diff --git a/.github/FUNDING.yml b/.github/FUNDING.yml
new file mode 100644
index 0000000..7ecc2f7
--- /dev/null
+++ b/.github/FUNDING.yml
@@ -0,0 +1 @@
+custom: "https://softpeanut.github.io/csv-preflight/support.html"
diff --git a/index.html b/index.html
index e256ec8..996ad06 100644
--- a/index.html
+++ b/index.html
@@ -1,5 +1,5 @@
 <!doctype html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>CSV Preflight — local CSV and Shopify product import checker</title><meta name="description" content="Check CSV structure locally, with an optional Shopify product CSV preset for documented headers and values. No upload or signup."><link rel="canonical" href="https://softpeanut.github.io/csv-preflight/"><meta property="og:title" content="CSV Preflight — local CSV and Shopify product import checker"><meta property="og:description" content="Check generic CSV structure or a bounded set of documented Shopify product CSV rules without uploading your data."><meta property="og:url" content="https://softpeanut.github.io/csv-preflight/"><meta property="og:type" content="website"><meta name="twitter:card" content="summary"><link rel="icon" href="logo.svg" type="image/svg+xml"><link rel="stylesheet" href="styles.css"><script type="application/ld+json">{"@context":"https://schema.org","@type":"SoftwareApplication","name":"CSV Preflight","url":"https://softpeanut.github.io/csv-preflight/","applicationCategory":"DeveloperApplication","operatingSystem":"Any","description":"Check generic CSV structure or a bounded set of documented Shopify product CSV rules locally without uploading files.","isAccessibleForFree":true,"offers":{"@type":"Offer","price":"0","priceCurrency":"USD"}}</script></head>
-<body><main><p><a href="article.html">Read: CSV Is a State Machine</a> · <a href="case-study.html">Checkable example</a> · <a href="csv-ci-case-study.html">Public CI case study</a> · <a href="ko.html" lang="ko">한국어 서비스</a></p><header><span class="eyebrow">LOCAL-ONLY CSV CHECK</span><h1>Catch import failures<br>before your importer does.</h1><p>Drop or paste CSV. Nothing leaves your browser.</p></header>
+<body><main><p><a href="article.html">Read: CSV Is a State Machine</a> · <a href="case-study.html">Checkable example</a> · <a href="csv-ci-case-study.html">Public CI case study</a> · <a href="support.html">Support the project</a> · <a href="ko.html" lang="ko">한국어 서비스</a></p><header><span class="eyebrow">LOCAL-ONLY CSV CHECK</span><h1>Catch import failures<br>before your importer does.</h1><p>Drop or paste CSV. Nothing leaves your browser.</p></header>
 <aside class="tip"><div><strong>Did the free checker save you time?</strong><span>An optional Lightning tip buys no cleanup, support, feature, or import guarantee. It is separate from the fixed-scope service.</span></div><a href="lightning:softpeanut@stacker.news">Tip 2+ sats · softpeanut@stacker.news</a></aside>
 <section id="drop" class="card drop"><input id="file" type="file" accept=".csv,text/csv"><label for="file"><strong>Drop a CSV here</strong><span>or choose a file</span></label><div class="or">OR PASTE</div><textarea id="input" placeholder="email,name&#10;ada@example.com,Ada"></textarea><div class="profile"><label for="profile">Validation profile</label><select id="profile"><option value="generic">Generic CSV structure</option><option value="shopify:create">Shopify — new products</option><option value="shopify:update">Shopify — update products</option></select><small>Shopify preset reviewed against the <a href="https://help.shopify.com/en/manual/products/import-export/using-csv" target="_blank" rel="noopener">official product CSV guide</a> on 2026-08-27. It checks a bounded set of documented rules and does not guarantee import success.</small></div><button id="check">Run preflight</button></section>
 <section id="results" class="card" hidden><div class="summary"><div><small>ENCODING</small><strong id="encoding">Pasted text</strong></div><div><small>DELIMITER</small><strong id="delimiter">Comma</strong></div><div><small>ROWS</small><strong id="rows">0</strong></div><div><small>ISSUES</small><strong id="count">0</strong></div></div><h2>Preflight report</h2><ul id="issues"></ul><div class="actions"><button id="csvDownload">Download cleaned CSV</button><button id="reportDownload" class="secondary">Download error report</button></div></section>
