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loupe: A privacy-focused iOS app that raises awareness about what native apps can see

摘要

Loupe 是一个 iOS/iPadOS 应用，通过调用公开的 iOS API，把应用可读取的系统信息原样展示出来，用于让用户直观看到设备指纹是如何被拼出来的。文中解释了这些信号的分层：Passive（无需权限即可访问的系统信息）、Needs Permission（触发系统授权的内容，如定位/照片等）、Advanced（利用 URL scheme 探测、Keychain 持久化等侧信道手段）。应用本身不上传任何数据，所有读取都只在本地展示且不做聚合或哈希处理。同时项目开源（MIT License），代码几乎由 AI 编程工具完成，并支持 iOS 与部分 macOS 构建。作者还提到该项目用于提升对设备指纹与隐私暴露面的认知，并关联推广其隐私浏览器 Psylo。

荐读理由

用 Xcode 26+ 的 buildable folders + swift 快速搭建 loupe 就能获取 iOS 原生 API 真实 fingerprint 值，迁移到项目后直接本地导出 raw 数据，用于验证你的 app 抓取行为，避免跨 app 指纹跟进

原文

Loupe

Loupe

Loupe is an iOS and iPadOS app that gives you a hands-on tour of the device fingerprinting surface. It reads real values from public iOS APIs, the same ones any third-party app can call, and shows them to you raw. The point is simple: see what your iPhone quietly exposes, and why each reading helps an app recognize you again.

Trackers don't need your name, email, or location to recognize you online. Each reading isn't necessarily unique on its own, but together they form a fingerprint that follows you across apps and websites.

Download Loupe on the App Store

Loupe screenshot showing the passive signal category Loupe screenshot showing the needs permission signal category Loupe screenshot showing some highlights from what apps can see

How signals are organized

Loupe groups every reading into three tiers, reflecting the cost of access:

  • Passive — visible to any app with no prompt at all (locale, time zone, screen, battery, and more).

  • Needs Permission — readings that trigger an iOS prompt (contacts, photos, location, calendars).

  • Advanced — clever side-channel uses of public APIs, such as URL-scheme probing via canOpenURL and Keychain persistence across reinstalls.

Privacy

Nothing Loupe reads leaves your device unless you explicitly export it. Values are shown raw, without aggregation or hashing. Nothing is uploaded, synced, or shared.

A note on how this was built

Loupe was written almost entirely by AI coding tools.

Building

You'll need Xcode 26 or newer.

  1. Open code/Loupe.xcodeproj.

  2. Copy code/Config/Signing.local.xcconfig.example to code/Config/Signing.local.xcconfig and fill in your own DEVELOPMENT_TEAM and bundle identifiers. This file is gitignored and never published.

  3. Build and run on a device or simulator.

The project uses Xcode's buildable folders (folder references), so new Swift files are picked up automatically with no need to edit the project file.

macOS

Loupe also builds for macOS. The Mac version is mostly complete, but a few things still need work before it's polished.

Support the project

Loupe is free and open source. If it helped you see what apps can quietly learn about your device, the best way to support more work like this is to try Psylo, our privacy-first browser for iPhone and iPad. Psylo gives you proxy-backed browsing, isolated tabs, and anti-fingerprinting protections.

You can also read why we built Psylo.

License

The source code is released under the MIT License.

The Loupe name and logo, the app icon, all other images and icons, and the design source files are © Mysk, all rights reserved, and are not covered by the MIT license.

About

Loupe is made by Mysk.

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