diff --git a/swa/app.js b/swa/app.js
index 715f979..1a83490 100644
--- a/swa/app.js
+++ b/swa/app.js
@@ -57,6 +57,7 @@ const followsStatus = document.getElementById('follows-status');
 const followsList = document.getElementById('follows-list');
 
 const postContent = document.getElementById('post-content');
+const postSubject = document.getElementById('post-subject');
 const charCount = document.getElementById('char-count');
 const postBtn = document.getElementById('post-btn');
 const postResult = document.getElementById('post-result');
@@ -770,11 +771,15 @@ postBtn.addEventListener('click', async () => {
   setPostResult(store.postDifficulty > 0 ? 'Mining proof of work…' : 'Publishing…', '');
 
   try {
-    const { content: transformedContent, tags: mentionTags } = buildMentionEvent(content);
-    const event = await createOwnEvent({ kind: 1, tags: mentionTags, content: transformedContent, difficulty: store.postDifficulty });
+    const subject = postSubject.value.trim();
+    const subjectTags = subject ? [['subject', subject]] : [];
+    const { content: transformedContent, tags: mentionTags } = buildMentionEvent(content, subjectTags.length);
+    const tags = [...subjectTags, ...mentionTags];
+    const event = await createOwnEvent({ kind: 1, tags, content: transformedContent, difficulty: store.postDifficulty });
     await publishToAll(event);
     store.addEvent(event);
     postContent.value = '';
+    postSubject.value = '';
     charCount.textContent = '0';
     setPostResult('Posted.', 'ok');
   } catch (err) {
@@ -1472,14 +1477,15 @@ function makeRenderCallbacks() {
       rerenderFeed();
       try { await publishFollowList(); } catch { /* ignore relay error */ }
     },
-    onReply: async (parentEvent, content) => {
+    onReply: async (parentEvent, content, subject) => {
       if (!store.signer) throw new Error('Generate or import a keypair first.');
       if (!isAnyConnected()) throw new Error('Connect to a relay first.');
+      const subjectTags = subject ? [['subject', subject]] : [];
       const replyTags = buildReplyTags(parentEvent, store.signer.pubkeyHex);
-      const { content: transformedContent, tags: mentionTags } = buildMentionEvent(content, replyTags.length);
+      const { content: transformedContent, tags: mentionTags } = buildMentionEvent(content, subjectTags.length + replyTags.length);
       const event = await createOwnEvent({
         kind: 1,
-        tags: [...replyTags, ...mentionTags],
+        tags: [...subjectTags, ...replyTags, ...mentionTags],
         content: transformedContent,
         difficulty: store.postDifficulty,
       });
diff --git a/swa/feedView.js b/swa/feedView.js
index 526d9bf..e1affd8 100644
--- a/swa/feedView.js
+++ b/swa/feedView.js
@@ -1,4 +1,4 @@
-import { resolveReplyTag } from './threading.js';
+import { resolveReplyTag, getSubject, adornReplySubject } from './threading.js';
 import { getEventDifficulty } from './proofOfWork.js';
 
 const OTS_VERIFY_URL = 'https://opentimestamps.org';
@@ -275,6 +275,14 @@ export function renderEvent(event, slice, callbacks) {
     actions.appendChild(deleteBtn);
   }
 
+  const subject = getSubject(event);
+  if (subject) {
+    const subjectEl = document.createElement('div');
+    subjectEl.className = 'event-subject';
+    subjectEl.textContent = subject;
+    card.appendChild(subjectEl);
+  }
+
   card.append(content, actions);
 
   const replyForm = createReplyForm(event, displayName, onReply);
@@ -316,6 +324,13 @@ function createReplyForm(parentEvent, displayName, onReply) {
   label.className = 'reply-form-label';
   label.textContent = `Replying to ${displayName}`;
 
+  const subjectInput = document.createElement('input');
+  subjectInput.type = 'text';
+  subjectInput.className = 'reply-subject-input';
+  subjectInput.placeholder = 'Subject (optional)';
+  subjectInput.maxLength = 80;
+  subjectInput.value = adornReplySubject(getSubject(parentEvent));
+
   const textarea = document.createElement('textarea');
   textarea.rows = 3;
   textarea.placeholder = 'Write your reply…';
@@ -334,7 +349,7 @@ function createReplyForm(parentEvent, displayName, onReply) {
   resultMsg.className = 'result-msg';
 
   formActions.append(submitBtn, cancelBtn, resultMsg);
-  form.append(label, textarea, formActions);
+  form.append(label, subjectInput, textarea, formActions);
 
   cancelBtn.addEventListener('click', () => {
     form.hidden = true;
@@ -351,7 +366,7 @@ function createReplyForm(parentEvent, displayName, onReply) {
     resultMsg.className = 'result-msg';
 
     try {
-      await onReply(parentEvent, content);
+      await onReply(parentEvent, content, subjectInput.value.trim());
       textarea.value = '';
       form.hidden = true;
       resultMsg.textContent = '';
@@ -457,7 +472,15 @@ export function renderReply(event, slice) {
   content.className = 'event-content';
   content.appendChild(renderMentionContent(event.content, event.tags, profiles));
 
