build-w2a-sensor

build-w2a-sensor is a skill for Claude Code from machinepulse-ai/world2agent. It costs 69 tokens per session (6,470 once invoked), scanned C, original, Apache-2.0.

A guide for building a World2Agent sensor, which listens to an outside data source and turns incoming events into signals that agents can understand.

In plain words
What is it for?
Discovering a data source, designing its signals, creating the sensor package, writing its installation instructions, and testing it against the World2Agent protocol.
Why use it?
It helps decide what data and event details matter before implementation, reducing vague signals and unnecessary settings.

Skill for Claude Code

Written for Claude Code: disable-model-invocation in frontmatter. Also seen: mentions Claude Code; built for openclaw.

Good fit Discovering a data source, designing its signals, creating the sensor package, writing its installation instructions, and testing it against the World2Agent protocol.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/machinepulse-ai/world2agent/build-w2a-sensor
About the project

World2Agent is an open protocol that gives AI agents structured, real-time information from sensors watching the real world. It is for connecting agents to interchangeable data sources through a shared schema so they can perceive events and decide what to do. The catalogue skill helps operate World2Agent with an agent runtime.

machinepulse-ai/world2agent · 1,132 stars · on GitHub · world2agent.ai

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add machinepulse-ai/world2agent --skill build-w2a-sensor
Clone the repo
git clone --depth 1 https://github.com/machinepulse-ai/world2agent

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for build-w2a-sensor

README.md
[![agentmods](https://agentmods.dev/badge/skills/machinepulse-ai/world2agent/build-w2a-sensor/github.svg)](https://agentmods.dev/skills/machinepulse-ai/world2agent/build-w2a-sensor)
Your own site
<a href="https://agentmods.dev/skills/machinepulse-ai/world2agent/build-w2a-sensor"><img src="https://agentmods.dev/badge/skills/machinepulse-ai/world2agent/build-w2a-sensor/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for build-w2a-sensor

Your own site · 80×15
<a href="https://agentmods.dev/skills/machinepulse-ai/world2agent/build-w2a-sensor"><img src="https://agentmods.dev/badge/skills/machinepulse-ai/world2agent/build-w2a-sensor.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 69 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 6,470 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 6 findings, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium Rogue Agent · line 3
    Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.
    Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
  • medium MCP Rug Pull · line 142
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
  • medium MCP Rug Pull · line 479
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
  • medium MCP Rug Pull · line 502
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
  • medium Rogue Agent · line 333
    Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.
    Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
  • medium Rogue Agent · line 375
    Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.
    Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00069 $0.06470
Opus 5.5 $0.00028 $0.02588
Sonnet 5.5 $0.00014 $0.01294
Haiku 4.5 $0.00007 $0.00647

Measured 1mo ago against content hash 57e0e458ab5b, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade C, and why

build-w2a-sensor scanned grade C with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Recursive force deletehighDestructive command

rm -rf with a variable or a broad path is one typo away from removing the wrong tree.

"clean": "rm -rf dist *.tsbuildinfo",
skills/build-w2a-sensor/SKILL.md · 511 lines

How it starts

The opening of the file, as written. The whole thing — 511 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Build a World2Agent Sensor

You are guiding a developer through designing and building a W2A sensor — a package that subscribes to an external source and emits W2ASignal per the World2Agent protocol.

Protocol reference: https://github.com/machinepulse-ai/world2agent — the schema under schema/0.1/ is authoritative for every field shape. If anything in this skill contradicts the schema, the schema wins.

Your first job is discovery, not code. Sensors that skip discovery ship either too much config (tuning knobs no one touches) or too little signal quality (vague summaries, wrong event types, missing install recipe). Both are painful to fix later.

A sensor package has two deliverables:

  1. The runtime (src/) — connects to the source, transforms incoming events into W2ASignal, calls ctx.emit().
  2. SETUP.md — the install recipe. When the consumer agent runs the host's sensor-add flow (e.g. /world2agent:sensor-add <package> in Claude Code), it reads this file, runs the Q&A defined inside, writes the sensor's entry into ~/.world2agent/config.json, and writes a per-user handler skill into the agent runtime's skills directory. The handler is generated by the install flow, not shipped in the package.

Do not scaffold until Phase 1 and Phase 2 are settled.


Phase 1 — Interrogate the source

Ask these conversationally (batch in one message, don't serialize). Adapt to what the user already said.

1. What does the sensor connect to?

Name the source platform and give the user-facing "why this matters". This drives source_type, package naming, and what domain namespace the event types use.

2. How do events reach the sensor?

Pick the highest available option — do not default to polling if a push channel exists.

Mechanism Use when Notes
Official push (webhook / SSE / WebSocket) The source offers it Preferred: seconds latency, no wasted calls, no cursor drift
Official API polling No push offered Persist a cursor via ctx.store
Schedule-triggered (cron) Source is inherently periodic (digests, daily summaries) Time itself is the trigger
File-system watch / scraping No official API at all Last resort — brittle and hard to test

Read the full file on GitHub · 511 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago First seen · 511 lines · 69 tokens per session scan C 57e0e458ab5b

Subscribe to this mod's changes

build-w2a-sensor is a skill published in the GitHub repository machinepulse-ai/world2agent (1,132 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 69 tokens to every session and 6,470 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it C with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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