Portable Tools - Cross-Device Development Methodology

Methodology for building tools that work across different devices, naming schemes, and configurations. Based on lessons from OAuth refresher debugging session (2026-01-23).

Core Principle

Never assume your device is the only device.

Your local setup is just one of many possible configurations. Build for the general case, not the specific instance.

The Three Questions (Before Writing Code)

1. "What varies between devices?"

Before writing any code that reads configuration, data, or credentials:

Ask: - File paths? (macOS vs Linux, different home dirs) - Account names? (user123 vs default vs oauth) - Service names? (slight variations in spelling/capitalization) - Data structure? (different versions, different formats) - Environment? (different shells, different tools available)

Example from OAuth refresher: - ❌ Assumed: Account is always "claude" - ✅ Reality: Could be "claude", "Claude Code", "default", etc.

Action: List variables, make them configurable or auto-discoverable

2. "How do I prove this works?"

Before claiming success:

Require: - Concrete BEFORE state (exact values) - Concrete AFTER state (exact values) - Proof they're different (side-by-side comparison)

Example from OAuth refresher: ``` BEFORE: - Access Token: POp5z1fi...eSN9VAAA - Expires: 1769189639000

AFTER: - Access Token: 01v0RrFG...eOE9QAA ✅ Different - Expires: 1769190268000 ✅ Extended ```

Action: Always show data transformation with real values

3. "What happens when it breaks?"

Before pushing to production:

Test: - Wrong configuration (intentionally break config) - Missing data (remove expected fields) - Multiple entries (ambiguous case) - Edge cases (empty values, special characters)

Example from OAuth refresher: - Test with keychain_account: "wrong-name" → Fallback should work - Test with incomplete keychain data → Should fail gracefully with helpful error

Action: Test failure modes, not just happy path

Mandatory Patterns

Pattern 1: Explicit Over Implicit

❌ Wrong: ```bash

Ambiguous - returns first match

security find-generic-password -s "Service" -w ```

✅ Correct: ```bash

Explicit - returns specific entry

security find-generic-password -s "Service" -a "account" -w ```

Rule: If a command can be ambiguous, make it explicit.

Pattern 2: Validate Before Use

❌ Wrong: bash DATA=$(read_config) USE_VALUE="$DATA" # Hope it's valid

✅ Correct: bash DATA=$(read_config) if ! validate_structure "$DATA"; then error "Invalid data structure" fi USE_VALUE="$DATA"

Rule: Never assume data has expected structure.

Pattern 3: Fallback Chains

❌ Wrong: bash ACCOUNT="claude" # Hardcoded

✅ Correct: ```bash

Try configured → Try common → Error with help

ACCOUNT="${CONFIG_ACCOUNT}" if ! has_data "$ACCOUNT"; then for fallback in "claude" "default" "oauth"; do if has_data "$fallback"; then ACCOUNT="$fallback" break fi done fi [[ -z "$ACCOUNT" ]] && error "No account found. Tried: ..." ```

Rule: Provide automatic fallbacks for common variations.

Pattern 4: Helpful Errors

❌ Wrong: bash [[ -z "$TOKEN" ]] && error "No token"

✅ Correct: ```bash [[ -z "$TOKEN" ]] && error "No token found

Checked: - Config: $CONFIG_FILE - Field: $FIELD_NAME - Expected: { \"tokens\": { \"refresh\": \"...\" } }

Verify with: cat $CONFIG_FILE | jq '.tokens' " ```

Rule: Error messages should help user diagnose and fix.

Debugging Methodology (Patrick's Approach)

Step 1: Get Exact Data

Don't ask: "Is it broken?"
Ask: "What exact values do you see? How many entries exist? Which one has the data?"

Example: ```bash

Vague

"Check keychain"

Specific

"Run: security find-generic-password -l 'Service' | grep 'acct'" "Tell me: 1. How many entries 2. Which has tokens 3. Last modified" ```

Step 2: Prove With Concrete Examples

Don't say: "It should work now"
Show: "Here's the BEFORE token (POp5z...), here's AFTER (01v0R...), they're different"

Template: ``` BEFORE: - Field1: - Field2:

AFTER: - Field1: ✅ Changed - Field2: ✅ Changed

PROOF: Values are different ```

Step 3: Think Cross-Device Immediately

Don't think: "Works on my machine"
Think: "What if their setup differs in [X]?"

Checklist: - [ ] Different account names? - [ ] Different file paths? - [ ] Different tools/versions? - [ ] Different permissions? - [ ] Different data formats?

