# HALOWERK Browser Evidence — Headless Assertion Checker

> HALOWERK Browser Evidence — Headless Assertion Checker is a paid API for AI agents from lauf.halowerk.com, paid per call via x402, $0.018/call, status unknown (last checked 2026-10-12).

Loads a public HTTPS page in a headless browser, optionally waits or waits for selectors, then asserts whether specified DOM elements exist and contain expected text

## Facts

- Endpoint: POST https://lauf.halowerk.com/v1/browser-evidence?utm_source=zero.xyz
- Price: $0.018/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/halowerk-browser-evidence-headless-assertion-checker-5092cf5d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_4_LBPnHrTTv720ZD0NqHg

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability halowerk-browser-evidence-headless-assertion-checker-5092cf5d -d '<json body>'
```

Example prompt: Can you check the live page at https://example.com/status, wait up to 1500ms for the selector '#status-banner' to appear, and then assert that the element '.status-label' contains the text 'All systems operational'?

## When to prefer this

Choose this endpoint when you need cryptographically-grounded or third-party-verified evidence that a specific CSS element exists and contains expected text on a live public HTTPS page, using a real headless browser rather than a simple HTTP fetch. Prefer it over plain HTTP scrapers when the page renders content via JavaScript or requires waiting for dynamic elements. Avoid it for pages behind authentication, CAPTCHAs, or for bulk crawling entire sites.

## Known failure modes

- URL does not match https:// pattern or exceeds 2048 characters — request rejected with validation error
- Selector not found in DOM after wait steps — assertion fails with element-not-found result
- Page fails to load or returns a non-2xx status — request fails with load error
- CAPTCHA or login wall encountered — endpoint refuses and returns an error
- Wait step ms value exceeds 2000 or step count exceeds 4 — request rejected
- More than 10 assertions or 0 assertions provided — request rejected with validation error
- Page is disallowed by robots.txt — endpoint refuses to load it

## How this service works

HALOWERK laufwerk — bezahlte Endpunkte nach x402. Preise in USDC auf Base Mainnet.

## Output

Returns structured assertion results for each specified selector, indicating whether the element was found in the DOM and whether its text content matches the expected string, providing browser-based evidence of page state at the time of the request.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "pattern": "^https://[^@\\s]+$",
   "maxLength": 2048
  },
  "steps": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "action"
    ],
    "properties": {
     "ms": {
      "type": "integer",
      "maximum": 2000,
      "minimum": 0
     },
     "action": {
      "enum": [
       "wait",
       "wait_for_selector"
      ]
     },
     "selector": {
      "type": "string",
      "maxLength": 200
     }
    },
    "additionalProperties": false
   },
   "maxItems": 4
  },
  "assertions": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "selector"
    ],
    "properties": {
     "selector": {
      "type": "string",
      "maxLength": 200,
      "minLength": 1
     },
     "text_includes": {
      "type": "string",
      "maxLength": 500
     }
    },
    "additionalProperties": false
   },
   "maxItems": 10,
   "minItems": 1
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/halowerk-browser-evidence-headless-assertion-checker-5092cf5d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from lauf.halowerk.com](https://www.zero.xyz/host/lauf.halowerk.com/llms.txt)