1. Run a probe
A probe is an experiment anyone can run: turn on airplane mode, force-quit the app, use a second device. No tools needed.
The App Teardown Handbook
Mobile system design, read from the outside. Use an app, run a few simple experiments on it, and work out the design behind it. Any app, any store, any scale, any technology.
How it works
Section titled “How it works”Every mobile app is built under the same constraints: an unreliable network, a process the operating system can end at any time, a limited battery, a release that cannot be recalled, and a client the backend cannot trust. Those constraints leave only a few workable designs for each problem, and each design behaves differently in ways you can see.
2. Read the signal
Pick what you saw. The handbook tells you which design produces that behavior, and how sure you can be.
3. Record the teardown
Your results fill in a worksheet for that app, which you can export and keep.
4. Sketch the backend
Each client design needs specific backend support, so a client teardown also gives you the backend.
Where to go
Section titled “Where to go”ContentsAll 55 chapters and the question each one answers.
Signal lookupDescribe a behavior you saw and find the designs behind it.
Teardown worksheetRecord an app's design, probe by probe, and export it.
GlossaryEvery term, with one meaning each.
Worked example: BlueskyA real teardown, checked against the app's public source code.
Worked example: ExpensifyAn offline-first app, and the three readings the method got wrong.
Worked example: JoplinA local-first notes app, 53 probes, and the nine readings the method got wrong.
What the handbook covers
Section titled “What the handbook covers”- Part I. The teardown method. The constraints, a model of any app, the probes, and how to turn a signal into a design claim.
- Part II. Concerns. One chapter for each aspect of system design, from startup and sync to payments and releases.
- Part III. Archetypes. Complete teardowns of app types such as messaging, feeds and ride-hailing, each with notes on how it is asked in a design interview.
The handbook is independent of platform and framework. Logic is shown as neutral pseudocode and diagrams.