How to Verify US Addresses in Node.js / Express

What the API returns

Every response is wrapped in a standard envelope. For verification, the Result field is a single object describing the matched address. This is a real response for 1600 Pennsylvania Ave NW:

{
  "Id": "118a23c7-d836-46af-a17f-022a3754e36c",
  "Result": {
    "inputAddress": "1600 Pennsylvania Ave NW Washington DC 20500",
    "fullAddress": "1600 Pennsylvania Ave NW, Washington, DC 20500-0005",
    "addressLine1": "1600 Pennsylvania Ave NW",
    "addressLine2": "Washington, DC 20500-0005",
    "unitType": null,
    "unitNumber": null,
    "city": "Washington",
    "stateCode": "DC",
    "county": "District Of Columbia",
    "zipCode": "20500",
    "zip4": "0005",
    "dpvConfirmation": "Y",
    "deliverableStatus": "Confirmed",
    "confidence": 0.6,
    "matchTier": "Approximate",
    "matchMode": "Speculative",
    "matchCode": {
      "houseNumber": "Matched",
      "street": "Matched",
      "unit": "NotApplicable",
      "city": "Matched",
      "state": "Matched",
      "zipCode": "Matched",
      "zip4": "Inferred"
    },
    "lastVerifiedDate": "2026-06-16T22:40:51",
    "footnotes": ["recovered: standardized via correction, not an exact match"]
  },
  "ClientSessionId": null,
  "StatusCode": 200,
  "IsError": false,
  "Errors": []
}

The fields you'll use most often:

• fullAddress - the postal-standardized address. Store this, not the user's raw input.
• deliverableStatus - a plain-English summary of deliverability (covered below). Branch your checkout on this.
• unitType / unitNumber - the confirmed apartment or suite as discrete fields (e.g. APT, 4B), or null when there is no unit. Only a postal-confirmed unit appears here.
• zip4 and county - appended for you even when the input only had a 5-digit ZIP.
• matchTier and confidence - how the match was reached. The example above is Approximate / 0.6 because speculative mode standardized the input rather than matching it verbatim - still Confirmed as deliverable.
• matchCode - a per-component breakdown (Matched / Corrected / Inferred / Unmatched / NotApplicable) so you can see exactly which fields were trusted versus fixed. (The response also carries postal routing fields - carrierRoute, deliveryPoint, elot - omitted above for brevity.)

Get your API key

1. Sign up at sthan.io and subscribe to the free Address Verification tier
2. Open your dashboard and create an API key
3. Copy the key - it looks like sthan_live_xxxxxxxxxxxxxxxx

You get the key immediately, with no approval queue. An API key is the simplest way to authenticate: you send it as a Bearer token on every request and there is no separate login step. (If you prefer a short-lived token, there is a JWT flow covered later.)

Configure the project

Keep your key out of source control by reading it from the environment. The optional dotenv package loads a local .env file:

npm install dotenv   # optional, for a local .env file

# Set the key in your shell (or a .env file)
export STHAN_API_KEY="sthan_live_xxxxxxxxxxxxxxxx"

import 'dotenv/config'; // loads .env in development (optional)

const STHAN_BASE_URL = 'https://api.sthan.io';
const STHAN_API_KEY = process.env.STHAN_API_KEY;

if (!STHAN_API_KEY) throw new Error('STHAN_API_KEY is not set');

Build the verification client

The client URL-encodes the address, calls the endpoint with the API key as a Bearer token, unwraps the envelope, and returns the Result object:

class VerificationError extends Error {}

async function verifyAddress(address, mode = 'speculative') {
  const encoded = encodeURIComponent(address.trim());
  const url = `${STHAN_BASE_URL}/v2/address-verification/usa/${encoded}?match=${mode}`;

  const res = await fetch(url, {
    headers: { Authorization: `Bearer ${STHAN_API_KEY}` },
  });
  if (!res.ok) throw new VerificationError(`HTTP ${res.status}`);

  // Envelope keys are PascalCase: { Id, Result, StatusCode, IsError, Errors }
  const envelope = await res.json();
  if (envelope.IsError) {
    throw new VerificationError((envelope.Errors || []).join(', '));
  }

  return envelope.Result; // fields inside Result are camelCase
}

That's the whole integration. One call:

const result = await verifyAddress('1600 pennsylvania ave nw washington dc 20500');

console.log(result.fullAddress);        // 1600 Pennsylvania Ave NW, Washington, DC 20500-0005
console.log(result.deliverableStatus);  // Confirmed
console.log(result.zip4);               // 0005

Choose a match mode

The match parameter controls how much typo tolerance the verifier applies. The same call supports four modes, from strictest to loosest:

If you omit match, the endpoint defaults to speculative for the widest recovery. Whichever mode you pick, the location-defining parts of the address - house number, ordinal, directional, state, and the street's core name - are never substituted. A looser mode only widens tolerance for misspellings of the same street, never a jump to a different one.

