Portable Tools

Build cross-device tools without hardcoding paths or account names

Security Scan

The skill is a documentation/methodology pack for building portable shell tools and is internally consistent, but its runtime guidance encourages revealing raw tokens/secret values for “proof,” which is a privacy risk users should mitigate.

Purpose & Capability

Name and description match the actual contents: a methodology, examples, and a pre-publish checklist for making shell tools portable. There are no unexpected binaries, environment variables, or unrelated install steps required.

Instruction Scope

SKILL.md and examples explicitly instruct running platform commands (e.g., macOS 'security find-generic-password') and showing BEFORE/AFTER token values. That is coherent for debugging auth portability, but the explicit encouragement to paste raw tokens and access keychain output increases the chance of accidental secrets disclosure. The instructions do not instruct reading unrelated system files or sending data to external endpoints, but they do ask for concrete secret values as 'proof.'

Install Mechanism

Instruction-only skill with no install spec and no downloads. No files are written or arbitrary code fetched during install—lowest-risk install posture.

Credentials

The skill does not declare any required environment variables or credentials (none listed). However, examples/diagnostics reference local credential stores (keychain) and tokens. This is reasonable for an OAuth/tool-portability guide, but users should be aware that following the examples may surface local credentials. The declared requirements are proportionate to the stated purpose.

Persistence & Privilege

The skill is not always-included, does not request persistent system privileges, and contains no install hooks. It does not modify other skills or system-wide settings.

Assessment

This skill is a portable-tooling guide and is internally consistent, but some examples explicitly ask you to show raw tokens and keychain output as "proof." Before using: (1) do NOT paste raw access tokens or secrets into public chat or logs — redact or hash them (e.g., show first/last 4 chars or a SHA256 of the token) when proving changes; (2) run the pre-publish checklist and debugging commands locally in a safe environment, not in a public/shared session; (3) if an agent or helper asks for BEFORE/AFTER values, prefer deterministic comparisons (hashes) or masked output instead of full secrets; (4) consider adding guidance to SKILL.md that any exported or reported token values must be redacted and that proofs should use non-reversible fingerprints rather than raw tokens.

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:

# Ambiguous - returns first match
security find-generic-password -s "Service" -w

✅ Correct:

# 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:

DATA=$(read_config)
USE_VALUE="$DATA"  # Hope it's valid

✅ Correct:

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:

ACCOUNT="claude"  # Hardcoded

✅ Correct:

# 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:

[[ -z "$TOKEN" ]] && error "No token"

✅ Correct:

[[ -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:

# 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: <exact_value>
- Field2: <exact_value>

AFTER:
- Field1: <new_value> ✅ Changed
- Field2: <new_value> ✅ 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

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

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

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:

## 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:

## 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:

1. ✅ Works on different devices without modification
2. ✅ Auto-discovers common variations in setup
3. ✅ Fails gracefully with actionable error messages
4. ✅ Can be debugged by reading the error output
5. ✅ 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.