Catch common print PDF formatting issues before you submit.
KERF is an independent, browser-based diagnostic utility designed to help self-publishers and book formatters evaluate print-ready files against Amazon KDP and IngramSpark technical specifications prior to upload.
Automated preflight diagnostic for Amazon KDP and IngramSpark specifications. Evaluates document geometry and formatting against explicit rules; does not guarantee third-party platform acceptance.
The Problem
Why Print PDFs Get Rejected
Preparing print files for print-on-demand platforms requires strict adherence to physical geometry. Subtle discrepancies that look fine on a computer screen frequently trigger automated rejections during platform review.
Incorrect Trim Dimensions
Exporting a PDF with default letter or A4 dimensions instead of the intended book trim size (such as 6" × 9" or 5.5" × 8.5") leads to immediate size mismatch errors.
Missing or Incomplete Bleed
Images intended to reach the trimmed paper edge must extend at least 0.125" (9pt) into the bleed area. Gaps or missing bleed margins result in white edge slivers or upload rejections.
Margin & Safe Zone Violations
Text, page numbers, or key design elements placed too close to the binding gutter or outside trim boundary risk being cut off during physical binding and trimming.
Spine Width Miscalculation
Cover spread calculations depend directly on final page counts and specific paper stock caliper. Inaccurate spine dimensions result in misaligned title typography and spine wrapping errors.
Inconsistent PDF Box Geometry
PDF files contain multiple structural boxes (MediaBox, CropBox, BleedBox, TrimBox). Conflicting or shifting box coordinates between pages cause print rip engines to process pages unevenly.
Security & Permission Restrictions
Accidental document passwords or encryption flags that revoke print permissions prevent commercial presses from rasterizing pages. (Detecting permission flags checks document access settings, not the visual DPI of images).
Interface Overview
Diagnostic Inspection Workspace
The planned interface categorizes diagnostic findings by severity, showing what was detected, where it occurred, and practical steps to resolve it.
Inspection Report: interior-manuscript-sample.pdf (192 Pages)
Artwork on pages 42 and 88 terminates at the trim boundary without extending through the required 0.125" bleed margin. This may produce white unprinted slivers upon physical cutting.
CropBox dimensions vary from the defined MediaBox on pages 1–192. Ensure consistent PDF box geometry prior to final upload.
Document satisfies illustrative KDP paperback page count constraints and contains no document-level print restriction flags.
Diagnostic Workflow
How KERF Is Designed to Work
The planned diagnostic workflow is designed to be straightforward and deterministic, evaluating files locally in memory without requiring account creation.
Configure Target Specifications
Select your publishing destination (Amazon KDP or IngramSpark), file kind (interior manuscript or cover spread), trim dimensions, and bleed requirements.
Select & Inspect Your PDF
When a PDF is selected, the in-browser diagnostic engine parses the document structure locally in memory, extracting dimensional facts, box offsets, and layer properties.
Review Diagnostic Findings
Findings are displayed with clear severity categorizations. Each finding identifies what was flagged, which page numbers were affected, and practical steps to resolve the issue in your design software.
Diagnostic Engine Scope
Supported Preflight Categories & Status
We maintain rigorous honesty regarding what our engine checks today versus what is under active testing or planned for future updates.
Implemented & Verified in Test Suite
Validates page width and height against selected trim dimensions, accounting for 0.125" bleed margins.
Evaluates whether background images reach required 0.125" bleed margins on full-bleed pages. Unwraps direct image placements and basic 1-level Form XObjects.
Verifies overall cover spread width based on calculated spine thickness, page count, and paper caliper.
Detects conflicting or shifting MediaBox, CropBox, and TrimBox coordinates across pages.
Flags non-zero PDF /Rotate attributes (e.g. 90° or 270°) that cause print-on-demand RIP engines to misorient pages, while supporting natively dimensioned landscape trim.
Checks interior page counts against platform-specific binding limits (e.g. minimum 24 pages for standard KDP paperback, 18 pages for IngramSpark; maximums vary by binding and paper type).
Detects password protection and encryption dictionaries that cause automated publishing rejections.
Detects encryption dictionary restrictions where printing or high-resolution rasterization permissions are disabled in the PDF metadata. (Does not evaluate the visual resolution or DPI of artwork).
Evaluates runs of blank pages against platform guidelines (such as Amazon KDP's limits on consecutive interior and trailing blank pages), distinguishing potential formatting errors from intentional separators.
Identifies printer marks, color bars, and registration targets that must be removed for print-on-demand submission.
Detects unflattened Optional Content Groups (layers) that can render unpredictably during printing.
Verifies whether book page count meets platform requirements for printing text along the spine (79+ pages for KDP, 48+ pages for IngramSpark).
Under Active Hardening & Verification
Evaluating multi-level transformation matrices and complex nested vector graphics to ensure accurate bleed boundary checks across complex composite artwork.
Planned Future Capabilities
Checking that all fonts used in the interior are fully embedded or subsetted.
Scanning individual raster image placements to flag images under 300 effective DPI.
Verifying CMYK/RGB profile consistency and identifying unseparated spot color swatches.
Verifying that cover spreads leave adequate unprinted margins for platform barcode placement.
Client-Side Inspection: In-Browser Diagnostic Architecture
Book manuscripts represent significant intellectual property. KERF is engineered around a client-side architecture where PDF parsing and preflight checks run locally in your web browser session.
How File Inspection Executes:
- • Local Document Parsing: When you select a PDF, document bytes are processed in browser memory (ArrayBuffer) using client-side libraries to evaluate dimensions, boxes, and metadata.
- • Designed for Local Analysis: Preflight calculations and rule evaluations execute on your device without transmitting document contents to Norticus Software analysis servers.
- • No Manuscript Storage: We do not maintain a cloud document repository, and we do not retain, copy, or index your uploaded manuscripts or cover files.
- • Application Delivery & Future Services: Loading the web application downloads static assets (HTML, CSS, JS) from standard hosting infrastructure. In future releases, account, licensing, or payment flows (if used) will handle transactional metadata separately without uploading your document files.
Target Platforms
Amazon KDP & IngramSpark Requirements
KERF evaluates print files against specifications derived from published submission guidelines for Amazon Kindle Direct Publishing (KDP) and IngramSpark.
Independent Software & Trademark Notice
Amazon, Kindle, and Amazon KDP are trademarks of Amazon.com, Inc. or its affiliates. IngramSpark is a registered trademark of Lightning Source LLC and Ingram Content Group.
KERF is an independent diagnostic software utility developed and published by Norticus Software. It is not affiliated with, authorized, maintained, sponsored, or endorsed by Amazon.com, Inc., Lightning Source LLC, or any of their subsidiaries or affiliates.
Diagnostic Limitations Notice
KERF provides automated diagnostic analysis based on programmatic rule evaluation. A clean preflight report indicates compliance with the specific rules checked by KERF for the selected configuration, but does not constitute a warranty or guarantee of file acceptance by any publishing platform. Final acceptance remains exclusively subject to each platform's proprietary automated preflight checks, manufacturing reviews, and physical printing constraints. This diagnostic does not alter or exclude any non-excludable statutory rights or consumer guarantees that may apply under applicable law.
Questions or Feedback on KERF?
Learn more about our studio approach or contact us with preflight questions.