diff --git a/bin/check-nomad-badge.ts b/bin/check-nomad-badge.ts
new file mode 100644
index 0000000..e1a86de
--- /dev/null
+++ b/bin/check-nomad-badge.ts
@@ -0,0 +1,11 @@
+#!/usr/bin/env -S node --trace-warnings --loader ts-node/esm
+
+import { checkNomadBadge } from "../lib/check-nomad-badge.js";
+
+async function main() {
+  const args = process.argv.slice(2);
+
+  await checkNomadBadge();
+}
+
+main().catch((err) => console.error(new Date(), "ERROR:", err));
diff --git a/handlers/check-nomad-badge.ts b/handlers/check-nomad-badge.ts
new file mode 100644
index 0000000..faf3aab
--- /dev/null
+++ b/handlers/check-nomad-badge.ts
@@ -0,0 +1,26 @@
+import { Context, APIGatewayProxyResult, APIGatewayEvent } from "aws-lambda";
+import { checkNomadBadge } from "../lib/check-nomad-badge.js";
+
+export const handler = async (
+  event: APIGatewayEvent & {
+    campaignTagIds?: number[];
+    campaignBegins?: Date | string;
+    campaignEnds?: Date | string;
+  },
+  context: Context
+): Promise<APIGatewayProxyResult> => {
+  console.log(`Event: %o`, event);
+  console.log(`Context: %o`, context);
+
+  const { campaignTagIds, campaignBegins, campaignEnds } = event;
+  const retBadges = await checkNomadBadge({
+    campaignTagIds,
+    campaignBegins,
+    campaignEnds,
+  });
+
+  return {
+    statusCode: 200,
+    body: JSON.stringify({ message: "done.", retBadges }),
+  };
+};
diff --git a/lib/check-nomad-badge.ts b/lib/check-nomad-badge.ts
new file mode 100644
index 0000000..431105f
--- /dev/null
+++ b/lib/check-nomad-badge.ts
@@ -0,0 +1,111 @@
+import { sql, sqlSIW } from "../lib/db.js";
+
+const MATTERS_CAMPAIGN_BEGINS =
+  process.env.MATTERS_CAMPAIGN_BEGINS || "2023-11-14T16:00:00.000Z"; // 00:00 in UTC+8
+const MATTERS_CAMPAIGN_ENDS =
+  process.env.MATTERS_CAMPAIGN_ENDS || "2024-01-14T15:59:59.999Z";
+
+const ARRAY_TYPE = 1009; // Postgres internal value shouldn't be here;
+
+export async function checkNomadBadge({
+  campaignTagIds = [157201], // https://matters.town/tags/157201-nomadmatters?type=latest
+  campaignBegins,
+  campaignEnds,
+}: {
+  campaignTagIds?: number[];
+  campaignBegins?: Date | string;
+  campaignEnds?: Date | string;
+} = {}): Promise<any> {
+  // const [{ version, now }] = await sql` SELECT VERSION(), NOW() `; console.log("pgres:", { version, now });
+
+  if (!campaignBegins) campaignBegins = new Date(MATTERS_CAMPAIGN_BEGINS);
+  if (!campaignEnds) campaignEnds = new Date(MATTERS_CAMPAIGN_ENDS);
+  // const nomadTagId = 157201; // https://matters.town/tags/157201-nomadmatters?type=latest
+
+  const referrals = await sql`-- select all referred users
+SELECT extra->>'referralCode' AS "referralCode", COUNT(*) ::int
+FROM public.user
+WHERE created_at BETWEEN ${campaignBegins} AND ${campaignEnds}
+  AND extra->'referralCode' IS NOT NULL
+GROUP BY 1
+HAVING COUNT(*) >=5
+ORDER BY count DESC -- LIMIT 13 `;
+  console.log("log user by referrals:", referrals);
+  const referralsMap = new Map<string, number>(
+    referrals.map(({ referralCode, count }) => [referralCode, count])
+  );
+
+  const allApplicants = await sql`-- query all campaign applicants
+SELECT * FROM (
+  SELECT DISTINCT ON (author_id)
+    user_name, display_name, author_id ::int, article.id ::int, article.title, article.created_at,
+    (ub.extra->'level')::int AS level -- current nomad badge level
+  FROM article_tag
+  LEFT JOIN public.article ON article_id=article.id
+  LEFT JOIN public.user u ON author_id=u.id
+  LEFT JOIN public.user_badge ub ON user_id=u.id AND ub.type='nomad'
+  WHERE created_at BETWEEN ${campaignBegins} AND ${campaignEnds}
+    AND tag_id =ANY(${campaignTagIds})
+  ORDER BY author_id, article.created_at DESC
+) t
+ORDER BY created_at DESC ; `;
+
+  console.log("consider all applicants:", allApplicants);
+
+  const newNomadBadges: Array<{
+    userId: string | number;
+    type: string;
+    extra: any;
+  }> = [];
+  allApplicants.forEach(({ userName, authorId, level: currentLevel }) => {
+    const referralCount = referralsMap.get(userName) || 0;
+
+    let level: number;
+    if (referralCount >= 20) level = 4;
+    else if (referralCount >= 10) level = 3;
+    else if (referralCount >= 5) level = 2;
+    else level = 1;
+
+    if (currentLevel >= level) {
+      // skip if there's existing level override
+      return;
+    }
+
+    newNomadBadges.push({
+      userId: authorId,
+      type: "nomad",
+      extra: { level },
+    });
+  });
+
+  console.log("consider new nomad badges:", newNomadBadges);
+  if (newNomadBadges.length === 0) return;
+
+  const retBadges = await sqlSIW`-- upsert all new badges
+INSERT INTO public.user_badge AS ub(user_id, type, extra)
+  SELECT * FROM UNNEST(
+    ${sqlSIW.array(
+      newNomadBadges.map(({ userId }) => userId),
+      ARRAY_TYPE
+    )} ::int[],
+    ${sqlSIW.array(
+      newNomadBadges.map(({ type }) => type),
+      ARRAY_TYPE
+    )} ::text[],
+    ${sqlSIW.array(
+      newNomadBadges.map(({ extra }) => JSON.stringify(extra)),
+      ARRAY_TYPE
+    )} ::jsonb[]
+  )
+ON CONFLICT (user_id, type)
+DO UPDATE
+  SET extra=((COALESCE(ub.extra, '{}' ::jsonb) - ${[
+    "removeKeys",
+  ]} ::text[]) || EXCLUDED.extra)
+RETURNING * ;
+`;
+
+  console.log("upsert'ed new badges:", retBadges);
+
+  return retBadges;
+}