formatting-build-output

xcsift - Xcode Build Output Formatter

xcsift parses and formats xcodebuild/SPM output into token-efficient TOON format optimized for LLM consumption. It extracts compile errors, warnings, test failures, code coverage, and build timing from verbose Xcode output.

When to Use

Always pipe through xcsift when running:

• xcodebuild build / xcodebuild test
• swift build / swift test
• Any command that produces Xcode/SPM build output

Usage Pattern

Always redirect stderr and use TOON format:

# Build
xcodebuild build 2>&1 | xcsift -f toon
swift build 2>&1 | xcsift -f toon

# Test
swift test 2>&1 | xcsift -f toon
xcodebuild test 2>&1 | xcsift -f toon

# With warnings
xcodebuild build 2>&1 | xcsift -f toon -w

# With code coverage
swift test --enable-code-coverage 2>&1 | xcsift -f toon -c
xcodebuild test -enableCodeCoverage YES 2>&1 | xcsift -f toon -c

# With detailed per-file coverage
swift test --enable-code-coverage 2>&1 | xcsift -f toon -c --coverage-details

# With executable targets
xcodebuild build 2>&1 | xcsift -f toon -e

# Strict CI mode (fail on warnings or errors)
xcodebuild build 2>&1 | xcsift -f toon -W -E

# Slow test detection
swift test 2>&1 | xcsift -f toon --slow-threshold 1.0

# Build info (per-target phases, timing, dependencies)
xcodebuild build 2>&1 | xcsift -f toon --build-info

Key Flags

Flag	Description
-f toon	TOON format (30-60% fewer tokens than JSON)
-w	Show detailed warnings list
-W	Treat warnings as errors (Werror)
-q	Quiet mode (no output on clean success)
-c	Include code coverage summary
--coverage-details	Per-file coverage breakdown (use with -c)
-e	Include executable targets
-E	Exit with non-zero code on build failure
--build-info	Per-target phases, timing, and dependencies
--slow-threshold N	Flag tests slower than N seconds
--config PATH	Use custom config file (default: .xcsift.toml)
--init	Generate .xcsift.toml template in current directory

Interpreting TOON Output

TOON uses indentation-based structure with tabular arrays:

status: failed
summary:
  errors: 1
  warnings: 3
  failed_tests: 2
  passed_tests: 10
  build_time: 12.4s
  test_time: 5.2s
errors[1]{file,line,message}:
  main.swift,15,"use of undeclared identifier 'foo'"
warnings[3]{file,line,message,type}:
  Parser.swift,20,"unused variable 'result'",compile
  View.swift,42,"Publishing changes from background threads",swiftui
  Util.swift,10,"Custom warning message",runtime
failed_tests[2]{suite,test,file,line,message,duration}:
  MyTests,testExample,MyTests.swift,25,"XCTAssertEqual failed",0.123
  MyTests,testOther,MyTests.swift,30,"XCTAssertTrue failed",0.456

Key patterns:

• status: succeeded or failed
• errors[N]{columns}: — tabular array with N items, column names in braces
• warnings have type: compile, runtime, or swiftui
• failed_tests include file/line for navigation and duration
• null values mean the data wasn't available (e.g., build_time: null if not parsed)

Troubleshooting

Problem	Solution
No errors shown but build failed	Add 2>&1 to capture stderr
Coverage shows null	Add --enable-code-coverage (SPM) or -enableCodeCoverage YES (xcodebuild)
"xcsift not found"	Install: brew install xcsift or swift build -c release && cp .build/release/xcsift /usr/local/bin/
Coverage for wrong target	xcsift auto-filters to tested target; use --coverage-path to override
Config not loading	Check .xcsift.toml in CWD or ~/.config/xcsift/config.toml

Important

• Always use 2>&1 to capture stderr (compiler errors and warnings go to stderr)
• TOON format reduces tokens by 30-60% compared to raw xcodebuild output
• The pre-tool hook automatically wraps build commands when the plugin is installed
• Flaky test detection is automatic (no flag needed) — detects tests that both pass and fail