Claude Code /loop: Poll a Deploy on a Fixed Interval

The Stack

Tested Against

Steps

1. 1

   Schedule the poll

   Inside any session, /loop schedules a prompt to re-fire on an interval while the session stays open. Intervals use s, m, h, or d. For a fixed schedule it accepts standard 5-field cron.

2. 2

   What CI checks: the cron expression is valid 5-field standard

   Before /loop schedules anything it needs a valid 5-field cron with no unsupported syntax. This validator accepts the post's examples and rejects extended syntax (L, W, ?) and name aliases (MON, JAN), exactly as the scheduler does. No model, no key.

   cat > loopcron.mjs <<'EOF'
   // Validate a 5-field standard cron the way Claude Code's /loop scheduler does.
   const ALIASES = ['MON','TUE','WED','THU','FRI','SAT','SUN','JAN','FEB','MAR','APR','MAY','JUN','JUL','AUG','SEP','OCT','NOV','DEC'];
   const OK = new Set('0123456789*/,-'.split(''));
   function validate(expr) {
     const f = expr.trim().split(' ').filter(Boolean);
     if (f.length !== 5) return 'bad field count';
     for (const field of f) {
       const U = field.toUpperCase();
       if (U.includes('L') || U.includes('W') || U.includes('?')) return 'unsupported syntax';
       if (ALIASES.some(a => U.includes(a))) return 'unsupported alias';
       if (![...field].every(c => OK.has(c))) return 'illegal char';
     }
     return 'OK';
   }
   for (const g of ['0 9 * * 1-5', '*/15 * * * *']) {
     if (validate(g) !== 'OK') { console.log('FAIL valid rejected: ' + g); process.exit(1); }
     console.log('VALID: ' + g);
   }
   for (const b of ['0 9 L * MON']) {
     const r = validate(b);
     if (r === 'OK') { console.log('FAIL bad accepted: ' + b); process.exit(1); }
     console.log('REJECTED: ' + b + ' (' + r + ')');
   }
   console.log('loop cron check OK');
   EOF
   node loopcron.mjs

3. 3

   Run the poll (the model step, not checked by CI)

   Once the cron is valid, the loop fires the prompt on each tick. That call invokes the model, so it is non-deterministic and fenced: CI never runs it and the badge never claims it.