-  card.append(meta, content);
+  const subject = getSubject(event);
+  if (subject) {
+    const subjectEl = document.createElement('div');
+    subjectEl.className = 'event-subject';
+    subjectEl.textContent = subject;
+    card.append(meta, subjectEl, content);
+  } else {
+    card.append(meta, content);
+  }
   return card;
 }
 
diff --git a/swa/index.html b/swa/index.html
index 4b47331..a9d6d56 100644
--- a/swa/index.html
+++ b/swa/index.html
@@ -243,6 +243,7 @@ <h2>Direct Messages</h2>
     <section id="post-panel" class="panel">
       <h2>Post</h2>
       <div class="field-group">
+        <input id="post-subject" type="text" placeholder="Subject (optional)" maxlength="80" autocomplete="off">
         <textarea id="post-content" rows="4" placeholder="What's on your mind?" maxlength="2000"></textarea>
         <div class="char-counter"><span id="char-count">0</span> / 2000</div>
       </div>
diff --git a/swa/style.css b/swa/style.css
index 71ba998..64554b0 100644
--- a/swa/style.css
+++ b/swa/style.css
@@ -770,6 +770,14 @@ details[open] > summary::before {
   line-height: 1.55;
 }
 
+.event-subject {
+  font-size: 0.95rem;
+  font-weight: 600;
+  color: var(--text);
+  margin-bottom: 0.25rem;
+  word-break: break-word;
+}
+
 .mention {
   color: var(--accent);
   font-weight: 500;
diff --git a/swa/threading.js b/swa/threading.js
index 0488b75..30eac95 100644
--- a/swa/threading.js
+++ b/swa/threading.js
@@ -31,6 +31,15 @@ export function buildQuoteTag(quotedEvent, relayHint = '') {
   return ['q', quotedEvent.id, relayHint, quotedEvent.pubkey];
 }
 
+export function getSubject(event) {
+  return event.tags.find(t => t[0] === 'subject')?.[1] || '';
+}
+
+export function adornReplySubject(subject) {
+  if (!subject) return '';
+  return /^re:/i.test(subject) ? subject : `Re: ${subject}`;
+}
+
 export function buildMentionEvent(content, tagOffset = 0, eventIds = new Set()) {
   const mentionTags = [];
   const seen = new Map();
diff --git a/swa/threading.test.js b/swa/threading.test.js
index b697147..1b5f05c 100644
--- a/swa/threading.test.js
+++ b/swa/threading.test.js
@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { resolveReplyTag, buildReplyTags, buildMentionEvent, buildQuoteTag } from './threading.js';
+import { resolveReplyTag, buildReplyTags, buildMentionEvent, buildQuoteTag, getSubject, adornReplySubject } from './threading.js';
 
 const HEX_A = 'a'.repeat(64);
 const HEX_B = 'b'.repeat(64);
@@ -195,3 +195,39 @@ test('buildQuoteTag: includes provided relay hint', () => {
   const tag = buildQuoteTag(quoted, 'wss://relay.example.com');
   assert.deepEqual(tag, ['q', HEX_A, 'wss://relay.example.com', HEX_B]);
 });
+
+// ── getSubject (NIP-14) ───────────────────────────────────────────────────────
+
+test('getSubject: returns the subject tag value', () => {
+  assert.equal(getSubject({ tags: [['subject', 'Hello world']] }), 'Hello world');
+});
+
+test('getSubject: returns empty string when no subject tag', () => {
+  assert.equal(getSubject({ tags: [['e', HEX_A]] }), '');
+});
+
+test('getSubject: returns empty string for empty tags', () => {
+  assert.equal(getSubject({ tags: [] }), '');
+});
+
+test('getSubject: returns the first subject tag when several exist', () => {
+  assert.equal(getSubject({ tags: [['subject', 'first'], ['subject', 'second']] }), 'first');
+});
+
+// ── adornReplySubject (NIP-14) ────────────────────────────────────────────────
+
+test('adornReplySubject: returns empty string for empty input', () => {
+  assert.equal(adornReplySubject(''), '');
+});
+
+test('adornReplySubject: prepends "Re: " to a plain subject', () => {
+  assert.equal(adornReplySubject('Lunch plans'), 'Re: Lunch plans');
+});
+
+test('adornReplySubject: leaves an already-prefixed subject unchanged', () => {
+  assert.equal(adornReplySubject('Re: Lunch plans'), 'Re: Lunch plans');
+});
+
+test('adornReplySubject: treats the prefix case-insensitively', () => {
+  assert.equal(adornReplySubject('RE: Lunch plans'), 'RE: Lunch plans');
+});