HTML select

FREE with proof-of-work · or $0.001 in USDC · POST /api/html-select

Run a CSS selector against an HTML string and return the matches (text, attrs, and optionally outerHTML for each). The deterministic alternative to regex when you already have the HTML and know the selector - pairs with /api/render or any page you've fetched yourself.

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Input

Field	Type	Description
`html` *	string	Raw HTML string to query (max 5MB)
`selector` *	string	CSS selector (e.g. "h1", ".price", "article > p:first-of-type")
`limit`	number	Max matches to return, 1-200 (default 25)
`attr`	string	When set, return only this attribute's value per match (e.g. "href", "data-id") - keeps responses compact
`includeHtml`	boolean	Include outerHTML of each match (default false - text + attrs only)

Example output

{
  "count": 2,
  "matches": [
    {
      "text": "One",
      "attrs": {}
    },
    {
      "text": "Two",
      "attrs": {}
    }
  ]
}

Try it - see the 402 challenge (free)

curl -i -X POST https://base-sentinel-production.up.railway.app/api/html-select \
  -H "Content-Type: application/json" \
  -d '{"html":"<html><body><h1>One</h1><h1>Two</h1></body></html>","selector":"h1","limit":25}'

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://base-sentinel-production.up.railway.app/api/html-select", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "html": "<html><body><h1>One</h1><h1>Two</h1></body></html>",
    "selector": "h1",
    "limit": 25
  }),
});

No wallet? Pay with compute

This is a pure-CPU tool, so an agent without a wallet can pay with proof-of-work instead of USDC: fetch a challenge, solve the sha256 puzzle (16 leading zero bits - a fraction of a second of CPU, no money, no AI tokens), and resend with the X-Pow-Solution header.

import { createHash } from "node:crypto";
const lz = (b) => { let t = 0; for (const x of b) { if (!x) { t += 8; continue; } t += Math.clz32(x) - 24; break; } return t; };
const c = await (await fetch("https://base-sentinel-production.up.railway.app/api/pow/challenge?slug=html-select")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://base-sentinel-production.up.railway.app/api/html-select", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"html":"One
Two
","selector":"h1","limit":25}) });

Part of these workflows

This tool is one step in a curated multi-tool workflow - agents can fetch the whole sequence as an MCP prompt or call https://base-sentinel-production.up.railway.app/api/skill-packs/{slug}/prompt.

Structured scrape - Pull structured data out of any web page deterministically - articles to clean text, tables to JSON rows, specific elements via CSS selector - without writing regex against raw HTML.

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