Pollers

Pollers — Event-Driven Monitoring

Pollers are lightweight scripts that check external services on a schedule and report back when something needs attention. They live inside skills and are discovered automatically by the scheduler.

How It Works

1. A skill includes a pollers.json file alongside its SKILL.md
2. The scheduler discovers all pollers.json files at startup and when reload_pollers is called
3. On each cron tick, the scheduler runs the poller command as a subprocess
4. Each line of stdout is parsed as JSON and delivered to the agent as an event
5. If there's nothing to report, the poller outputs nothing — silence is the filter

Creating a Poller

1. Write the poller script

The script runs in the skill directory. It receives these environment variables automatically:

| Variable | Description | |----------|-------------| | STATE_DIR | The skill directory (writable, for cursors/state) | | POLLER_NAME | The poller's name from pollers.json |

Plus any custom env vars from the env field, plus the agent's existing environment.

Output contract:

• stdout: JSONL (one JSON object per line). Each line must have poller (string) and prompt (string) fields.
• stderr: Free-form logging. Not forwarded to the agent.
• Exit 0: Success. Non-zero: Error, this cycle is skipped.

Example poller script:

#!/usr/bin/env python3
"""Check for new items since last poll."""
import json, os, sys
from pathlib import Path

STATE_DIR = Path(os.environ.get("STATE_DIR", "."))
CURSOR_FILE = STATE_DIR / "cursor.json"

def load_cursor():
    if CURSOR_FILE.exists():
        return json.loads(CURSOR_FILE.read_text())
    return {}

def save_cursor(cursor):
    CURSOR_FILE.write_text(json.dumps(cursor, indent=2))

def main():
    cursor = load_cursor()
    # ... check your service, compare against cursor ...

    new_items = []  # your logic here

    for item in new_items:
        event = {
            "poller": os.environ.get("POLLER_NAME", "my-poller"),
            "prompt": f"New item: {item['title']}"
        }
        print(json.dumps(event))

    # Update cursor so next run skips these items
    save_cursor(cursor)

if __name__ == "__main__":
    main()

2. Create pollers.json in the skill directory

{
  "pollers": [
    {
      "name": "my-service-check",
      "command": "python poller.py",
      "cron": "*/5 * * * *",
      "env": {
        "SERVICE_URL": "https://example.com/api"
      }
    }
  ]
}

Top-level must be a dict with a pollers key (not a bare array).

| Field | Required | Description | |-------|----------|-------------| | name | yes | Unique identifier. Used in logs and event routing. | | command | yes | Shell command, relative to the skill directory. | | cron | yes | Cron expression (5-field, UTC). | | env | no | Additional environment variables for the script. |

3. Register the pollers

After creating or updating pollers.json, call the reload_pollers tool. This re-scans all skill directories and registers any new pollers with the scheduler.

reload_pollers()
# → "Reloaded. 2 poller(s) registered: bluesky-mentions, github-issues"

Pollers are also loaded automatically at startup.

File Layout

skills/my-monitor/
├── SKILL.md
├── pollers.json        ← declares pollers
├── poller.py           ← the script
├── cursor.json         ← poller state (managed by script)
└── events.jsonl        ← optional local event log

Design Patterns

See [design-patterns.md](design-patterns.md) for detailed guidance on:

• State management — cursor pattern, timestamp vs URI cursors, external service state, recovery on first run
• Filtering — selecting actionable notification types, avoiding shared is_read traps
• Prompt quality — including URIs/CIDs so the agent can act, not just observe
• Error handling — fail silently (exit non-zero), never emit on error
• Anti-patterns — common mistakes and how to avoid them

Security & Privacy

See [security.md](security.md) for guidance on:

• Trust tiers — the follow-gate pattern for sorting trusted vs unknown sources
• Operator in the loop — keeping the human informed without locking everything down
• Credential handling — env vars, per-agent accounts, what not to log
• Prompt injection — honest reporting with context, not sanitization

Key Constraints

• 60-second timeout. If a poller doesn't finish in 60s, it's killed and the cycle is skipped.
• Silence means nothing to report. Only output lines when there's something actionable.
• One JSON object per line. Each line must parse independently.
• poller and prompt are required fields. Lines missing either are dropped.
• Pollers are dumb. No LLM calls. Check a service, output what changed, exit. Keep them fast and pure.
• State management is the poller's job. Use STATE_DIR to store cursors, history, or any persistent state. The scheduler doesn't track state for you.

Debugging

If a poller isn't working:

1. Check it was discovered: reload_pollers reports the count and names
2. Run it manually: cd skills/my-monitor && STATE_DIR=. POLLER_NAME=test python poller.py
3. Check stderr: Poller stderr is logged as poller_stderr events
4. Check exit code: Non-zero exits are logged as poller_nonzero_exit
5. Check JSON format: Each stdout line must be valid JSON with poller and prompt keys

Available Tool

| Tool | Description | |------|-------------| | reload_pollers | Re-scan all skills/*/pollers.json and register pollers. Call after installing/updating skills. |

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: tkellogg
• Source: tkellogg/open-strix
• License: MIT

Install and usage instructions live in the source repository linked above.