# Code Trace

> Trace code flow

- Skill: `laststance/code-trace` (Agent Skill, multi-file: 8 files)
- Install (CLI): `npx skillmds@latest add laststance/code-trace`
- Raw SKILL.md: https://api.skillmd.com/api/skills/laststance/code-trace/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: laststance (https://skillmd.com/u/laststance)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/laststance/code-trace

---


## Codex Compatibility
When running this skill in Codex, translate Claude Code-only primitives before acting: `AskUserQuestion` -> chat/request_user_input, `TodoWrite` -> `update_plan`, `Task`/`TaskCreate`/`TeamCreate`/`SendMessage` -> `spawn_agent`/`send_input`/`wait_agent` when available and allowed, and `EnterPlanMode`/`ExitPlanMode` -> a concise chat plan plus explicit approval.
Resolve `Read`/`Write`/`Edit`/`Bash`/`WebSearch`/`WebFetch` to Codex file/shell/web tools, and map `~/.claude/...` paths to `~/.agents/...` or `~/.codex/...` unless the task explicitly targets Claude Code.

## Cursor Compatibility
When running this skill in Cursor Agent, translate Claude Code-only primitives before acting: `AskUserQuestion` -> `AskQuestion`; `TodoWrite` -> Cursor `TodoWrite` or an equivalent checklist; `Task`/`TaskCreate`/`TeamCreate`/`SendMessage`/multi-agent flows -> Cursor `Task` (subagents), parallel Tasks, or `run_in_background` when allowed (`TeamCreate`/`SendMessage` may have no exact match); `EnterPlanMode`/`ExitPlanMode` -> Plan mode (`SwitchMode` / `CreatePlan`) plus explicit user approval.
Resolve `Read`/`Write`/`Edit`/`StrReplace`/`Bash`/web/search/MCP via Cursor Composer or Agent equivalents. MCP names written as `mcp__server__tool` typically map to `call_mcp_tool` with configured server identifiers. Map `~/.claude/...` to `~/.cursor/skills/`, `.cursor/skills/`, and `.cursor/rules/` unless the task explicitly targets Claude Code.


<essential_principles>
## How Code Tracing Works

This skill traces code execution paths interactively, letting you navigate through the codebase
like a debugger stepping through code - but with rich explanations at each step.

### Principle 1: Application Boundary

Trace ONLY application code. External dependencies (node_modules, vendor/) receive:
- A summary of what they do
- Link to official documentation
- NOT deep-traced into their internals

**Why**: External libraries can be 100K+ lines. Tracing into them wastes context and obscures
the actual application logic. The goal is understanding YOUR code, not library internals.

### Principle 2: Interactive Navigation

Every conditional branch becomes a user choice:

| Code Pattern | Presentation |
|--------------|--------------|
| `if/else` | "Path A: condition true" vs "Path B: condition false" |
| `switch` | One choice per case |
| `try/catch` | "Success path" vs "Error path" |
| `async/await` | Option to trace into called functions |

**Why**: Linear traces miss important paths. Interactive navigation lets users explore
exactly what they're interested in.

### Principle 3: Progressive Explanation

Each step includes:
1. **Location**: File + line range + function name
2. **Code**: Full source (no abbreviation)
3. **What**: Brief summary of what the code does
4. **Why**: Why this step exists in the flow
5. **Next**: What happens next (or choices if branching)

Use thinking markers (🤔🎯⚡📊💡🔐) for clarity.

### Principle 4: State Persistence

Trace state is stored in Serena Memory to enable:
- Resuming interrupted traces
- Backtracking to previous decision points
- Saving completed traces for future reference
</essential_principles>

<intake>
## What would you like to trace?

1. **Trace a request flow** - Follow HTTP request from receipt to response
2. **Trace a function call** - Follow a specific function through the codebase
3. **Resume previous trace** - Continue from where you left off

Please provide additional context:
- For request tracing: Which endpoint? (e.g., "POST /api/users")
- For function tracing: Which function? (e.g., "validateUser" or "src/utils/auth.ts:checkToken")

**Wait for response before proceeding.**
</intake>

<routing>
| Response | Workflow |
|----------|----------|
| 1, "request", "HTTP", "route", "API", "endpoint", "POST", "GET" | `workflows/trace-request.md` |
| 2, "function", "call", specific function name | `workflows/trace-function.md` |
| 3, "resume", "continue", "previous" | Read Serena memory for `trace_session_*` |

## Before Starting Any Workflow

1. **Detect Framework**: Run `scripts/detect-framework.sh` to identify:
   - Express, Next.js (App/Pages), Fastify, Hono, NestJS, Koa, or generic

2. **Load Framework Patterns**: Read `references/framework-patterns.md` section for detected framework

3. **Prepare Serena**: Ensure Serena MCP is available for:
   - `find_symbol()` - Locate functions/handlers
   - `find_referencing_symbols()` - Find callers
   - `get_symbols_overview()` - Map module structure
   - `write_memory()` / `read_memory()` - State persistence

**After determining intent and framework, read the appropriate workflow and follow it.**
</routing>

<reference_index>
## References

All in `references/`:

| File | Content |
|------|---------|
| framework-patterns.md | Entry point detection and request flow for Express, Next.js, Fastify, etc. |
| control-flow-types.md | How to present if/switch/try/loops as interactive choices |
| explanation-style.md | Thinking markers, step format, summary format |
| mermaid-templates.md | Mermaid.js flowchart generation from trace path_history |
</reference_index>

<workflows_index>
## Workflows

All in `workflows/`:

| Workflow | Purpose |
|----------|---------|
| trace-request.md | Trace HTTP request from entry to response |
| trace-function.md | Trace a specific function's call chain |
</workflows_index>

<scripts_index>
## Scripts

| Script | Purpose |
|--------|---------|
| detect-framework.sh | Auto-detect project framework from package.json |

Usage:
```bash
./scripts/detect-framework.sh /path/to/project
# Output: express | nextjs-app | nextjs-pages | fastify | hono | nestjs | koa | generic
```
</scripts_index>

<success_criteria>
A successful code trace:
- [ ] Entry point correctly identified and explained
- [ ] Framework detected and appropriate patterns applied
- [ ] At least one branch point presented as interactive choice
- [ ] External dependencies summarized (not deep-traced)
- [ ] User navigated to terminal point OR chose to stop
- [ ] Path history shown in ASCII flowchart format
- [ ] Mermaid flowchart offered as output option (if trace completed)
- [ ] Key insights collected and displayed
- [ ] Trace state available for resume (if user chose to save)
</success_criteria>

<boundaries>
## Boundaries

**Will:**
- Trace application code with full source display
- Explain each step with thinking markers
- Present conditional branches as interactive choices
- Summarize external dependencies at the boundary
- Persist trace state for resume capability

**Will Not:**
- Deep-trace into node_modules or external libraries
- Execute or run the code (read-only analysis)
- Modify any source files
- Make assumptions about runtime values (present all branches)
</boundaries>