Two source trees, two access strategies. AOSP lives on android.googlesource.com (Gitiles); AndroidX lives on GitHub. cs.android.com blocks automated fetching — it's a human-browse JS SPA only (never WebFetch it).
Preferred: the android-sources MCP
If mcp__android-sources__* tools are available, always prefer them over WebFetch/gh — local source, sub-10ms lookups:
| Goal | MCP tool |
|---|---|
| Find a class by name/pattern | search_classes (glob, e.g. *ViewModel*) |
| Read full class / a method / its members | lookup_class / lookup_method / list_class_members |
| Class hierarchy | get_class_hierarchy |
| Search text/regex across sources | search_in_source |
| List AndroidX artifact versions | list_available_versions |
| Definition / references / type info (LSP) | goto_definition / find_references / get_type_info |
Fall back to the WebFetch/gh strategies below only when the MCP tools aren't available.
Fallback: WebFetch + gh
AOSP (framework internals, @hide APIs, internal constants, default attr values) → Gitiles. Raw text is base64-encoded and smaller:
https://android.googlesource.com/platform/frameworks/base/+/refs/heads/main/{path}?format=TEXT
Use refs/heads/main (the active default branch), or a tag like android-14.0.0_r74 for a specific API level. Key repos: platform/frameworks/base (core/java/android/ → View/Activity/Context; services/core/java/ → system services; core/res/ → default attrs/styles), platform/libcore (ojluni/src/main/java/ → Java core).
AndroidX (androidx.* source + samples) → GitHub. File content via raw.githubusercontent.com; directory listings via gh api:
https://raw.githubusercontent.com/androidx/androidx/androidx-main/{path}
gh api repos/androidx/androidx/contents/{path} --jq '.[].name'
Samples live next to the source as {ClassName}Samples.kt under a samples/ subpath. Key path prefixes: Compose UI compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/, Foundation compose/foundation/foundation/src/commonMain/kotlin/, Animation compose/animation/animation/src/commonMain/kotlin/. AndroidX is mirrored on Gitiles (platform/frameworks/support, androidx-main), but the GitHub layout is the canonical, better-documented path for androidx.* — prefer it.
When the path is unknown
Use cs.android.com as a human search UI (not WebFetch — JS SPA) to locate the class/file, then fetch via Gitiles (AOSP) or raw.githubusercontent.com / gh api (AndroidX):
https://cs.android.com/search?q=ClassName+methodName&ss=android # &ss=androidx for AndroidX
Both trees change frequently — always fetch current source rather than trusting remembered line numbers.