code-trace

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Interactive code execution path tracer that explains how code flows from entry point to output. Uses step-by-step navigation with AskUserQuestion to explore conditional branches and function calls. Use when: - User asks "How does X work in this codebase?" - User wants to understand HTTP request/response flow - User asks about middleware execution order - User wants to trace a function call chain - User asks "What happens when..." questions - User wants to learn how code paths connect Keywords: trace, flow, execution, path, call chain, middleware, request handling, what happens, how does, step through, follow the code

7installs
Sourcelaststance/skills
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NPX Install

npx skill4agent add laststance/skills code-trace

Tags

Translated version includes tags in frontmatter
code-tracingexecution-path-analysisrequest-flow-tracingfunction-call-chainstate-persistence

SKILL.md Content

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<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 PatternPresentation
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/
:
FileContent
framework-patterns.mdEntry point detection and request flow for Express, Next.js, Fastify, etc.
control-flow-types.mdHow to present if/switch/try/loops as interactive choices
explanation-style.mdThinking markers, step format, summary format
</reference_index>
<workflows_index>

Workflows

All in 
workflows/
:
WorkflowPurpose
trace-request.mdTrace HTTP request from entry to response
trace-function.mdTrace a specific function's call chain
</workflows_index>
<scripts_index>

Scripts

ScriptPurpose
detect-framework.shAuto-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
  • 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>