Claude Code: Lock Down an Unattended Run with Permission Rules

The Stack

Tested Against

Steps

1. 1

   Write the permission rules

   Permission rules live in settings.json under permissions, with allow, deny, and ask lists plus a defaultMode. dontAsk mode runs only what your allow list permits and silently denies the rest, which is exactly what you want for a scheduled or headless run.

   cat > settings.json <<'EOF'
   {
     "permissions": {
       "defaultMode": "dontAsk",
       "allow": [
         "Read",
         "Bash(npm test)",
         "Bash(npm run lint)",
         "Bash(git status)",
         "Bash(git diff *)",
         "WebFetch(domain:docs.python.org)"
       ],
       "deny": [
         "Bash(git push *)",
         "Bash(rm *)",
         "Read(.env)",
         "Edit(.env)",
         "Edit(/secrets/**)"
       ]
     }
   }
   EOF
   echo "wrote settings.json"

2. 2

   What CI checks: the JSON parses and the deny list actually blocks the dangerous things

   CI parses the JSON, confirms defaultMode is a real mode (dontAsk, per code.claude.com/docs), checks the deny list blocks pushes, deletions, and secret files, and checks the allow list contains only scoped entries (no blanket Bash(*)). No API key needed.

   cat > checkperms.mjs <<'EOF'
   import { readFileSync } from 'node:fs';
   const cfg = JSON.parse(readFileSync('settings.json','utf8'));
   const MODES = ['default','acceptEdits','plan','auto','dontAsk','bypassPermissions'];
   const p = cfg.permissions || {};
   const deny = p.deny || [];
   const allow = p.allow || [];
   let ok = true;
   function check(label, cond){ console.log(label + ': ' + (cond ? 'yes' : 'NO')); if(!cond) ok=false; }
   check('settings.json parses', true);
   check('defaultMode is a real mode', MODES.includes(p.defaultMode));
   check('deny blocks git push', deny.some(r => r.includes('git push')));
   check('deny blocks rm', deny.some(r => r.includes('rm')));
   check('deny blocks .env', deny.some(r => r.includes('.env')));
   const dangerous = a => a === 'Bash(*)' || a.includes('rm ') || a.includes('git push');
   check('allow is scoped (no blanket Bash(*) or destructive)', allow.length > 0 && !allow.some(dangerous));
   if(!ok){ console.log('permission lockdown check FAILED'); process.exit(1); }
   console.log('permission lockdown check OK');
   EOF
   node checkperms.mjs

3. 3

   Run something with it (the model step, not checked by CI)

   A run that uses these rules invokes the model, which is non-deterministic and fenced. CI proves the rules are well-formed and block the dangerous operations; it does not run the agent.