idml

A pure-Ruby toolkit for Adobe InDesign IDML files: parse, validate, round-trip, compose, and render to PDF.

What it does

• Parse & round-trip — every IDML part is a typed Lutaml::Model class generated from Adobe’s RelaxNG schemas (reference-docs/schemas/): byte-faithful re-serialization with ZIP_STORED mimetype ordering preserved.

• Validate — RelaxNG validation against the committed InDesign 2026 (DOMVersion 21.5) schemas.

• Compose — insert_idml, add_page_from_idml, prefix, import_xml/export_xml (ported from SimpleIDML).

• Render to PDF — a full pure-Ruby layout + paint pipeline (pdfrb): multi-frame threaded stories, justification with word/letter/glyph limits, footnotes (bottom-of-frame with separator rules), anchored objects, tables (row/column banding, per-side cell strokes, merged cells), Bézier shape contours, gradients, text wrap (bounding-box, contour, and inverse modes), paragraph shading/borders/rules, drop caps, bullets & numbering, CJK layout (kinsoku shori, ruby, vertical writing with tate-chu-yoko and rotated Latin, script spacing, line-end punctuation compression), tagged PDF, hyperlinks, bookmarks, PDF/A, and font subsetting.

Install

gem install idml

.indd files are a proprietary binary format — export them to .idml from InDesign first (File → Export), or use InDesign Server for headless automation.

Quick start

require "idml"

# Round-trip a package
pkg  = Idml::Package.new("doc.idml")
spec = pkg.spreads.first

# Render to PDF
Idml.render(package: pkg, to: "doc.pdf")

Requirements

• Ruby >= 3.3 (tested through 4.0 on macOS/Linux/Windows)

Reference material

The reference-docs/ tree carries Adobe’s IDML specification, the Plug-in SDK’s idmltools (behavioral ground truth), and the generated RelaxNG schemas — the attribute authority for every model class.

License

BSD-2-Clause.