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Get Started Free →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.
.claude/skills/oliver-kriska-phx-trace/SKILL.md| Test case | Without → With | Effect | Δ tokens | Δ turns |
|---|---|---|---|---|
| case-01 | ✗→✓ | ▲ Improved | -19% | 0% |
| case-17 | ✗→✓ | ▲ Improved | -5% | 0% |
| case-18 | ✗→✓ | ▲ Improved | -9% | 0% |
| case-22 | ✗→✓ | ▲ Improved | -13% | 0% |
| case-07 | ✓→✗ | ▼ Worse | -41% | 0% |
Build call trees showing how functions are reached from entry points.
mix xref callers first - It's authoritative; grep is fallback only| 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 |
Run the caller query first, then inspect another function in the chain as needed:
bashmix xref callers MyApp.Accounts.update_user/2 mix xref callers MyApp.Accounts.get_user/1
Read the reported locations to see argument patterns.
| 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 |
Trace controller, LiveView, worker, and internal entry-point categories in this session, starting each category with mix xref callers. Native generic workers may handle independent categories in parallel when the runtime provides them, but the same-session sequential path is fully supported and must produce the same call tree. Do not require a named custom agent or Claude-specific spawn configuration.
.claude/plans/{slug}/research/call-tree-{function}.md
For detailed patterns:
references/mix-xref-usage.md - Full mix xref commands and optionsreferences/entry-points.md - All Phoenix/OTP entry point patternsreferences/argument-extraction.md - AST parsing for argument patterns| Case | Status | Duration (ms) | Turns | Tokens | Tool calls | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Without | With | Δ | Without | With | Δ | Without | With | Δ | Without | With | Δ | ||
case-01 | fail→pass | 21,126 | 13,104 | -38% | 1 | 1 | 0% | 3,793 | 3,084 | -19% | 0 | 0 | — |
case-02 | fail→fail | 18,298 | 2,934 | -84% | 1 | 1 | 0% | 3,272 | 935 | -71% | 0 | 0 | — |
case-03 | fail→fail | 15,572 | 2,841 | -82% | 1 | 1 | 0% | 2,859 | 900 | -69% | 0 | 0 | — |
case-04 | pass→pass | 12,145 | 11,069 | -9% | 1 | 1 | 0% | 2,138 | 2,490 | +16% | 0 | 0 | — |
case-05 | pass→pass | 12,723 | 7,591 | -40% | 1 | 1 | 0% | 2,266 | 1,868 | -18% | 0 | 0 | — |
case-06 | pass→pass | 5,910 | 5,358 | -9% | 1 | 1 | 0% | 1,008 | 1,483 | +47% | 0 | 0 | — |
case-07 | pass→fail | 8,869 | 2,031 | -77% | 1 | 1 | 0% | 1,538 | 910 | -41% | 0 | 0 | — |
case-08 | pass→pass | 11,955 | 4,028 | -66% | 1 | 1 | 0% | 1,786 | 1,230 | -31% | 0 | 0 | — |
case-09 | pass→pass | 12,691 | 4,431 | -65% | 1 | 1 | 0% | 2,168 | 1,288 | -41% | 0 | 0 | — |
case-10 | pass→pass | 11,186 | 4,375 | -61% | 1 | 1 | 0% | 1,765 | 1,334 | -24% | 0 | 0 | — |
case-11 | pass→pass | 14,425 | 7,532 | -48% | 1 | 1 | 0% | 2,373 | 1,834 | -23% | 0 | 0 | — |
case-12 | pass→pass | 13,398 | 2,617 | -80% | 1 | 1 | 0% | 1,906 | 950 | -50% | 0 | 0 | — |
case-13 | pass→pass | 12,790 | 4,084 | -68% | 1 | 1 | 0% | 2,022 | 1,221 | -40% | 0 | 0 | — |
case-14 | pass→pass | 11,829 | 4,211 | -64% | 1 | 1 | 0% | 1,921 | 1,211 | -37% | 0 | 0 | — |
case-15 | fail→fail | 18,445 | 3,283 | -82% | 1 | 1 | 0% | 1,912 | 1,185 | -38% | 0 | 0 | — |
case-16 | pass→pass | 16,365 | 7,754 | -53% | 1 | 1 | 0% | 2,592 | 1,721 | -34% | 0 | 0 | — |
case-17 | fail→pass | 14,431 | 9,132 | -37% | 1 | 1 | 0% | 2,149 | 2,031 | -5% | 0 | 0 | — |
case-18 | fail→pass | 12,848 | 6,568 | -49% | 1 | 1 | 0% | 1,877 | 1,701 | -9% | 0 | 0 | — |
case-19 | pass→pass | 14,471 | 5,721 | -60% | 1 | 1 | 0% | 2,407 | 1,545 | -36% | 0 | 0 | — |
case-20 | pass→pass | 14,136 | 6,053 | -57% | 1 | 1 | 0% | 2,194 | 1,527 | -30% | 0 | 0 | — |
case-21 | pass→pass | 12,848 | 3,792 | -70% | 1 | 1 | 0% | 1,980 | 1,149 | -42% | 0 | 0 | — |
case-22 | fail→pass | 9,616 | 4,140 | -57% | 1 | 1 | 0% | 1,403 | 1,214 | -13% | 0 | 0 | — |
DecimalAI ran this skill against gemini-3.6-flash twice over the same eval suite — once with the skill loaded and once without — and compared the two runs case by case. 22 cases were attempted. The headline lift of +14 percentage points is the difference between those two pass rates over the 22 comparable cases. 3 cases got worse with the skill loaded, and they are included in that figure.
Without the skill loaded, the model failed this case. With it loaded, the same prompt on the same model passed. This is one improved case from the latest verified run; every case, including any that regressed, is in the table above.
Other measured skills in the registry, with their headline benchmark lift.