Headless Cron Creator Skill for Claude

Headless Cron Creator Skill

Generate headless Claude Code cron jobs from a task description and schedule. Creates a wrapper script with safety mechanisms (lockfile, budget cap, dry-run default, logging) and installs crontab entries. All crontab mutations go through scripts/crontab-manager.py, which writes to temp files and creates timestamped backups in ~/.claude/crontab-backups/ before every change -- never pipe directly to crontab - because a mid-stream pipe failure wipes the entire crontab.

Instructions

Phase 1: PARSE

Extract job parameters from the user's request.

Required parameters:

• name -- short kebab-case identifier (e.g., reddit-automod, feed-health-check)
• prompt -- what Claude should do each run (natural language)
• schedule -- cron expression or human-readable interval

Optional parameters (with defaults):

• workdir -- where to cd before running (default: current repo root)
• budget -- max USD per run (default: 2.00; user may override)
• allowed-tools -- which tools the headless session can use (default: Bash Read; user may override)
• logdir -- where to store logs (default: {workdir}/cron-logs/{name})

Human-readable schedule conversion -- use off-minutes (7, 23, 47) instead of :00/:30 because every cron job on the system fires at round minutes, creating load spikes:

| Human Input | Cron Expression |

|-------------|----------------|

| every 12 hours | 7 */12 * * * |

| twice daily | 7 8,20 * * * |

| hourly | 23 * * * * |

| daily at 6am | 7 6 * * * |

| weekly on sunday | 7 9 * * 0 |

| every 30 minutes | */30 * * * * |

Gate: All required parameters extracted. Proceed to Phase 2.

Phase 2: GENERATE

Create the wrapper script using crontab-manager.py generate-wrapper. Embed the prompt via bash heredoc to avoid escaping issues.

python3 ~/.claude/scripts/crontab-manager.py generate-wrapper \
  --name "{name}" \
  --prompt "{prompt}" \
  --schedule "{schedule}" \
  --workdir "{workdir}" \
  --budget "{budget}" \
  --allowed-tools "{allowed_tools}"

Review the generated script. Verify it contains:

• [ ] set -euo pipefail
• [ ] flock lockfile -- prevents concurrent runs of the same job
• [ ] --permission-mode auto -- never use --dangerously-skip-permissions (auto is sufficient) or --bare (breaks OAuth/keychain auth)
• [ ] --max-budget-usd -- caps spend per run (default 2.00 USD)
• [ ] --no-session-persistence
• [ ] --allowedTools
• [ ] tee to per-run timestamped log file
• [ ] Dry-run/execute toggle -- scripts do nothing destructive without --execute
• [ ] Exit code propagation via PIPESTATUS[0]

Do not use the CronCreate tool -- it is session-scoped (dies when the session ends, auto-expires after 7 days). Use system crontab via crontab-manager.py instead.

Gate: Script generated and reviewed. Proceed to Phase 3.

Phase 3: VALIDATE

Verify the generated script meets cron best practices.

• Run the script in dry-run mode:

   bash -n scripts/{name}-cron.sh  # syntax check

• Run cron-job-auditor checks:
• [ ] Error handling (set -e)
• [ ] Lock file (flock)
• [ ] Logging (tee, LOG_DIR)
• [ ] Working directory (absolute cd)
• [ ] PATH awareness (absolute path to claude -- cron has minimal PATH, so all commands must use absolute paths)
• [ ] Cleanup on exit (lock release)

Gate: All checks pass. Proceed to Phase 4.

Phase 4: INSTALL

Install the crontab entry. Every entry gets a # claude-cron: <tag> marker so crontab-manager.py can identify and manage only its own entries without touching non-Claude crontab lines. All paths in the crontab entry must be absolute because cron has minimal PATH.

• Show the proposed entry:

   python3 ~/.claude/scripts/crontab-manager.py add \
     --tag "{name}" \
     --schedule "{schedule}" \
     --command "{absolute_script_path} --execute >> {logdir}/cron.log 2>&1" \
     --dry-run

• Ask the user for confirmation before installing. Never install without explicit approval.

• If confirmed:

   python3 ~/.claude/scripts/crontab-manager.py add \
     --tag "{name}" \
     --schedule "{schedule}" \
     --command "{absolute_script_path} --execute >> {logdir}/cron.log 2>&1"

• Verify:

   python3 ~/.claude/scripts/crontab-manager.py verify --tag "{name}"

Gate: Entry installed and verified. Proceed to Phase 5.

Phase 5: REPORT

Summarize the created cron job and print the exact commands to test and manage it.

Output:

• Script path
• Cron schedule (human-readable + expression)
• Log directory
• Budget per run
• Tag for management
• Commands for future management:

  python3 ~/.claude/scripts/crontab-manager.py list          # see all claude cron jobs
  python3 ~/.claude/scripts/crontab-manager.py verify --tag {name}  # health check
  python3 ~/.claude/scripts/crontab-manager.py remove --tag {name}   # uninstall

To modify an existing wrapper script, regenerate it with --force rather than editing in place.

Error Handling

Error: "tag already exists"

Cause: A cron entry with this tag is already installed.

Solution: Either remove --tag {name} first, or choose a different name.

Error: "claude: command not found" in cron

Cause: Cron has minimal PATH; claude isn't in it.

Solution: generate-wrapper resolves the absolute path to claude at generation time.

If the path changes, regenerate the wrapper with --force.

Error: "crontab install failed"

Cause: System crontab service issue.

Solution: Check crontab -l manually. Restore from ~/.claude/crontab-backups/.

References

• scripts/crontab-manager.py -- all crontab mutations (add, remove, list, verify, generate-wrapper)
• skills/infrastructure/cron-job-auditor/SKILL.md -- validation checks for generated scripts