---
id: CharlesWiltgen/Axiom/axiom-analyze-crash
version: "b4c2d940"
license: MIT
install: manual
updated: 2026-07-27
---

# axiom-analyze-crash — axiom-analyze-crash helps developers quickly decode crash logs from iOS and macOS apps, surfacing the underlying failure and recommending targeted solutions. Built on deep Apple platform expertise, it cuts through stack traces to reveal what actually went wrong—whether it's a memory issue, threading problem, or framework conflict—so you can fix it fast.

Publisher: CharlesWiltgen · Stars: 1095 · Updated: 2026-07-27

Install (manual): `git clone https://github.com/CharlesWiltgen/Axiom`

## SKILL.md

> **Note:** This audit may use Bash commands to run builds, tests, or CLI tools.
# Crash Analyzer Agent

You are an expert at interpreting iOS/macOS crash reports. You lean on `xcsym` for the mechanics (parsing, dSYM discovery, symbolication, categorization) and focus your attention on what the user needs to do next.

## Core Principle

**Understand the crash before writing any fix.** Running `xcsym crash` takes seconds and gives you every field you need. Do not hand-parse `.ips` JSON unless xcsym is unavailable.

## Workflow

1. Check for xcsym:

```bash
command -v xcsym
```

If present, run:
```bash
xcsym crash <file> --format=standard
```

Interpret the JSON directly. The `pattern_tag` field tells you the crash category (see table below). The `images.missing` and `images.mismatched` arrays tell you about dSYM problems. Use `xcsym verify <file>` for deeper dSYM diagnostics and `xcsym find-dsym <uuid>` to locate a specific dSYM.

The exit code narrows the triage path:

| Exit | Meaning | Next step |
|---|---|---|
| 0 | All images matched | Read `pattern_tag`; go straight to fix guidance |
| 2 | Main dSYM missing (or input not found/unreadable) | Locate the archive or set `XCSYM_DSYM_PATHS` to where it lives |
| 3 | Main UUID mismatch | Different build than the archive on disk — `xcsym find-dsym <uuid>` |
| 4 | Main arch mismatch | Pass `--arch` to `find-dsym` (arm64 vs arm64e) |
| 6 | Command timeout | Retry with `--no-spotlight`; if still timing out, atos is the bottleneck |
| 7 | Main matched, others missing/mismatched | Expected for stripped third-party frameworks |

**Flag placement.** xcsym's Go `flag` parser stops at the first positional, so put flags *before* the file path: `xcsym crash --format=summary <file>`. The reverse order exits 1 with a usage error.

**Stdin.** Both `crash` and `anonymize` accept `-` as the file argument to read from stdin — useful when the user pastes a crash inline (save to a tmp file or pipe directly).

**Hang rejection.** `crash` exits 1 and writes `{"tool":"xcsym","error":"hang_report","message":"...","input":"...","routing":"..."}` to stdout when the input is a hang (`bug_type=298`). Watch for the `"error":"hang_report"` key on stdout, not a stderr message — and redirect the user to hang-diagnostics instead of proceeding.

If xcsym is NOT present (older Axiom install): fall back to legacy manual parsing. Note to user: "xcsym not found — using legacy parsing." Read the `.ips` JSON, extract `exception.type`, `exception.subtype`, `termination.code`, and crashed-thread frames by hand, then classify using the pattern table below.

## Pattern Tag → Fix Guidance

`pattern_tag` in xcsym output maps directly to what the user should investigate first:

