Keyword extraction

Top keywords and two-word phrases by frequency (stopwords removed). Send POST /api/keywords with the required field text and pay $0.002 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns a JSON object with keywords and phrases.

Cheap, deterministic signal for routing, tagging, and dedup.

Category: Text processing · Tags: keywords nlp text tagging

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/keywords \
  -H "Content-Type: application/json" \
  -d '{"text":"The x402 protocol lets an agent pay for a single request. A server answers with payment terms, the agent signs a stablecoin authorization, and the request is retried with the payment attached. Payment settles on chain, so the server needs no account and the agent needs no subscription. The x402 protocol prices each request on its own, and payment terms travel with the request itself.","limit":10}'

Without payment this returns HTTP 402 Payment Required with the exact price for keywords; any x402 v2 or MPP client pays it and retries.

Example response

{
  "keywords": [
    {
      "term": "request",
      "count": 4
    },
    {
      "term": "payment",
      "count": 4
    },
    {
      "term": "agent",
      "count": 3
    }
  ],
  "phrases": [
    {
      "term": "x402 protocol",
      "count": 2
    },
    {
      "term": "payment terms",
      "count": 2
    }
  ]
}

From an MCP client

catalog.call {
  "slug": "keywords",
  "params": {
    "text": "The x402 protocol lets an agent pay for a single request. A server answers with payment terms, the agent signs a stablecoin authorization, and the request is retried with the payment attached. Payment settles on chain, so the server needs no account and the agent needs no subscription. The x402 protocol prices each request on its own, and payment terms travel with the request itself.",
    "limit": 10
  }
}

On the hosted connector at https://agent402.tools/mcp, catalog.call runs keywords free (rate-limited, no wallet). Local install: npx -y agent402-mcp.

Errors and behavior

• text is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Free tier: no outbound network call leaves the server for this tool, so proof-of-work (16 leading zero bits of sha256) pays for it.
• A GET or HEAD to /api/keywords returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

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();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/keywords", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "text": "The x402 protocol lets an agent pay for a single request. A server answers with payment terms, the agent signs a stablecoin authorization, and the request is retried with the payment attached. Payment settles on chain, so the server needs no account and the agent needs no subscription. The x402 protocol prices each request on its own, and payment terms travel with the request itself.",
    "limit": 10
  }),
});

No wallet? Pay with compute

Fetch a challenge, solve the sha256 puzzle (16 leading zero bits, a fraction of a second of CPU), 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://agent402.tools/api/pow/challenge?slug=keywords")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/keywords", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"text":"The x402 protocol lets an agent pay for a single request. A server answers with payment terms, the agent signs a stablecoin authorization, and the request is retried with the payment attached. Payment settles on chain, so the server needs no account and the agent needs no subscription. The x402 protocol prices each request on its own, and payment terms travel with the request itself.","limit":10}) });

Part of these workflows

Keyword extraction is one step in these 4 skill packs, each sold as a single call:

• Content grade - Grade a page's content quality - extract the readable content then analyze keyword density.
• Feed watch - Monitor an RSS/Atom feed in one call: parse the feed, read the top story in full, extract the keywords driving the cycle, and diff the item list against your last run to isolate what's new.
• Text analysis - Full text analysis - word/sentence stats, keyword extraction, and token count in one pass.
• Text hygiene - Turn a wall of dirty text - chat logs, scraped pages, user-generated content, log dumps - into something safe to store, search, and pipe into the next step. Measure first, redact PII before anything else touches the data, then dedupe, sort, extract entities, surface keywords, and grade the readability of what's left.

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