diff --git a/backend/app/api/extension.py b/backend/app/api/extension.py
index 5266d46..b917882 100644
--- a/backend/app/api/extension.py
+++ b/backend/app/api/extension.py
@@ -57,6 +57,24 @@ def _sha256(path: Path) -> str:
     return h.hexdigest()
 
 
+@extension_bp.route("/probe", methods=["GET"])
+async def probe_source():
+    """Read-only resolution of a creator-page URL: tells the extension
+    whether this URL is already a Source, is for an Artist that exists
+    but with a different URL, is brand new, or doesn't match any known
+    platform pattern. Drives the content-script chip's color/copy
+    BEFORE the operator clicks, so the button can show 'already added'
+    without requiring an add-attempt."""
+    url = (request.args.get("url") or "").strip()
+    if not url:
+        return _bad("invalid_body", detail="url query parameter is required")
+    async with get_session() as session:
+        if not await _ext_key_required(session):
+            return _bad("unauthorized", status=401)
+        result = await ExtensionService(session).probe(url)
+    return jsonify(result)
+
+
 @extension_bp.route("/quick-add-source", methods=["POST"])
 async def quick_add_source():
     body = await request.get_json(silent=True)
diff --git a/backend/app/services/extension_service.py b/backend/app/services/extension_service.py
index ce34ed9..4c138de 100644
--- a/backend/app/services/extension_service.py
+++ b/backend/app/services/extension_service.py
@@ -86,6 +86,67 @@ class ExtensionService:
             "created_artist": created_artist,
         }
 
+    async def probe(self, url: str) -> dict:
+        """Read-only resolution of a creator-page URL against the FC DB.
+        Returns one of:
+          - {state: 'unknown_platform'}            — URL didn't match any
+            platform's strict artist-page pattern
+          - {state: 'new',          platform, slug} — would create both
+            artist and source on quick-add
+          - {state: 'artist_match', platform, slug, artist}
+                                                   — artist exists, this
+            exact URL isn't a Source yet (collapses the sidecar-synthetic
+            case too — the synthetic anchor counts as an existing artist
+            row but not as a pollable Source for this URL)
+          - {state: 'source_match', platform, slug, artist, source}
+                                                   — exact (artist, platform,
+            url) Source already exists
+
+        Side-effect-free: two SELECTs at most.
+        """
+        try:
+            platform, raw_slug = self._derive(url)
+        except (UnknownPlatformError, InvalidUrlError):
+            return {"state": "unknown_platform"}
+
+        slug = slugify(raw_slug)
+        artist = (await self.session.execute(
+            select(Artist).where(Artist.slug == slug)
+        )).scalar_one_or_none()
+        if artist is None:
+            return {"state": "new", "platform": platform, "slug": slug}
+
+        artist_payload = {"id": artist.id, "name": artist.name, "slug": artist.slug}
+
+        source = (await self.session.execute(
+            select(Source).where(
+                Source.artist_id == artist.id,
+                Source.platform == platform,
+                Source.url == url,
+            )
+        )).scalar_one_or_none()
+        if source is None:
+            return {
+                "state": "artist_match",
+                "platform": platform,
+                "slug": slug,
+                "artist": artist_payload,
+            }
+
+        return {
+            "state": "source_match",
+            "platform": platform,
+            "slug": slug,
+            "artist": artist_payload,
+            "source": {
+                "id": source.id,
+                "artist_id": source.artist_id,
+                "platform": source.platform,
+                "url": source.url,
+                "enabled": source.enabled,
+            },
+        }
+
     def _derive(self, url: str) -> tuple[str, str]:
         if not isinstance(url, str) or not url.strip():
             raise InvalidUrlError("url is empty")
diff --git a/extension/background/background.js b/extension/background/background.js
index 988647a..a19c900 100644
--- a/extension/background/background.js
+++ b/extension/background/background.js
@@ -259,6 +259,29 @@ browser.runtime.onMessage.addListener(async (msg) => {
         return { error: e.message };
       }
 
