apk-reverse/README.md

apk-reverse

An Agent Skill for Android APK reverse engineering, debloating, ad removal, surgical dex patching, repacking, and runtime/server analysis.

It is a skill, not a tutorial: it is written to be loaded by an agent (Claude Code, Codex, or any harness that supports the Agent Skills format) while it works, so it is organized for progressive disclosure — a short decision-oriented SKILL.md, detailed references loaded only when a step needs them, and parameterized scripts you can run directly.

What it is good at

• Deciding fast whether a request is even achievable client-side, instead of burning hours on a paywall that is enforced by a server.
• Deciding what form the deliverable must take before any work starts — an unrooted, self-contained artifact is a different problem from "make it work on this machine", and confusing the two is the most expensive drift in this domain.
• Choosing the safest patch layer for a given change, and avoiding the layers that break the app.
• Catching the repack failure that looks like success: an app that installs, launches and renders perfectly while every signed request is rejected, because the client derives its request-signing key from its own signing certificate.
• Separating your own mistakes from the app's or the server's problems — a feature-scoped failure (login, registration, payment) is often a TLS/certificate issue on one code path, not a consequence of the patch you just built. Device state, a dead device server and clock drift masquerade the same way.
• Establishing which architecture and which library are actually executing, rather than trusting what the manifest ships or what the device claims.
• Working through packed/hardened targets: identifying the packer, unpacking, and turning a memory dump back into a patched, installable APK.
• Keeping a long task honest: a live record, graded conclusions, calibrated timeouts, and bounded waits, so progress is not lost and the same mistake is not made twice.
• Avoiding the specific mistakes that produce an APK that builds perfectly and dies at runtime.

Structure

SKILL.md                  decision tree, workflow, hard constraints, indexes
references/               loaded on demand, one topic each
  recon.md                    identify packer, SDKs, code location, tamper checks; unpacking
  packers.md                  hardened targets: rejection signals, measuring the validation
                              boundary with single-variable tests, choosing a native host
  framework-runtimes.md       Flutter / React Native / Unity: which layer owns the UI, and how to
                              find logic when there are no symbols (string encoding traps)
  dart-aot.md                 Dart AOT in depth: version pinning and building a matching decompiler,
                              the object pool and reference indexes, register/boolean conventions,
                              the three signatures that identify business logic, locating, patching
  native-and-so.md            .so hosts, DT_NEEDED vs JNI_OnLoad, relocation limits,
                              relocation-free bootstrapping, replacing Java methods natively,
                              and which ABI/library is *actually loaded and executing*
  long-task-discipline.md     live record, conclusion grading, drift control, timeout and
                              wait calibration, deliverable-form drift, handover
  ad-removal.md               ad taxonomy, wrapper mapping, callback trap, global gates, verification
  signature-derived-keys.md   when the app's own signing certificate is used as key material:
                              detection greps, why offline extraction is unreliable, the
                              hardcode-then-verify procedure
  membership-and-limits.md    server vs client authority; what is and is not patchable
  server-api.md               probe an app's API; prove who owns the gate
  tls-and-cert.md             feature-scoped network failures: expired certs, dual trust chains
  third-party-builds.md       auditing a "cracked"/"modded" APK before trusting it
  dex-patching.md             patch-layer table + dexlib2 technique in depth
  repack-and-sign.md          repack rules, unpack-and-repack, signing, post-install hazards
  runtime-data.md             DataStore / SharedPreferences / SQLite / protobuf; when the app
                              rewrites your edit, and decoding a value that looks encrypted
  dynamic-frida.md            Frida setup, version pinning, the four-layer probe, hook strategy
  environment.md              device/emulator setup, root, ADB, offline devices, log signals,
                              emulator console control and recovery, preflight, look-at-the-screen
  verification.md             the claim ladder; what "done" means
  pitfalls.md                 the failure catalogue -- read before building
scripts/                  parameterized, path-agnostic
  smtool.py                   baksmali/smali wrapper with a configurable classpath
  dexpatch/                   dexlib2 method-level surgical rewriter (preferred tool)
  patch_smali.py              method-body replacement in a smali tree
  dex_strpatch.py             byte-level string patch with a string_ids ordering guard
  dex_classdiff.py            prove a dex edit was surgical
  dex_strings.py              strings/URLs/SDK markers without a decompiler
  dart_pool_strings.py        recover literals from a Dart AOT snapshot (framed entries, the
                              one-byte vs UTF-16 split, file offsets, run-length noise filter)
  dart_pprefs.py              build/query the object-pool -> code-site index for a Dart snapshot
  dart_disasm.py              annotated windowed disassembly of Dart AOT code + B/BL caller index
  find_refs.py                count callers of a method before patching it
  repack.py                   rebuild APK, strip only signatures, sign, verify
  devsh.py                    quoting-safe ADB shell helper
  usb_net_proxy.py            give an offline device network over USB
  datastore_inject.py         encode/inject AndroidX DataStore preferences safely
  probe_api.py                probe an HTTP API with the right headers
  grab_crash.py               recover stacks hidden by a crash-reporter SDK
  install_test.py             install + launch health check with logcat signal scan
  frida_probe.js              four-layer runtime probe (app net layer + OkHttp + java.net + exceptions)
  run_probe.py                inject the probe, stream it to a log file, stay resident
  tls_check.py                strict certificate check for one or more hosts
  preflight.py                environment check before every experiment block (device, root,
                              ABI/translation, clock skew, leftover proxy/forwards, dead server)
  lib_map.py                  what is *actually mapped* into a live process: per-library path,
                              base, architecture, and whether it came from the APK or was
                              materialized at runtime
  blob_decode.py              search, don't guess, the framing of a stored value
                              (base64/hex x rotation x deflate); re-encode the edited payload
  snap.py                     bounded burst screenshots + control-tree capture with a stall
                              detector, and a verdict on whether the tree is usable at all
  sig_probe.py                find the exact signatures[0].toCharsString() value — offline
                              candidates from an APK, or the authoritative read from a device

Install

Drop this directory where your agent finds skills, e.g.:

<skills-dir>/apk-reverse/SKILL.md

The agent loads SKILL.md when a task matches its description, and pulls in references/* only as needed. No global state, no machine-specific paths.

Requirements

Nothing is mandatory; each script checks what it needs.

Tool	Used for
Python 3.9+	all scripts
baksmali / smali + dexlib2 jars	disassembly, assembly, surgical patching
JDK (javac, java)	building/running the dexlib2 patcher
Android SDK build-tools (aapt, zipalign, apksigner)	manifest info, alignment, signing
uber-apk-signer (optional)	one-step align + sign
ADB	device work
Frida (host package + matching on-device server)	dynamic analysis
a rooted device or emulator	anything beyond static analysis

Read this first

references/pitfalls.md. It is the most valuable file here — every entry is a failure that produced a broken artifact while looking completely healthy.

The three that hurt most:

1. Stripping the whole META-INF/ during a repack deletes ServiceLoader registrations and the app dies at startup with an error that names an unrelated library.
2. Patching a byte-level string without preserving string_ids ordering gets the whole dex rejected, while checksums and signatures verify perfectly.
3. Rebuilding a dex with a whole-tree smali round-trip damages R8 output invisibly — class tables compare clean, and it only blows up at runtime.

Scope

Built for working on your own applications, on samples you are authorized to analyze, and in CTF/competition sandboxes. It contains no vendored third-party binaries and no target-specific data.