Skill

Analyze Claude Code Feature

Reverse engineer a specific feature in Claude Code's source code.

Terminology note: Claude Code's cli.js is minified (whitespace removed, identifiers shortened for size), NOT obfuscated (intentionally made hard to read with control flow flattening, string encryption, etc.). webcrack's --no-deobfuscate flag is used because there is no obfuscation to reverse. The output file is called deobfuscated.js by webcrack convention, but it is more accurately "unminified" source.

IMPORTANT: Use the task list (TaskCreate/TaskUpdate) to track progress through the pipeline. Create all tasks upfront, then work through them sequentially, marking each in_progress when starting and completed when done.

Pipeline

Create these tasks at the start:

1. Acquire source — Extract cli.js from the installed native Bun binary
2. Unminify — Run webcrack + prettier to produce readable source
3. Locate the feature — Search for anchor strings to find the code
4. Extract & annotate — Pull out the feature's code, rename identifiers inline
5. Analyze — Document what the feature does step by step
6. Write report — Produce a markdown report with evidence
7. Self-reflect — Evaluate whether the skill itself should be updated

If the user says to skip steps (e.g., "unminified source already exists at X, skip steps 1-2"), create those tasks as completed immediately.

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Step 1: Acquire source

Run scripts/extract-cli.sh to extract cli.js from the installed native binary. The script caches by version.

bash ~/.claude/skills/analyze-cc-feature/scripts/extract-cli.sh

Important — the source is no longer in the npm package. Since v2.1.113 the npm package (@anthropic-ai/claude-code) is a ~170 KB thin installer; the real CLI ships as a per-platform native Bun standalone executable (~250 MB) with the JavaScript embedded in its module graph. extract-cli.sh locates the installed binary (~/.local/share/claude/versions/<version> or $(which claude)) and runs scripts/extract-bun-cli.py to pull cli.js out of the binary's module graph. It also drops the sibling modules (a precompiled Bun bytecode blob and two Rust NAPI addons — image-processor.node, audio-capture.node) into /tmp/claude-code-npm/bun-modules/.

This produces /tmp/claude-code-npm/package/cli.js (~18 MB). See REFERENCE.md for the binary format details if you need to adapt the extractor to a new layout.

Step 2: Unminify

Run scripts/unminify.sh to produce readable source. The script caches the output.

bash ~/.claude/skills/analyze-cc-feature/scripts/unminify.sh

This produces webcrack-output/deobfuscated.js (~965K lines for 2.1.201, well-formatted). Despite the filename, this is unminified code — see terminology note above.

The script runs webcrack with --no-jsx. On today's ~18 MB bundle the JSX-decompile pass takes ~50 min, needs 4 GB+ RAM, and currently emits output Prettier can't reparse. Skipping it costs only verbose createElement(...) + React memo-cache boilerplate (mechanical to read — see the React/Ink section). If you specifically need decompiled JSX for a UI feature, run the JSX pass separately on the extracted module (a few thousand lines) rather than the whole bundle.

Step 3: Locate the feature

Search the unminified source for the feature keyword the user specified. Use multiple anchor strings:

• The command/feature name as a string literal (e.g., "insights", "compact")
• Any known prompts or descriptions associated with the feature
• querySource: values that tag API calls
• Known field names, labels, or HTML content
• Telemetry event names (e.g., "tengu_compact", "tengu_input_command")

Use Grep to find all occurrences and identify the line range where the feature's code is concentrated. Search for at least 3-4 different anchor strings to triangulate.

Step 4: Extract & annotate

Read the identified line range from the unminified file. Read in large chunks (500+ lines) to see full boundaries. Also search for any helper functions called from within the range that are defined elsewhere (API call wrappers, model selectors, data loaders, prompt builders).

Save an annotated file as {feature}-annotated.js (or {feature}-raw.js + {feature}-clean.js if producing both raw and renamed versions) that contains:

• The extracted code with mangled identifiers renamed inline to meaningful names
• Comments explaining non-obvious logic
• Line references back to deobfuscated.js (e.g., // deobfuscated.js:554320)

Renaming technique:

• Function names: infer from string literals in return values, object properties, error messages
• Parameters: infer from how they're used (e.g., parameter passed to .filter() is likely an item)
• Variables: infer from what they hold (e.g., variable set to new Map() and used with .get()/.set() with session IDs is a session map)

Rules:

• Only rename what is unambiguous
• Flag uncertain renames with /* uncertain */ comments
• Never rename inside string literals, template literals, or regex patterns
• Multi-character identifiers (function names, module vars) are safe for global replace
• Single-character identifiers must be renamed within function scope only
• Avoid renaming $ or _ in functions with template literals (conflicts with ${...})
• Use the Mangled identifier reference table in REFERENCE.md to recognize known infrastructure functions

Scoping strategy: Find the v(() => { ... }) lazy initializer that sets up the feature's module. All functions between this initializer and the next one belong to the same module. For local-jsx commands, also trace the load: → module → call export chain to find the entry-point component, then include all components it renders.

