mht2webarchive

Small macOS CLI that converts MHT / MHTML files into Safari-compatible .webarchive files.

What It Converts

• MHT / MHTML is a MIME multipart snapshot format: one file contains the main HTML document plus embedded resources such as images, stylesheets, and other referenced assets.
• .webarchive is Apple's archived webpage format used by WebKit and Safari. It stores a main resource together with subresources in a structure Safari can reopen as a self-contained page.
• This tool converts between those models by parsing the multipart MHT payload, decoding each part, resolving archived resource URLs, and re-emitting the result as a WebArchive made of WebResource entries.
• In practice, the goal is format translation rather than visual re-authoring: preserve the captured page and its embedded assets closely enough that Safari can render the archive offline.

Build

swift build

GitHub Actions must use an Xcode 16 / Swift 6 toolchain before building because the package manifest uses // swift-tools-version: 6.0.

Test

swift run mht2webarchiveIntegrationTests

Run

swift run mht2webarchive input.mht
swift run mht2webarchive input.mht -o output.webarchive
cat input.mht | swift run mht2webarchive - -o output.webarchive
cat input.mht | swift run mht2webarchive - -o - > output.webarchive
swift run mht2webarchive --batch inbox/ more.mhtml --output-dir converted

Notes

• Targets macOS and uses WebKit's WebArchive / WebResource types to emit the archive.
• Supports common transfer encodings: base64, quoted-printable, 7bit, 8bit, and binary.
• Resolves relative Content-Location values against the snapshot URL when present.
• Batch mode accepts both individual files and directories, and scans directories recursively for .mht and .mhtml.
• The converter aims for direct format translation: it decodes each archived MIME part and writes the HTML and subresources into the .webarchive without rewriting HTML or synthesizing fallback assets.