Pre-Flight Checklist (Before Publishing)

Discovery Phase

[ ] List all external dependencies (files, commands, services)
[ ] Document what each dependency provides
[ ] Identify which parts could vary between devices

Implementation Phase

[ ] Make variations configurable (with sensible defaults)
[ ] Add validation for each input
[ ] Build fallback chains for common variations
[ ] Add --dry-run or --test mode

Testing Phase

[ ] Test with correct config → Should work
[ ] Test with wrong config → Should fallback or fail gracefully
[ ] Test with missing data → Should give helpful error
[ ] Test with multiple entries → Should handle ambiguity

Documentation Phase

[ ] Document default assumptions
[ ] Document how to verify local setup
[ ] Document common variations and how to handle them
[ ] Include data flow diagram
[ ] Add troubleshooting section

Real-World Example: OAuth Refresher

Original (Broken)

# Assumes single entry, no validation, no fallback
KEYCHAIN_DATA=$(security find-generic-password -s "Service" -w)
REFRESH_TOKEN=$(echo "$KEYCHAIN_DATA" | jq -r '.refreshToken')
# Use token (hope it's valid)

Problems: - Returns first alphabetical match (wrong entry) - No validation (could be empty/malformed) - No fallback (fails if account name differs)

Fixed (Portable)

# Explicit account with validation and fallback
validate_data() {
    echo "$1" | jq -e '.claudeAiOauth.refreshToken' > /dev/null 2>&1
}

# Try configured account
DATA=$(security find-generic-password -s "$SERVICE" -a "$ACCOUNT" -w 2>&1)
if validate_data "$DATA"; then
    log "✓ Using account: $ACCOUNT"
else
    log "⚠ Trying fallback accounts..."
    for fallback in "claude" "Claude Code" "default"; do
        DATA=$(security find-generic-password -s "$SERVICE" -a "$fallback" -w 2>&1)
        if validate_data "$DATA"; then
            ACCOUNT="$fallback"
            log "✓ Found data in: $fallback"
            break
        fi
    done
fi

[[ -z "$DATA" ]] || ! validate_data "$DATA" && error "No valid data found
Tried accounts: $ACCOUNT, claude, Claude Code, default
Verify with: security find-generic-password -l '$SERVICE'"

REFRESH_TOKEN=$(echo "$DATA" | jq -r '.claudeAiOauth.refreshToken')

Improvements: - ✅ Explicit account parameter - ✅ Validates data structure - ✅ Automatic fallback to common names - ✅ Helpful error with verification command

Common Anti-Patterns

Anti-Pattern 1: "Works On My Machine"

FILE="/Users/patrick/.config/app.json"  # Hardcoded path

Fix: Use $HOME, detect OS, or make configurable

Anti-Pattern 2: "Hope It's There"

TOKEN=$(cat config.json | jq -r '.token')
# What if .token doesn't exist? Script continues with empty value

Fix: Validate before using bash TOKEN=$(cat config.json | jq -r '.token // empty') [[ -z "$TOKEN" ]] && error "No token in config"

Anti-Pattern 3: "First Match Is Right"

# If multiple entries exist, which one?
ENTRY=$(find_entry "service")

Fix: Be explicit or enumerate all ```bash ENTRY=$(find_entry "service" "account") # Specific

OR

ALL=$(find_all_entries "service") for entry in $ALL; do validate_and_use "$entry" done ```

Anti-Pattern 4: "Silent Failures"

process_data || true  # Ignore errors

Fix: Fail loudly with context bash process_data || error "Failed to process Data: $DATA Expected: { ... } Check: command_to_verify"

Integration With Existing Workflows

With sprint-plan.md

Add to testing section: ```markdown

Cross-Device Testing

[ ] Test with different account names
[ ] Test with wrong config values
[ ] Test with missing data
[ ] Document fallback behavior ```

With PRIVACY-CHECKLIST.md

Add before publishing: ```markdown

Portability Check

[ ] No hardcoded paths (use $HOME, detect OS)
[ ] No hardcoded names (use config or fallback)
[ ] Validation on all inputs
[ ] Helpful errors for common issues ```

With skill-creator

When building new skills: 1. List what varies between devices 2. Make it configurable or auto-discoverable 3. Test with wrong config 4. Document troubleshooting

Quick Reference Card

Before writing code: 1. What varies between devices? 2. How do I prove this works? 3. What happens when it breaks?

Mandatory patterns: - Explicit over implicit - Validate before use - Fallback chains - Helpful errors

Testing: - Correct config → Works - Wrong config → Fallback or helpful error - Missing data → Clear diagnostic

Documentation: - Data flow diagram - Common variations - Troubleshooting guide

Success Criteria

A tool is portable when:

✅ Works on different devices without modification
✅ Auto-discovers common variations in setup
✅ Fails gracefully with actionable error messages
✅ Can be debugged by reading the error output
✅ Documentation covers "what if my setup differs"

Test: Give it to someone with a different setup. If they need to ask you questions, the tool isn't portable yet.

Origin Story

This methodology emerged from debugging the OAuth refresher (2026-01-23): - Script read wrong keychain entry (didn't specify account) - Assumed single entry existed (multiple did) - No validation (used empty data) - No fallback (failed on different account names)

Patrick's approach: 1. Asked for exact data (how many entries, which has tokens) 2. Demanded proof (show BEFORE/AFTER tokens) 3. Thought cross-device (what if naming differs?)

Result: Tool went from single-device/broken to universal/production-ready.

Key insight: The bugs weren't in the logic - they were in the assumptions.

When To Use This Skill

Use when: - Building tools that read system configuration - Working with keychains, credentials, environment variables - Creating scripts that run on multiple machines - Publishing skills to ClawdHub (others will use them)

Apply: 1. Before implementing: Answer the three questions 2. During implementation: Use mandatory patterns 3. Before testing: Run pre-flight checklist 4. After testing: Document variations and troubleshooting

Remember: Your device is just one case. Build for the general case.

Portable Tools