diff --git a/offer.test.mjs b/offer.test.mjs
index 4431601..2bc6e9b 100644
--- a/offer.test.mjs
+++ b/offer.test.mjs
@@ -29,6 +29,8 @@ const githubActionGuide = readFileSync(new URL("./validate-csv-github-actions.ht
 const ciSetupTerms = readFileSync(new URL("./ci-setup-terms.html", import.meta.url), "utf8");
 const ciSetupTermsZhCn = readFileSync(new URL("./ci-setup-terms-zh-CN.html", import.meta.url), "utf8");
 const ciSetupTemplate = readFileSync(new URL("./.github/ISSUE_TEMPLATE/ci-setup.yml", import.meta.url), "utf8");
+const supportPage = readFileSync(new URL("./support.html", import.meta.url), "utf8");
+const funding = readFileSync(new URL("./.github/FUNDING.yml", import.meta.url), "utf8");
 import { analyze, serializeCsv } from "./csv.mjs";
 
 test("presents a bounded service without pretending payment or booking is live", () => {
@@ -85,6 +87,12 @@ test("optional tips cannot be mistaken for service payment", () => {
   assert.match(koreanPage, /2 sats 이상 팁/);
   assert.match(koreanPage, /정리 작업·지원·기능·가져오기 성공을 구매하지 않습니다/);
   assert.match(koreanPage, /고정 범위 서비스와 별개입니다/);
+  assert.match(page, /support\.html/);
+  assert.match(supportPage, /lightning:softpeanut@stacker\.news/);
+  assert.match(supportPage, /buys no product, cleanup, support, feature, priority, service, guarantee, or tax receipt/);
+  assert.match(supportPage, /Do not send CSV data, credentials, contact details, or payment proof/);
+  assert.match(supportPage, /If you intend to buy a product or service, do not use this link/);
+  assert.equal(funding.trim(), 'custom: "https://softpeanut.github.io/csv-preflight/support.html"');
 });
 
 test("offers only the completed bounded offline batch product", () => {
@@ -214,6 +222,7 @@ test("publishes truthful search metadata for every public page", () => {
     "https://softpeanut.github.io/csv-preflight/validate-csv-github-actions.html",
     "https://softpeanut.github.io/csv-preflight/ci-setup-terms.html",
     "https://softpeanut.github.io/csv-preflight/ci-setup-terms-zh-CN.html",
+    "https://softpeanut.github.io/csv-preflight/support.html",
   ]) {
     assert.match(sitemap, new RegExp(`<loc>${location.replaceAll(".", "\\.")}</loc>`));
   }
diff --git a/sitemap.xml b/sitemap.xml
index 0a09aef..4d2800e 100644
--- a/sitemap.xml
+++ b/sitemap.xml
@@ -44,4 +44,8 @@
     <loc>https://softpeanut.github.io/csv-preflight/ci-setup-terms-zh-CN.html</loc>
     <lastmod>2026-08-27</lastmod>
   </url>
+  <url>
+    <loc>https://softpeanut.github.io/csv-preflight/support.html</loc>
+    <lastmod>2026-08-28</lastmod>
+  </url>
 </urlset>
diff --git a/support.html b/support.html
new file mode 100644
index 0000000..66ea677
--- /dev/null
+++ b/support.html
@@ -0,0 +1,28 @@
+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width,initial-scale=1">
+  <title>Support CSV Preflight</title>
+  <meta name="description" content="Voluntarily support the free CSV Preflight project with a Lightning tip.">
+  <link rel="canonical" href="https://softpeanut.github.io/csv-preflight/support.html">
+  <link rel="icon" href="logo.svg" type="image/svg+xml">
+  <link rel="stylesheet" href="styles.css">
+</head>
+<body>
+  <main>
+    <p><a href="./">← CSV Preflight</a></p>
+    <header>
+      <span class="eyebrow">VOLUNTARY OPEN-SOURCE SUPPORT</span>
+      <h1>Keep the free checker free.</h1>
+      <p>CSV Preflight runs without uploads, accounts, analytics, or subscriptions.</p>
+    </header>
+    <section class="card">
+      <h2>Lightning tip</h2>
+      <p><a href="lightning:softpeanut@stacker.news">softpeanut@stacker.news</a></p>
+      <p>This is an optional donation to support the open-source project. It buys no product, cleanup, support, feature, priority, service, guarantee, or tax receipt. Do not send CSV data, credentials, contact details, or payment proof.</p>
+      <p>There is no refund process for voluntary tips. If you intend to buy a product or service, do not use this link.</p>
+    </section>
+  </main>
+</body>
+</html>