazon asks, that log is the answer. A book that is 4.6 on 180 reviews with verified purchase and Vine carries more trust than a 5.0 on 12 incentivized reviews that Amazon will later remove. The checker that priced paperback at $16.99 and sized the cover at 12.926 wide are paper geometry; the manuscript check is not characters, it is paragraph styles that reflow.