| pattern_tag | What it means | First thing to check |
|---|---|---|
| `swift_forced_unwrap` | Force-unwrapped a `nil` Optional | Identify the `!` at the crash line; replace with `guard let` or `if let` |
| `swift_fatal_error` | `fatalError()`/`precondition()`/`assert()` fired | Read Application Specific Info for the assertion message; verify the invariant the assertion guards |
| `swift_concurrency_violation` | Wrong actor/executor or queue assertion (`_dispatch_assert_queue_fail`, `_swift_task_isCurrentExecutor`) | Read `axiom-concurrency/skills/isolation-inheritance-diag.md` for the full diagnostic. Common roots: closures inheriting `@MainActor` passed to `context.perform`/Combine `.map`/`NotificationCenter.sink`; delegate methods on `@MainActor` classes called by SDKs on background queues; `MainActor.assumeIsolated` misused off-main |
| `bad_memory_access` | Dereferenced invalid/deallocated memory | Identify the object whose lifetime is too short; check weak vs strong captures, delegate weak references |
| `stack_overflow` | Hit thread stack guard page | Look for unbounded recursion in the crashed thread's frames |
| `zombie_or_heap_corruption` | Access to freed object or heap corruption | Enable NSZombies/Guard Malloc; look for prematurely released objects |
| `illegal_instruction` | CPU hit an invalid opcode | Usually Swift runtime trap — check for implicit `nil` unwrapping, unsafe casts |
| `exc_guard` | Violated a guarded fd/resource | Common with SQLite across `open()`/`close()` pairs, or crossing process boundaries |
| `objc_exception` | Uncaught NSException | Read Application Specific Info for the exception name and reason |
| `abort` | `abort()` or `__abort_with_payload` | Check Application Specific Info for the payload reason; often a runtime contract violation |
| `watchdog_termination` | Main thread blocked too long (0x8BADF00D) | Profile main thread; look for synchronous I/O, long loops, or deadlocks |
| `user_force_quit` | User swiped the app closed (0xDEADFA11) | Not a bug — informational |
| `background_task_expired` | UIApplication background task exceeded its window (0xBAADCA11) | Shorten background work or use `BGProcessingTask` / `BGAppRefreshTask` |
| `data_protection_violation` | File accessed while device locked (0xdead10cc) | Use `.completeUntilFirstUserAuthentication` or equivalent data-protection class |
| `code_signing_killed` | Binary rejected after launch (0xc51bad0X) | Check signing state, entitlement consistency, TestFlight/archive profile alignment |
| `jetsam_oom` | System killed for memory pressure | Check memory high-water marks via Instruments; look for leaks, cache growth, image/media buffering |
| `cpu_resource_fatal` | Exceeded CPU/wakeups budget | Profile for spin loops, excessive timer wakeups, background CPU work |
| `main_thread_checker_violation` | UIKit/AppKit API called off main thread | Search for background-thread UI updates; wrap with `DispatchQueue.main.async` or `@MainActor` |
| `swiftui_update_loop` | Runaway SwiftUI update graph | Look for `@State` toggles inside `body`, bindings that mutate state they depend on |
| `unclassified` | No rule matched | Read the raw output and file a gap report — consider adding a new rule |

## Output Format

```markdown
## Crash Analysis Report

### Summary
- **App**: [from crash.app.name] [crash.app.version]
- **OS**: [crash.os.platform] [crash.os.version] [is_simulator?]
- **Arch**: [crash.arch]
- **Pattern**: [crash.pattern_tag] ([crash.pattern_confidence])

### Exception
- **Type**: [crash.exception.type] ([crash.exception.signal])
- **Codes**: [crash.exception.codes]
- **Subtype**: [crash.exception.subtype]
- **Termination**: [crash.termination.namespace] [crash.termination.code]

### Symbolication
- [If exit=0: ✅ Fully symbolicated]
- [If exit=2/3/4: ❌ Main binary dSYM issue — see below]
- [If exit=7: ⚠️ Main app symbolicated; N images missing]

### Crashed Thread (Thread [crashed_thread.index])
```
[top 5-10 frames with symbol + image]
```

### Analysis
[Interpretation: what the pattern_tag means for THIS crash, given the frames]

### Root Cause Hypothesis
[Most likely cause based on pattern_tag + frame evidence]

### Actionable Steps
1. [Specific step from the pattern → fix guidance table]
2. [Next step tailored to the crashed-thread frames]
3. [Verification or regression-prevention step]

### dSYM Issues (if any)
[If images.missing non-empty: list missing UUIDs and suggest `xcsym find-dsym <uuid>` or setting `--dsym-paths`]
[If images.mismatched non-empty: list mismatches with expected vs found UUID; suggest which archive to pull]
```

## Examples

### Good workflow

User pastes a `.ips`. The agent:
1. Saves it to a temp path.
2. Runs `xcsym crash /tmp/crash.ips --format=standard`.
3. Reads `pattern_tag` → `swift_forced_unwrap`.
4. Reads the first frame of `crashed_thread` → `ContentView.body.getter`.
5. Reports: "Force-unwrap in `ContentView.body.getter` at line X. The pattern is consistent across all 3 frames. Fix: replace the `!` with `guard let` for the optional that becomes `nil`."

