Axiom axiom-analyze-crash

Use when the user has a crash log (.

install

source · Clone the upstream repo

git clone https://github.com/CharlesWiltgen/Axiom

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/CharlesWiltgen/Axiom "$T" && mkdir -p ~/.claude/skills && cp -r "$T/axiom-codex/skills/axiom-analyze-crash" ~/.claude/skills/charleswiltgen-axiom-axiom-analyze-crash && rm -rf "$T"

manifest: axiom-codex/skills/axiom-analyze-crash/SKILL.md

source content

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

Check for xcsym:

command -v xcsym

If present, run:

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

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	Check `@MainActor` annotations, `assumeIsolated` boundaries, dispatch queue assertions
`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

## 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:

Saves it to a temp path.

Runs

xcsym crash /tmp/crash.ips --format=standard

Reads
```
pattern_tag
```
→
```
swift_forced_unwrap
```
.
Reads the first frame of
```
crashed_thread
```
→
```
ContentView.body.getter
```
.
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:

Runs
```
xcsym verify <file>
```
for the full per-image breakdown.
Extracts the expected UUID from the output.
Runs
```
xcsym find-dsym <uuid>
```
to see if a matching dSYM exists anywhere.
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:

Reads
```
images.missing[0].uuid
```
from the JSON — this is the main app's UUID.
Runs
```
xcsym find-dsym <uuid>
```
to confirm it isn't hiding in an unusual location.
If
```
find-dsym
```
also exits 2: no dSYM exists anywhere discoverable.
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

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:

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.
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.
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."
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
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

```
axiom-tools (skills/xcsym-ref.md)
```
— Full xcsym subcommand reference
```
axiom-shipping (skills/testflight-triage.md)
```
— TestFlight-specific workflow (runs xcsym first)

axiom-performance (skills/metrickit-ref.md)

— MetricKit pipeline documentation

axiom-performance (skills/hang-diagnostics.md)

— For

bug_type=298

hangs (xcsym rejects these)

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

Axiom axiom-analyze-crash

Crash Analyzer Agent

Core Principle

Workflow

Pattern Tag → Fix Guidance

Output Format

Examples

Good workflow

dSYM UUID mismatch (exit 3)

Main dSYM missing (exit 2)

Command timeout (exit 6)

When to Escalate

Related