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Claude Code Internal Analysis

What is the reverse-engineered cli.js artifact?

This page defines the artifact boundary for reverse-engineering how Claude Code works.

cli.js is the readable JavaScript entrypoint extracted from the Linux x64 Bun standalone package for @anthropic-ai/claude-code@2.1.215. It is not the original TypeScript source tree: it is bundled, minified, and paired with JavaScriptCore bytecode in the same Bun module graph.

For day-to-day reading, this repo publishes a derived view claude-code-pkg/src/entrypoints/cli.renamed.js produced by scripts/normalize-cli-js.mjs and scripts/semantic-rename-cli.mjs. It has identical runtime behavior to cli.js but with semantic identifier names recovered from export tables, runtime class names, dispatch handlers, string constants, and call-path property aliases. Source-anchor tables across this wiki reference the renamed view.

Source anchors

Semantic aliasAnchorMeaning
FinalArtifactExtractorTRAILER, MODULE_RECORD_SIZE, FINAL_ROOT_FILESParses the Bun graph in memory and keeps only selected JS files.
BunEntrypointWrapper// @bun @bytecode @bun-cjsBun CommonJS wrapper emitted for the entrypoint.
EmbeddedProductVersionVERSION: "2.1.215", BUILD_TIME: "2026-07-19T00:01:04Z"Embedded product version/build used by version output and runtime metadata.
ExtractedArtifactIdentity20,160,986 bytes, SHA-256 78007444c51f6828a8c122c97d436038c72c035f9149178d0a8ba13e77cda350Identity of the retained Linux x64 cli.js.
RootCommandSurfaceClaude Code - starts an interactive session by defaultUser-facing root command assembled by the full runtime.
ImageProcessorShimrequire("/$bunfs/root/image-processor.node")Thin wrapper around an embedded N-API image module.
AudioCaptureShimrequire("/$bunfs/root/audio-capture.node")Thin wrapper around an embedded N-API audio module.

Artifact stack

flowchart TD
    Npm[wrapper npm package] --> Native[platform native package]
    Native --> Elf[Linux x64 Bun standalone ELF]
    Elf --> BunSection[.bun section]
    BunSection --> Graph[StandaloneModuleGraph]
    Graph --> Cli[src/entrypoints/cli.js]
    Graph --> Image[image-processor.js]
    Graph --> Audio[audio-capture.js]
    Graph --> NativeAddons[embedded .node addons retained locally and gitignored]
    Graph -. not retained .-> Jsc[JavaScriptCore bytecode]

The Bun payload contains five root modules. The final extractor retains the three readable JavaScript files and writes both native addons locally; *.node keeps the native binaries out of Git.

ModuleRole
claude-code-pkg/src/entrypoints/cli.jsThe main bundled runtime: command parsing, TUI, headless runner, tools, sessions, MCP, plugins, agents, auth, models, telemetry, and updates.
claude-code-pkg/image-processor.jsCommonJS shim that refers to /$bunfs/root/image-processor.node.
claude-code-pkg/audio-capture.jsCommonJS shim that refers to /$bunfs/root/audio-capture.node.
claude-code-pkg/image-processor.nodeGitignored Linux x64 N-API image processor extracted from the graph.
claude-code-pkg/audio-capture.nodeGitignored Linux x64 N-API audio capture/playback module extracted from the graph.

What cli.renamed.js owns

Reverse-engineering cli.renamed.js shows it is the central agent runtime rather than a thin argument parser. Confirmed top-level ownership includes:

  • Bun/bootstrap and product-version fast paths.
  • Commander root command, root flags, and utility subcommands.
  • Interactive TUI/session loop and resume picker.
  • Print/headless runner, stream-JSON I/O, SDK transport, and control frames.
  • Prompt/context inputs such as CLAUDE.md, settings, system-prompt flags, output styles, agents, skills, and MCP.
  • Model/provider/auth selection across first-party, Bedrock, Vertex, Foundry, Anthropic AWS, Mantle, and API-key/OAuth paths.
  • Built-in tools, permissions, hooks, MCP, plugins, IDE/Chrome integration, and settings policy.
  • Local JSONL transcripts, resume/continue/fork/rewind, remote sessions, teleport, and Remote Control.
  • Agents, background-by-default subagents, task tools, background sessions, deterministic dynamic workflows, ultrareview, and auto-mode.
  • Accessibility and recovery modes including --ax-screen-reader and --safe-mode.
  • Diagnostics, debug logs, telemetry/traffic gates, native updater, and media native modules.

What it is not

  • It is not clean source with original module names.
  • It is not sourcemap-backed; temporary Bun graph inspection found no serialized sourcemap payload for this build.
  • JavaScriptCore cached bytecode can be dumped for instruction-level research, but bytecode dumps are no longer retained as final artifacts and do not recover the original JavaScript/TypeScript.
  • Minified anchors behind aliases such as TopLevelMain, CommanderRoot, HeadlessRunner, and InteractiveSessionLoop are version-specific. Use them only with exact string/offset anchors.

Created and maintained by Yingting Huang.