Converts NSAttributedStrings into HTML (and back)


Carthage Compatible Platforms iOS, macOS Language Swift License Build status Twitter: @mschwarz

Ashton (AttributedStringHTMLTransformation) is an iOS and macOS library for fast conversion of NSAttributedStrings into HTML, and back. Ashton is battle-tested and used in MindNode, for persisting formatted strings.

2.0 Release

The latest release is a complete rewrite in Swift focusing on improved performance and functional backwards compatibility to Ashton 1.x. The new codebase has a comprehensive test suite with a test coverage of > 90% and additional tests against the legacy 1.0 output.

Find out more about the launch of Ashton 2.0 in our Blog Post.

Supported Attributes

The following NSAttributedString.Key attributes are supported, when converting to HTML:

  • .backgroundColor (persisted as RGBA)
  • .foregroundColor (persisted as RGBA)
  • .underlineStyle (single, double, thick)
  • .underlineColor (persisted as RGBA)
  • .strikethroughColor (persisted as RGBA)
  • .strikethroughStyle (single, double, thick)
  • .font
  • .paragraphStyle (text alignment)
  • .baselineOffset
  • NSSuperScript
  • .link

Supported HTML Tags & Attributes

As Ashton supports only tags which are necessary to persist the attributes mentioned above, not all HTML tags are supported when converting HTML --> AttributedString. Basically, Ashton converts an AttributedString into a concatenation of span, p and a tags with style attributes.

Supported HTML Tags:

  • span
  • p
  • a
  • em
  • strong

The following style attribute keys are supported:

  • background-color
  • color
  • text-decoration
  • font
  • text-align
  • vertical-align
  • Additional custom attributes (-cocoa-strikethrough-color, -cocoa-underline-color, -cocoa-baseline-offset, -cocoa-vertical-align, -cocoa-font-postscriptname, -cocoa-underline, -cocoa-strikethrough, -cocoa-fontFeatures)

Colors have to be formatted as rgba like rgba(0, 0, 0, 1.000000).

Integartion with the Swift Package Manager

The Swift Package Manager is a dependency manager integrated with the Swift build system. To learn how to use the Swift Package Manager for your project, please read the official documentation.
To add ZIP Foundation as a dependency, you have to add it to the dependencies of your Package.swift file and refer to that dependency in your target.

// swift-tools-version:5.1
import PackageDescription
let package = Package(
    name: "<Your Product Name>",
    dependencies: [
		.package(url: "", .upToNextMajor(from: "2.0.0"))
    targets: [
		name: "<Your Target Name>",
		dependencies: ["Ashton"]),

After adding the dependency, you can fetch the library with:

$ swift package resolve

Integration with Carthage

Add this line to your Cartfile.

github "IdeasOnCanvas/Ashton"


Encode HTML

let htmlString = Ashton.encode(attributedString)

Decode NSAttributedString

let attributedString = Ashton.decode(htmlString)

Example App

An example app can be found in the /Example directory. It can be used to test NSAttributedString -> HTML -> NSAttributedString roundtrips and also to extract the HTML representation of an `NSAttributedString.


Ashton is brought to you by IdeasOnCanvas GmbH, the creator of MindNode for iOS, macOS & watchOS.


  • Swift Tools 5.1.0
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Last updated: Wed Nov 23 2022 09:01:45 GMT-0500 (GMT-05:00)