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RouterClient is the main entry point in the SDK. 
import { RouterClient, createViemSigner } from "@selat-ai/router-client";

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Constructor

new RouterClient({
  chain,
  privateKey,
  signer,
  routerUrl,
  requestTimeoutMs,
  defaultHeaders
})

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Parameters

ParameterTypeRequiredDefaultDescription
chainSupportedChainNameYesNoneThe chain to settle the payment on. See Supported chains.
privateKey0x${string}NoNoneBuilds a signer inside the SDK process. Use this only when in-process private key handling is acceptable.
signerPaymentSignerNoNoneA fully constructed signer object. Use this when you want more control or want to keep secrets elsewhere.
routerUrlstringNohttps://router.selat.aiRouter base URL used to build the proxy request.
requestTimeoutMsnumberNo30000Request timeout in milliseconds for each router call.
defaultHeadersRecord<string, string>No{}Headers applied to every request before per-call overrides.
You must provide either signer or privateKey.

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Returns

Return valueTypeDescription
new RouterClient(...)RouterClient instanceCreates a client that can send paid requests through selat-router.

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Supported chains

The chain option selects the chain SELAT settles your payment on. Pass the chain key as a string (the SDK’s SupportedChainName), for example chain: "base". Payments settle in USDC over Circle Gateway, so the supported set tracks the EVM chains Circle Gateway supports, plus Arc. These keys are confirmed across the SELAT stack:
ChainKeyNotes
BasebaseDefault throughout the docs; most widely tested.
Optimismoptimism
Arbitrumarbitrum
ArcarcPrivate-access mainnet (eip155:5042). Requires raw-key signing — Circle’s MPC signer can’t sign Arc yet — and gasless (eco) funding is not available.
Base, Optimism, and Arbitrum additionally support gasless deposits into Circle Gateway via Eco — no native gas needed in the wallet, settling on Polygon. Top up with selat fund --method eco. Circle Gateway supports additional EVM mainnets. For the authoritative list your runtime actually accepts, run: 
npx @selat-ai/selat-pay --list-chains

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Methods

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fetch(input, init?)

Fetches a target URL through SELAT and returns the final response. 
const response = await client.fetch("https://upstream.example.com/v1/data", {
  method: "GET",
  preferProtocol: "mpp"
});

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Parameters

ParameterTypeRequiredDefaultDescription
inputstringYesNoneThe target URL to fetch through SELAT.
initRouterFetchOptionsNo{}Request options forwarded to the router proxy call.
preferProtocol accepts:
  • mpp
  • x402

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Request options

OptionTypeRequiredDefaultDescription
methodstringNoGETHTTP method for the target request.
headersHeadersInitNo{}Headers added to the proxied request.
bodyBodyInit | nullNoNoneRequest body for POST, PUT, PATCH, or other body-bearing methods.
signalAbortSignalNoNoneCancels the request and any retry flow.
preferProtocol"mpp" | "x402"NomppHints which paid-rail protocol to prefer.

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Returns

Return valueTypeDescription
client.fetch(...)Promise<Response>Resolves to the final upstream Response. If payment is not required, the first response is returned directly.
If the upstream response does not require payment, the SDK returns it directly.

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createFetch({ baseUrl })

Creates a fetch-like helper for relative paths. 
const apiFetch = client.createFetch({ baseUrl: "https://upstream.example.com" });

const response = await apiFetch("/v1/data");

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Parameters

ParameterTypeRequiredDefaultDescription
baseUrlstringYesNoneBase URL used to resolve relative paths before routing through SELAT.

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Returns

Return valueTypeDescription
client.createFetch(...)(path: string, init?: RouterFetchOptions) => Promise<Response>Returns a fetch-like function bound to the provided base URL.

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Errors

The main configuration and payment flow can raise these public errors:
  • RouterClientConfigError
  • QuoteParseError
Use RouterClientConfigError to catch configuration issues early, such as missing chain or missing signer input.