Interpret the result

deliverableStatus is the one field most integrations branch on. It collapses the raw postal DPV code into four plain values:

For richer logic, pair the status with matchCode. If matchCode.street is Corrected, you know the verifier fixed a typo and should show the user the standardized address to confirm. If confidence is below your threshold or matchTier is Speculative, treat the result as a suggestion rather than a fact.

Verify at form submit

Verification belongs on the server, at the moment the user submits - not in the browser. The API does not enable CORS for browser requests, and your API key must never reach client-side JavaScript. Here is an Express endpoint that verifies the submitted address and returns a decision the front end can act on:

import express from 'express';

const app = express();
app.use(express.json());

app.post('/checkout/address', async (req, res) => {
  const raw = (req.body.address || '').trim();
  if (!raw) {
    return res.status(400).json({ ok: false, reason: 'empty' });
  }

  let result;
  try {
    result = await verifyAddress(raw);
  } catch (err) {
    // Don't punish the user for our hiccup: accept, but mark unverified.
    return res.json({ ok: true, verified: false, standardized: raw });
  }

  const status = result.deliverableStatus;

  if (status === 'NotDeliverable') {
    return res.status(422).json({
      ok: false,
      reason: 'not_deliverable',
      message: "We couldn't confirm this address is deliverable. Please double-check it.",
    });
  }

  let warning = null;
  if (status === 'ConfirmedPrimaryOnly') {
    warning = 'We confirmed the building but not the unit - check the apartment/suite.';
  } else if (status === 'Unknown') {
    warning = "We couldn't fully confirm this address. Please make sure it's correct.";
  }

  res.json({
    ok: true,
    verified: status === 'Confirmed',
    standardized: result.fullAddress,
    unit: { type: result.unitType, number: result.unitNumber },
    zip4: result.zip4,
    warning,
  });
});

The front end sends the raw address to /checkout/address and gets back a clean, standardized string plus a yes/warn/no decision. Store standardized - the postal-formatted fullAddress - rather than the user's original text, and you've turned a guess into shippable data.

Alternative: JWT authentication

An API key is the simplest option and is all most apps need. If your security policy prefers short-lived credentials, the platform also supports a 2-step JWT flow. You call GET /Auth/Token once with your profileName and profilePassword headers, receive a token valid for up to 60 minutes, then send that token as the Bearer value on subsequent calls:

async function getToken() {
  const res = await fetch(`${STHAN_BASE_URL}/Auth/Token`, {
    headers: {
      profileName: process.env.STHAN_PROFILE_NAME,
      profilePassword: process.env.STHAN_PROFILE_PASSWORD,
    },
  });
  if (!res.ok) throw new Error(`Auth failed: HTTP ${res.status}`);

  const envelope = await res.json();
  return envelope.Result.access_token; // valid for up to 60 minutes
}

// Use the returned token as the Bearer value instead of the static key
const token = await getToken();

Everything else - the endpoint, the envelope, the parsing - stays exactly the same. Cache the token and refresh it shortly before the 60-minute expiry rather than fetching one per request.

Handle errors

Two status codes are worth handling explicitly so a hiccup never blocks a sale:

• 401 - The key or token was rejected. Check the value and, on the JWT flow, refresh and retry once.
• 429 - Rate limit reached. Back off and retry, or accept the address unverified rather than failing the checkout.

async function verifyWithRetry(address, mode = 'speculative', retries = 2) {
  for (let attempt = 0; attempt <= retries; attempt++) {
    const encoded = encodeURIComponent(address.trim());
    const url = `${STHAN_BASE_URL}/v2/address-verification/usa/${encoded}?match=${mode}`;
    const res = await fetch(url, {
      headers: { Authorization: `Bearer ${STHAN_API_KEY}` },
    });

    if (res.status === 429 && attempt < retries) {
      await new Promise(r => setTimeout(r, 2 ** attempt * 1000)); // 1s, then 2s
      continue;
    }
    if (!res.ok) throw new Error(`HTTP ${res.status}`);

    const envelope = await res.json();
    return envelope.Result;
  }
  return null;
}

The exponential back-off (1s, then 2s) is enough for transient limits. For heavier batch jobs, add a circuit breaker so one bad minute doesn't stall the whole queue.

What's next: fix addresses before they're submitted

Verification confirms an address at submit. You can stop bad addresses even earlier by helping users enter the right one in the first place: Address Autocomplete suggests complete, postal-formatted addresses as the user types, so most submissions are already clean before verification runs. Autocomplete has its own free tier of 100,000 requests/month - pairing the two (autocomplete as they type, one verification call at submit) keeps both your data and your costs in good shape. The Node.js autocomplete walkthrough is here: Address Autocomplete in Node.js / Express.

If you need to break an address into components, parse freeform input, or get latitude/longitude, the same envelope and the same fetch pattern apply across the Address Parser and Geocoding APIs - swap the path and read the same PascalCase envelope.