ax-build

ax-build is a skill for Claude Code from Kasempiternal/axiom-v2. It costs 26 tokens per session (4,187 once invoked), scanned C, original, MIT.

A troubleshooting guide for Xcode builds, dependencies, tests, simulators, performance, and TestFlight crashes. Xcode is Apple’s tool for building and testing apps.

In plain words
What is it for?
Use it to investigate failed builds, missing packages, crashing tests, simulator problems, slow builds, stale Derived Data, and crashes reported from TestFlight.
Why use it?
It helps distinguish problems in the code from stale build files, stuck simulators, dependency caches, or other environment issues. It provides diagnostic and cleanup patterns for common failures.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: positional $N argument.

Part of the axiom plugin — 40 skills, 8 commands, 12 agents, 2 hooks shipped together

Good fit Use it to investigate failed builds, missing packages, crashing tests, simulator problems, slow builds, stale Derived Data, and crashes reported from TestFlight.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/kasempiternal/axiom-v2/ax-build
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add Kasempiternal/axiom-v2 --skill ax-build
Clone the repo
git clone --depth 1 https://github.com/Kasempiternal/axiom-v2

Made for: Claude Code.

Or install axiom, the plugin that ships this one along with the rest of its 40 skills, 8 commands, 12 agents, 2 hooks.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for ax-build

README.md
[![agentmods](https://agentmods.dev/badge/skills/kasempiternal/axiom-v2/ax-build/github.svg)](https://agentmods.dev/skills/kasempiternal/axiom-v2/ax-build)
Your own site
<a href="https://agentmods.dev/skills/kasempiternal/axiom-v2/ax-build"><img src="https://agentmods.dev/badge/skills/kasempiternal/axiom-v2/ax-build/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for ax-build

Your own site · 80×15
<a href="https://agentmods.dev/skills/kasempiternal/axiom-v2/ax-build"><img src="https://agentmods.dev/badge/skills/kasempiternal/axiom-v2/ax-build.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,187 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00026 $0.04187
Opus 5 $0.00013 $0.02093
Sonnet 5 $0.00005 $0.00837
Haiku 4.5 $0.00003 $0.00419

Measured 10d ago against content hash 42cb6fd4449b, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade C, and why

ax-build scanned grade C with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 10d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Recursive force deletehighDestructive command

rm -rf with a variable or a broad path is one typo away from removing the wrong tree.

rm -rf ~/Library/Developer/Xcode/DerivedData/*
axiom-plugin/skills/ax-build/SKILL.md · 530 lines

How it starts

The opening of the file, as written. The whole thing — 530 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Build & Fix

Quick Patterns

Environment-First Diagnostics (Run BEFORE Debugging Code)

80% of mysterious Xcode issues are environment problems, not code bugs.

# 1. Check for zombie processes
ps aux | grep -E "xcodebuild|Simulator" | grep -v grep

# 2. Check Derived Data size (>10GB = stale)
du -sh ~/Library/Developer/Xcode/DerivedData

# 3. Check simulator states
xcrun simctl list devices | grep -E "Booted|Booting|Shutting Down"

Interpretation:

  • 0 processes + small Derived Data + no stuck sims = environment clean, investigate code
  • 10+ processes OR >10GB OR stuck simulators = environment problem, clean first
  • Stale code executing OR intermittent failures = clean Derived Data regardless of size

Clean Everything (Stale Builds / "No such module")

xcodebuild clean -scheme YourScheme
rm -rf ~/Library/Developer/Xcode/DerivedData/*
rm -rf .build/ build/
xcodebuild build -scheme YourScheme \
  -destination 'platform=iOS Simulator,name=iPhone 16'

SPM Package Not Found

rm -rf ~/Library/Developer/Xcode/DerivedData
rm -rf ~/Library/Caches/org.swift.swiftpm
xcodebuild -resolvePackageDependencies
xcodebuild clean build -scheme YourScheme

CocoaPods Clean Reinstall

rm -rf Pods/
rm Podfile.lock
pod install
open YourApp.xcworkspace   # Always workspace, never .xcodeproj

Simulator Recovery

xcrun simctl shutdown all
xcrun simctl list devices
# If still stuck:
xcrun simctl erase <device-uuid>
# Nuclear option:
killall -9 Simulator

Kill Zombie Processes

killall -9 xcodebuild
ps aux | grep xcodebuild | grep -v grep

Isolate Failing Test

xcodebuild test -scheme YourScheme \
  -destination 'platform=iOS Simulator,name=iPhone 16' \
  -only-testing:YourTests/SpecificTestClass

Crash Log Analysis

# Recent crashes
ls -lt ~/Library/Logs/DiagnosticReports/*.crash | head -5

# Symbolicate address
atos -o YourApp.app.dSYM/Contents/Resources/DWARF/YourApp \
  -arch arm64 0x<address>

Read the full file on GitHub · 530 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 10d ago First seen · 530 lines · 26 tokens per session scan C 42cb6fd4449b

Subscribe to this mod's changes

ax-build is a skill published in the GitHub repository Kasempiternal/axiom-v2 (4 stars, last pushed 6mo ago), licensed MIT. It adds 26 tokens to every session and 4,187 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it C with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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