Server-side SDK for Postio — the UK validation API for addresses, emails and phone numbers. Wraps @postio/core with retries (exp backoff + full jitter) and an optional structured logger.

First time? Sign up free — first 100 lookups on us, no card needed.

If you're building in the browser, a Cloudflare Worker, Bun, or Deno — use @postio/core directly. This package is the right pick when you're calling Postio from a long-running Node server (Express, Fastify, Hono on Node, Next.js server actions, queue workers, cron jobs).

Node 20+.

Install

npm install @postio/node

Use

import { Postio } from "@postio/node";

const postio = new Postio({ apiKey: process.env.POSTIO_API_KEY! });

const search = await postio.address.search("57 wimpole");
const full = await postio.address.udprn(search.results[0]!.udprn);
const email = await postio.email.validate("alice@example.com");

The surface — connect, address.{search,postcode,udprn}, email.validate, phone.validate — is identical to @postio/core.

Retries

On by default: 2 retries, exponential backoff with full jitter, on 408 / 409 / 429 / 500 / 502 / 503 / 504 and network errors (DNS / TCP / TLS reset). 4xx error responses are NOT retried — they're programming errors that won't get better. User-aborted requests (via your own AbortSignal) are NOT retried.

Tune or disable:

new Postio({
  apiKey: "…",
  retry: { maxRetries: 5, baseDelayMs: 250, capDelayMs: 4000 },
});

new Postio({ apiKey: "…", retry: false }); // off

Default per-request timeout is 30 s (vs. 10 s in core). Override via timeoutMs. The timeout bounds total time across retries — if a single attempt is slow, retries won't overrun the budget.

Logging

Pass a single function. You'll get a structured event per attempt and per retry decision — easy to forward to pino / winston / OpenTelemetry.

new Postio({
  apiKey: "…",
  logger: (e) => console.log(`[${e.level}] ${e.msg}`, e),
});

Event shape:

{
  level: "debug" | "info" | "warn" | "error",
  msg: "postio_request_ok" | "postio_request_failed"
     | "postio_request_retrying" | "postio_request_retrying_after_error"
     | "postio_request_aborted" | "postio_request_error",
  attempt: number,        // 0 = first try
  status?: number,
  durationMs?: number,
  delayMs?: number,       // backoff sleep before next attempt
  url?: string,
  error?: unknown,
}

Errors

Same PostioError as @postio/core. Re-exported here so you don't need to install both.

import { Postio, PostioError } from "@postio/node";

try {
  await postio.address.udprn(99999999);
} catch (err) {
  if (err instanceof PostioError) {
    err.status;      // 404
    err.code;        // "udprn_not_found"
    err.requestId;   // server-side correlation id
  }
}