+    case 'PROBE_SOURCE':
+      try {
+        return await api.probeSource(msg.url);
+      } catch (e) {
+        return { error: e.message };
+      }
+
+    case 'OPEN_ARTIST_PAGE': {
+      // apiUrl is configured with the /api suffix (see
+      // options/options.html placeholder); the SPA artist route is
+      // /artist/:slug, served from the same origin. Strip /api so the
+      // browser-level URL hits the Vue router, not the JSON API.
+      const base = (api.baseUrl || '').replace(/\/+$/, '').replace(/\/api$/, '');
+      const slug = encodeURIComponent(msg.slug || '');
+      if (!base || !slug) return { error: 'apiUrl or slug missing' };
+      try {
+        await browser.tabs.create({ url: `${base}/artist/${slug}` });
+        return { success: true };
+      } catch (e) {
+        return { error: e.message };
+      }
+    }
+
     default:
       return { error: `Unknown message type: ${msg.type}` };
   }
diff --git a/extension/content/content-script.css b/extension/content/content-script.css
index d55243f..2818651 100644
--- a/extension/content/content-script.css
+++ b/extension/content/content-script.css
@@ -5,11 +5,26 @@
   background: rgb(20, 23, 26); color: rgb(244, 186, 122);
   font: 500 14px/1.2 system-ui, sans-serif;
   box-shadow: 0 4px 16px rgba(0, 0, 0, 0.4); cursor: pointer;
-  transition: transform 100ms ease;
+  transition: transform 100ms ease, background 150ms ease, color 150ms ease;
 }
 .fc-add-source-btn:hover { transform: translateY(-1px); }
 .fc-add-source-btn:disabled { opacity: 0.6; cursor: wait; }
 
+/* state colors map to the FC palette: parchment-on-slate base,
+   accent-orange for new, sage for already-subscribed, amber-warning for
+   artist-exists-but-source-missing. All readable on the dark base. */
+.fc-add-source-btn--new {
+  background: rgb(20, 23, 26); color: rgb(244, 186, 122);
+}
+.fc-add-source-btn--artist-match {
+  background: rgb(28, 23, 16); color: rgb(255, 200, 120);
+  border: 1px solid rgb(180, 130, 60);
+}
+.fc-add-source-btn--source-match {
+  background: rgb(18, 28, 20); color: rgb(140, 220, 160);
+  border: 1px solid rgb(80, 160, 100);
+}
+
 .fc-toast {
   all: revert;
   position: fixed; bottom: 84px; right: 24px; z-index: 2147483647;
diff --git a/extension/content/content-script.js b/extension/content/content-script.js
index 51154b0..780dfb5 100644
--- a/extension/content/content-script.js
+++ b/extension/content/content-script.js
@@ -2,6 +2,10 @@
   if (window.__fc_addsource_injected) return;
   window.__fc_addsource_injected = true;
 
+  // Cached probe result for the current URL so click-handlers know which
+  // action to dispatch without round-tripping again.
+  let currentProbe = null;
+
   evaluate();
 
   const reEval = () => evaluate();
@@ -9,38 +13,116 @@
   const origPush = history.pushState;
   history.pushState = function () { origPush.apply(this, arguments); reEval(); };
 
-  function evaluate() {
-    const platform = getPlatformFromUrl(window.location.href);
-    const onArtist = platform && isArtistPage(window.location.href, platform);
-    let btn = document.getElementById('fc-add-source-btn');
-    if (onArtist && !btn) injectButton();
-    else if (!onArtist && btn) btn.remove();
+  async function evaluate() {
+    const url = window.location.href;
+    const platform = getPlatformFromUrl(url);
+    const onArtist = platform && isArtistPage(url, platform);
+    const btn = document.getElementById('fc-add-source-btn');
+    if (!onArtist) {
+      if (btn) btn.remove();
+      currentProbe = null;
+      return;
+    }
+    // On artist pages, ask the backend what state the URL is in BEFORE
+    // injecting the button — so the chip can render the right state on
+    // first paint instead of flashing the generic "Add" copy and
+    // updating afterwards.
+    let probe;
+    try {
+      probe = await browser.runtime.sendMessage({ type: 'PROBE_SOURCE', url });
+    } catch (e) {
+      probe = { error: e?.message || 'probe failed' };
+    }
+    currentProbe = probe;
+    if (probe?.state === 'unknown_platform') {
+      if (btn) btn.remove();
+      return;
+    }
+    renderButton(probe);
   }
 
