How do I install the Phx Trace skill?

Run npx skillmds@latest add majiayu000/phx-trace-3 in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Phx Trace safe to use?

This skill has not completed SkillMD's automated safety review yet. Independent scanners report: SkillSpector: PASS, Skill Scanner: PASS. Capability flags: makes network calls. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Phx Trace?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Phx Trace free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Phx Trace?

majiayu000 (@majiayu000) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Phx Trace by majiayu000 — Agent Skill

Name: Phx Trace
Rating: 4.5 (4 reviews)
Author: majiayu000

File contents

Call Tracing

Build call trees showing how functions are reached from entry points.

Iron Laws - Never Violate These

Always use mix xref callers first - It's authoritative; grep is fallback only
Stop at entry points - Controllers, LiveView callbacks, Oban workers, GenServer callbacks
Track visited MFAs - Prevent infinite loops from circular calls
Extract argument patterns - Just knowing "who calls" isn't enough; HOW they call matters
Max depth 10 - Deeper trees indicate architectural issues, not useful traces

When to Build Call Tree (Use Proactively)

Condition	Why Call Tree Helps
Unexpected nil/value at runtime	Trace where the value originates
Bug can't reproduce locally	See all entry points that reach the code
Changing function signature	Find all callers and their argument patterns
Incomplete stack trace	Get full path context
"Where does X come from?"	Visual answer to data flow question

Quick Trace

Run mix xref callers MyApp.Accounts.update_user/2 to find all callers. Then read the reported locations to see argument patterns.

Entry Points (Stop Here)

Pattern	Type
`def mount/3`, `def handle_event/3`	LiveView
`def index/2`, `def show/2`, `def create/2`	Controller
`def perform(%Oban.Job{})`	Oban Worker
`def handle_call/3`, `def handle_cast/2`	GenServer

Delegate to call-tracer Agent

For full recursive tree with argument extraction and parallel category tracing:

Agent(subagent_type: "call-tracer", prompt: "Build call tree for MyApp.Accounts.update_user/2")

The call-tracer agent uses parallel subagents for each entry point category:

Controllers subagent (HTTP paths)
LiveView subagent (WebSocket paths)
Workers subagent (Background jobs)
Internal subagent (Cross-context calls)

Each gets fresh 200k context for deep exploration.

Output Location

.claude/plans/{slug}/research/call-tree-{function}.md

References

For detailed patterns:

references/mix-xref-usage.md - Full mix xref commands and options
references/entry-points.md - All Phoenix/OTP entry point patterns
references/argument-extraction.md - AST parsing for argument patterns

---name: phx-trace-3description: Trace Elixir call trees from entry points via mix xref. Use when debugging data flow, planning signature changes, or understanding how a bug reaches code.---# Call TracingBuild call trees showing how functions are reached from entry points.## Iron Laws - Never Violate These1. **Always use `mix xref callers` first** - It's authoritative; grep is fallback only2. **Stop at entry points** - Controllers, LiveView callbacks, Oban workers, GenServer callbacks3. **Track visited MFAs** - Prevent infinite loops from circular calls4. **Extract argument patterns** - Just knowing "who calls" isn't enough; HOW they call matters5. **Max depth 10** - Deeper trees indicate architectural issues, not useful traces## When to Build Call Tree (Use Proactively)| Condition | Why Call Tree Helps ||-----------|---------------------|| Unexpected nil/value at runtime | Trace where the value originates || Bug can't reproduce locally | See all entry points that reach the code || Changing function signature | Find all callers and their argument patterns || Incomplete stack trace | Get full path context || "Where does X come from?" | Visual answer to data flow question |## Quick TraceRun `mix xref callers MyApp.Accounts.update_user/2` to find all callers. Then read the reported locations to see argument patterns.## Entry Points (Stop Here)| Pattern | Type ||---------|------|| `def mount/3`, `def handle_event/3` | LiveView || `def index/2`, `def show/2`, `def create/2` | Controller || `def perform(%Oban.Job{})` | Oban Worker || `def handle_call/3`, `def handle_cast/2` | GenServer |## Delegate to call-tracer AgentFor full recursive tree with argument extraction and **parallel category tracing**:```Agent(subagent_type: "call-tracer", prompt: "Build call tree for MyApp.Accounts.update_user/2")```The call-tracer agent uses **parallel subagents** for each entry point category:- Controllers subagent (HTTP paths)- LiveView subagent (WebSocket paths)- Workers subagent (Background jobs)- Internal subagent (Cross-context calls)Each gets fresh 200k context for deep exploration.## Output Location`.claude/plans/{slug}/research/call-tree-{function}.md`## ReferencesFor detailed patterns:- `references/mix-xref-usage.md` - Full mix xref commands and options- `references/entry-points.md` - All Phoenix/OTP entry point patterns- `references/argument-extraction.md` - AST parsing for argument patterns

Frequently asked questions

Phx Trace