Forecast (Holt-Winters seasonal)

Holt-Winters triple exponential smoothing - level + trend + seasonal component. Send POST /api/forecast-holt-winters with the required fields values and horizon and pay $0.001 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns a JSON object with method, n, horizon, period, periodSource and 5 more.

Use for series with a repeating cycle (weekly retail traffic, monthly utility usage, quarterly revenue). Additive seasonality (constant amplitude) or multiplicative (amplitude grows with level). `period` is optional - if omitted, the kit auto-detects via autocorrelation on first differences and surfaces what it picked (with the ACF strength) so you can audit. Needs at least two full seasonal cycles to fit reliably.

Category: Live public data · Tags: forecast timeseries holt-winters seasonal exponential-smoothing prediction

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/forecast-holt-winters \
  -H "Content-Type: application/json" \
  -d '{"values":[10,14,18,22,11,15,19,23,12,16,20,24],"horizon":4,"period":4}'

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

Example response

{
  "method": "holt-winters",
  "n": 12,
  "horizon": 4,
  "period": 4,
  "periodSource": "provided",
  "seasonality": "additive",
  "alpha": 0.5,
  "beta": 0.1,
  "gamma": 0.1,
  "forecast": [
    {
      "step": 1,
      "point": 12.5324,
      "lower95": 11.6958,
      "upper95": 13.369
    },
    {
      "step": 2,
      "point": 16.7253,
      "lower95": 15.5421,
      "upper95": 17.9084
    },
    {
      "step": 3,
      "point": 20.9462,
      "lower95": 19.4972,
      "upper95": 22.3952
    },
    {
      "step": 4,
      "point": 25.1831,
      "lower95": 23.5098,
      "upper95": 26.8563
    }
  ]
}

From an MCP client

catalog.call {
  "slug": "forecast-holt-winters",
  "params": {
    "values": [
      10,
      14,
      18,
      22,
      11,
      15,
      19,
      23,
      12,
      16,
      20,
      24
    ],
    "horizon": 4,
    "period": 4
  }
}

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

Errors and behavior

• values and horizon are 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/forecast-holt-winters 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/forecast-holt-winters", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "values": [
      10,
      14,
      18,
      22,
      11,
      15,
      19,
      23,
      12,
      16,
      20,
      24
    ],
    "horizon": 4,
    "period": 4
  }),
});

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=forecast-holt-winters")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/forecast-holt-winters", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"values":[10,14,18,22,11,15,19,23,12,16,20,24],"horizon":4,"period":4}) });

Part of these workflows

Forecast (Holt-Winters seasonal) is one step in this skill pack, each sold as a single call:

• Forecasting bake-off - Don't guess which forecasting method to trust. Backtest all four (naive/drift, SES, Holt, Holt-Winters) on a real series, rank by out-of-sample RMSE, then forecast forward with the winner and its 95% prediction interval. Method selection without the hand-waving.

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