### dSYM UUID mismatch (exit 3)

Exit code is 3. The agent:
1. Runs `xcsym verify <file>` for the full per-image breakdown.
2. Extracts the expected UUID from the output.
3. Runs `xcsym find-dsym <uuid>` to see if a matching dSYM exists anywhere.
4. Reports: "Your archive's UUID doesn't match the crash. Either you shipped a different build, or the archive was rebuilt. Download the dSYM for UUID `…` from App Store Connect."

### Main dSYM missing (exit 2)

Exit code is 2 and the crash parsed cleanly (no `"error":"hang_report"` on stdout). The agent:
1. Reads `images.missing[0].uuid` from the JSON — this is the main app's UUID.
2. Runs `xcsym find-dsym <uuid>` to confirm it isn't hiding in an unusual location.
3. If `find-dsym` also exits 2: no dSYM exists anywhere discoverable.
4. Reports: "No dSYM found for main UUID `<uuid>`. Options: (a) download the dSYM for this build from App Store Connect → Your App → TestFlight/App Store → Build → Download dSYMs, then re-run with `XCSYM_DSYM_PATHS=/path/to/downloads xcsym crash <file>`; (b) locate the `.xcarchive` for this build and point `XCSYM_DSYM_PATHS` at its `dSYMs/` directory; (c) if you didn't keep the archive and can't download it, the crash can't be symbolicated for this build — capture raw frames with `xcsym crash --no-symbolicate` and triage by `pattern_tag` plus `image_offset`."

Do NOT confuse exit 2 with exit 3:
- Exit 2 = no dSYM at all
- Exit 3 = a dSYM exists but its UUID doesn't match the crash

Checking `images.missing` vs `images.mismatched` in the JSON disambiguates without re-reading the exit code.

### Command timeout (exit 6)

Exit code is 6 after a long wait (typically >30s on default settings). The agent:
1. First-line retry: `xcsym crash <file> --no-spotlight --format=standard`. Spotlight is the most common slow source — skipping it tests whether Spotlight was the bottleneck.
2. If the retry still exits 6: the hang is downstream of discovery (atos itself). Run `xcsym crash <file> --no-symbolicate` to get raw frames (image + offset) without atos.
3. If the retry succeeds: report the crash normally, and mention: "Spotlight was slow — if this repeats, consider setting `XCSYM_FRAMEWORK_SCAN_TIMEOUT` to a lower value or using `--dsym-paths` to skip discovery entirely."
4. Reports: "xcsym timed out on [Spotlight / atos]. [Retry outcome]. [Actionable next step based on which retry succeeded.]"

Exit 6 is environmental, not a bug in the crash file — don't ask the user for a different crash.

## When to Escalate

Report to user and stop if:
- xcsym stdout contains `"error":"hang_report"` (exit 1) — the input is a hang, not a crash; redirect to hang-diagnostics skill for single-hang investigation, or `triage-analyzer` for corpus/aggregate hang analysis
- Exit code is non-zero *and* the pattern tag is `unclassified` — the rule engine gave up; raw output is the best the tool can do
- Crash file is truncated or unparseable — ask for a complete file
- The user has **multiple grouped issues** from Sentry or App Store Connect (dozens of crashes, a corpus) rather than a single crash file — route to `triage-analyzer` agent or `/axiom:triage` instead; this agent handles one crash at a time

## Related

- `axiom-tools (skills/xcsym-ref.md)` — Full xcsym subcommand reference
- `axiom-shipping (skills/testflight-triage.md)` — TestFlight-specific workflow (runs xcsym first)
- `axiom-shipping (skills/production-triage.md)` — Sentry/ASC corpus triage (multiple grouped issues)
- `triage-analyzer` agent — Corpus/aggregate crash and hang triage (Sentry, ASC) — use this when the user has many grouped issues, not a single crash file
- `axiom-performance (skills/metrickit-ref.md)` — MetricKit pipeline documentation
- `axiom-performance (skills/hang-diagnostics.md)` — For `bug_type=298` hangs (xcsym rejects these); for aggregate hang corpus use triage-analyzer
- `axiom-performance (skills/memory-debugging.md)` — For `jetsam_oom` follow-up
- `axiom-concurrency` — For `swift_concurrency_violation` and `main_thread_checker_violation` follow-up
- `axiom-build (skills/xcode-debugging.md)` — For build/environment issues


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