# Swift at Apple: Migrating the TrueType Hinting Interpreter

DevFeed: [Swift at Apple: Migrating the TrueType Hinting Interpreter](<https://devfeed.tech/articles/swift-at-apple-migrating-the-truetype-hinting-interpreter-2932.md>)

Original publisher: [Read original article](<https://swift.org/blog/migrating-truetype-hinting-to-swift/>)

Author: Scott Perry

Published: 2026-06-12T10:00:00Z

Content type: article

Language: en

Sources: [Swift.org](<https://devfeed.tech/sources/swift-org.md>)

Topics: [Swift](<https://devfeed.tech/topics/swift.md>), [Font](<https://devfeed.tech/topics/font.md>), [Memory Safety](<https://devfeed.tech/topics/memory-safety.md>), [Security](<https://devfeed.tech/topics/security.md>), [Memory safety verification](<https://devfeed.tech/topics/memory-safety-verification.md>), [Web](<https://devfeed.tech/topics/web.md>), [pdf](<https://devfeed.tech/topics/pdf.md>)

Tags: [apple](<https://devfeed.tech/tags/apple.md>), [applications](<https://devfeed.tech/tags/applications.md>), [code](<https://devfeed.tech/tags/code.md>), [fonts](<https://devfeed.tech/tags/fonts.md>), [memory-safety](<https://devfeed.tech/tags/memory-safety.md>), [performance](<https://devfeed.tech/tags/performance.md>), [security](<https://devfeed.tech/tags/security.md>), [swift](<https://devfeed.tech/tags/swift.md>), [web](<https://devfeed.tech/tags/web.md>)

## AI overview

Apple describes rewriting its TrueType hinting interpreter from C to memory-safe Swift for Fall 2025 releases. The rewrite addresses the security risks of processing untrusted fonts and reportedly improves performance by 13% on average.

## Source excerpt

TrueType is a widely used vector font standard for rendering text in web pages, PDFs, operating systems, and applications. Familiar fonts like Helvetica, Garamond, and Monaco are all built on TrueType outlines. The format specifies a hinting interpreter intended to help outlines rasterize faithfully on low-resolution displays. Modern high-resolution displays enable beautiful typography from outlines alone, but TrueType fonts that need hinting to render legibly remain in use and we continue to support them. Font parsers process data from untrusted sources, making the TrueType hinting interpreter a security-critical attack surface. To make the format more resilient on Apple platforms, we rewrote its hinting interpreter from C to memory-safe Swift for the Fall 2025 releases. In addition to memory safety, we also improved performance: on average, our Swift interpreter runs 13% faster than the C interpreter it replaced. To accompany this post, we've also published the source code of the Swift TrueType hinting interpreter. We hope sharing our experience helps others doing similar work in Swift. TrueType and the hinting engine Apple developed TrueType in the late 1980s and released it with the launch of System 7 in 1991. TrueType was a major breakthrough for the time: it gave font developers enormous control over how glyphs are displayed, with an advanced grid-fitting algorithm and a sophisticated hinting engine built around a special-purpose bytecode interpreter. TrueType did all this on computers that were vastly less powerful than today's, so it had to be extremely well-tuned for performance. Then the internet revolutionized how fonts were used. TrueType became embeddable in PDF files in 1994 and in web pages in 2008, and it remains as relevant as ever. However, these new use cases brought additional risk: TrueType could now be exposed to untrusted fonts from anywhere on the internet. TrueType fonts may contain programs the hinting engine runs through a bytecode interpr