Step 5: Analyze

Read the annotated code and document:

• What the feature does, step by step
• What LLM calls it makes (model, prompts, token limits)
• What data it reads and writes
• Any caching or privacy mechanisms
• Cross-reference against actual output if available (run the feature first)

Step 6: Report

Produce a markdown report with:

• Model and cost metadata at the top (model used, estimated API cost, date, source)
• Architecture overview (Mermaid diagram if helpful)
• Pipeline stages with code excerpts from the annotated file
• Tables for any taxonomies, enums, or mappings
• Findings about behavior, edge cases, interesting details
• All claims backed by specific code evidence (cite as deobfuscated.js:NNNNN)

Step 7: Self-reflect

After completing the analysis, evaluate the skill itself (this file + REFERENCE.md):

1. Were there patterns or infrastructure functions discovered during this analysis that should be added to the Common Patterns table or REFERENCE.md? For example, new helper functions, new command types, new telemetry patterns.
2. Did the pipeline steps feel right, or was anything wasteful/missing? For example, if a step was skipped because it didn't add value, or if a missing step would have helped.
3. Was the scoping strategy effective? Did the lazy-init boundary approach correctly identify the module boundaries?

If improvements are warranted, propose specific edits to this SKILL.md or REFERENCE.md and ask the user if they'd like to apply them. Not every analysis will produce skill updates — only suggest changes when they'd concretely help future analyses.

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Command types

Commands have different type values that affect how to analyze them:

• type: "prompt" — Injects a prompt into the conversation. Look for getPromptForCommand. These are pipeline-style features (like /insights) with procedural logic.
• type: "local" — Runs code locally without sending a prompt to the LLM. The module exports { call: entryFunction } which is invoked directly. The return value determines what happens (e.g., type: "compact" replaces the entire conversation). Examples: /compact, /clear, /copy.
• type: "local-jsx" — Renders a React/Ink UI component. Look for load: which returns a module with a call export. These are UI-heavy features (like /usage) built as component trees.

For local-jsx commands, the extraction strategy differs — see the React/Ink section below.

How commands are dispatched

The dispatch function (mangled name changes per version) matches on command.type:

• "local" — Calls (await command.load()).call(args, toolUseContext) and handles the return type ("compact", "skip", or plain value)
• "local-jsx" — Same load pattern, but the result is rendered as JSX
• "prompt" — Calls command.getPromptForCommand(args, context) and injects the result as messages

New field to expect (2.1.201): thinClientDispatch. Command objects now carry a thinClientDispatch tag ("post-text", "control-request", …) that routes the command when the session is being driven by a thin client / remote control instead of the local TUI. "control-request" commands (e.g. /context, /usage) can be answered by the remote side via a control request rather than local execution. Many former built-in commands are now skills loaded from SKILL.md files (e.g. /code-review, /simplify), so if you can't find a command in the built-in registry, check the bundled/loaded skills.

React/Ink components

Many features render UI using React (via Ink for terminal). Key patterns:

• q1(N) + Symbol.for("react.memo_cache_sentinel") — React Compiler memoization boilerplate. This is verbose but mechanical: it caches JSX elements to avoid re-renders. When reading, mentally skip the cache check/set pattern and focus on what's being created (createElement calls, props, children).
• Component boundaries — A module's components are grouped between consecutive v(() => { ... }) lazy initializers. All functions between two initializers typically belong to the same module.
• Read larger chunks — React components with memoization are verbose but low-density. Read 500+ lines at a time instead of 80–200 to see full component boundaries efficiently.
• createElement(f, { dimColor: true }, ...) — f is Ink's <Text> component. I is Ink's <Box> (layout container).

Common patterns

See the Mangled identifier reference table in REFERENCE.md for the full list of known infrastructure functions (telemetry, settings, token counting, hooks, etc.) with their call signatures and stable evidence patterns for re-identification across versions.

Important notes

• String literals survive minification perfectly. They are the primary evidence for understanding what code does. Prompts, error messages, event names, field names — all intact.
• The querySource field in API call options tags which feature is making the call.
• The v(() => { ... }) pattern is a lazy initializer — code inside runs once on first access.
• Look for command definitions: objects with type: "prompt", name, description, getPromptForCommand, or type: "local-jsx" / type: "local" with load:.
• For local-jsx commands, trace the load: function to find the module, then find its call export to locate the entry point.
• Cite line numbers in all analysis artifacts as deobfuscated.js:NNNNN for traceability.