chatmarkdown-swift

A SwiftUI Markdown rendering library purpose-built for AI chat interfaces. Not a general-purpose CommonMark renderer — a focused tool for the shape of Markdown that LLMs actually produce, with first-class support for token-by-token streaming, copy-friendly code blocks, and theme integration that fits chat-bubble UIs.

The supported syntax subset and streaming semantics are documented in SPEC.md.

Status

Experimental. No semantic versioning, no release tags, no support promise. main is the contract. The library is extracted from a single consumer and evolves in lockstep with it.

Rendered messages support seamless drag-selection across paragraphs, lists, blockquotes, and code blocks — the whole assistant message is one selection target. This is enabled by the default TextKit-backed renderer; see Selecting & copying text for the opt-out.

Installation

.package(url: "https://github.com/hra42/chatmarkdown-swift", branch: "main")

.target(
    name: "YourApp",
    dependencies: [
        .product(name: "ChatMarkdown", package: "chatmarkdown-swift"),
    ]
)

Usage

import SwiftUI
import ChatMarkdown

struct MessageView: View {
    let markdown: String
    let role: MessageRole

    var body: some View {
        ChatMarkdownView(markdown, role: role)
    }
}

Theming

Themes are value-type structs. Built-in presets: .assistant, .user, .pdfLight. Pass a custom theme via .chatMarkdownTheme(_:).

var theme = ChatMarkdownTheme.assistant
theme.linkColor = .pink
theme.linksUnderlined = false

ChatMarkdownView(markdown)
    .chatMarkdownTheme(theme)

Custom code-block style

struct PlainCodeBlockStyle: ChatMarkdownCodeBlockStyle {
    func makeBody(configuration: ChatMarkdownCodeBlockConfiguration) -> some View {
        Text(configuration.code)
            .font(.system(.body, design: .monospaced))
            .padding()
            .background(.gray.opacity(0.15))
    }
}

ChatMarkdownView(markdown)
    .chatMarkdownCodeBlockStyle(PlainCodeBlockStyle())

Selecting & copying text

By default, ChatMarkdownView renders the entire message into a single NSTextView (macOS) or UITextView (iOS, visionOS) so users can drag-select across paragraphs, lists, blockquotes, and code blocks in one motion. No additional modifier is required.

If you need the legacy per-block SwiftUI renderer (for example, for debugging or to interoperate with a custom selection model), opt out per-view:

ChatMarkdownView(markdown)
    .chatMarkdownRenderer(.swiftUI)

On platforms without AppKit/UIKit (e.g. Linux), the SwiftUI renderer is used automatically regardless of the modifier.

Parsing only

If you only need the AST (for example, to drive a custom renderer), use ChatMarkdownDocument directly:

let doc = ChatMarkdownDocument(markdown: "# Hello\n\nWorld")
for block in doc.blocks {
    print(block.contentHash)
}