-  function injectButton() {
-    const btn = document.createElement('button');
-    btn.id = 'fc-add-source-btn';
+  function renderButton(probe) {
+    let btn = document.getElementById('fc-add-source-btn');
+    if (!btn) {
+      btn = document.createElement('button');
+      btn.id = 'fc-add-source-btn';
+      btn.addEventListener('click', onClick);
+      document.body.appendChild(btn);
+    }
+    // Reset state classes so re-renders (SPA navigation) don't stack.
     btn.className = 'fc-add-source-btn';
-    btn.textContent = '+ Add to FabledCurator';
-    btn.addEventListener('click', onClick);
-    document.body.appendChild(btn);
+    btn.classList.add(`fc-add-source-btn--${stateModifier(probe)}`);
+    btn.textContent = labelFor(probe);
+    btn.disabled = false;
+  }
+
+  function stateModifier(probe) {
+    if (!probe || probe.error) return 'new';
+    return ({
+      source_match: 'source-match',
+      artist_match: 'artist-match',
+      new: 'new',
+    })[probe.state] || 'new';
+  }
+
+  function labelFor(probe) {
+    if (!probe || probe.error) return '+ Add to FabledCurator';
+    const platformName = platformDisplayName(probe.platform);
+    const artistName = probe.artist?.name;
+    switch (probe.state) {
+      case 'source_match':
+        return `✓ In FabledCurator · ${platformName}`;
+      case 'artist_match':
+        return `+ Add ${platformName} source to ${artistName || 'artist'}`;
+      case 'new':
+      default:
+        return '+ Add to FabledCurator';
+    }
+  }
+
+  function platformDisplayName(key) {
+    return PLATFORMS[key]?.name || key || '';
   }
 
   async function onClick() {
     const btn = document.getElementById('fc-add-source-btn');
+    if (!btn) return;
     btn.disabled = true;
     const original = btn.textContent;
+    const probe = currentProbe;
+
+    if (probe?.state === 'source_match') {
+      btn.textContent = 'Opening…';
+      try {
+        const r = await browser.runtime.sendMessage({
+          type: 'OPEN_ARTIST_PAGE',
+          slug: probe.artist?.slug,
+        });
+        if (r?.error) showToast(`Error: ${r.error}`, 'error');
+      } catch (e) {
+        showToast(`Error: ${e.message}`, 'error');
+      } finally {
+        btn.disabled = false;
+        btn.textContent = original;
+      }
+      return;
+    }
+
     btn.textContent = 'Adding…';
     try {
       const r = await browser.runtime.sendMessage({
         type: 'ADD_AS_SOURCE',
         url: window.location.href,
       });
-      if (r.error) {
+      if (r?.error) {
         showToast(`Error: ${r.error}`, 'error');
       } else {
         const verb = r.created_source ? 'Added' : 'Already a source for';
         showToast(`${verb} ${r.artist?.name || 'artist'} (${r.source?.platform || ''})`, 'success');
+        // Re-probe so the chip flips green without waiting for the next
+        // navigation.
+        evaluate();
+        return;
       }
     } catch (e) {
       showToast(`Error: ${e.message}`, 'error');
diff --git a/extension/lib/api.js b/extension/lib/api.js
index 60fc95d..37b2c74 100644
--- a/extension/lib/api.js
+++ b/extension/lib/api.js
@@ -83,6 +83,12 @@ class FabledCuratorAPI {
   quickAddSource(url) {
     return this.request('POST', '/extension/quick-add-source', { url });
   }
+  probeSource(url) {
+    // Read-only existence check. Drives the content-script chip's
+    // color/copy BEFORE the operator clicks Add.
+    const qs = new URLSearchParams({ url }).toString();
+    return this.request('GET', `/extension/probe?${qs}`);
+  }
 
   // Connection test = the cheapest read with auth.
   testConnection() {
diff --git a/extension/manifest.json b/extension/manifest.json
index 1bc2f47..701884e 100644
--- a/extension/manifest.json
+++ b/extension/manifest.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "FabledCurator",
-  "version": "1.0.5",
+  "version": "1.0.6",
   "description": "Export cookies from supported platforms to FabledCurator and add creators as sources in one click.",
 
   "browser_specific_settings": {
diff --git a/extension/package.json b/extension/package.json
index d38e933..d6151b9 100644
--- a/extension/package.json
+++ b/extension/package.json
@@ -1,6 +1,6 @@
 {
   "name": "fabledcurator-extension",
-  "version": "1.0.5",
+  "version": "1.0.6",
   "private": true,
   "description": "Firefox extension for FabledCurator",
   "scripts": {
diff --git a/tests/test_api_extension.py b/tests/test_api_extension.py
index 9f79c0e..98c7dec 100644
--- a/tests/test_api_extension.py
+++ b/tests/test_api_extension.py
@@ -135,6 +135,114 @@ async def test_quick_add_source_wrong_key_401(client, ext_key):
     assert resp.status_code == 401
 
 
+# --- /api/extension/probe ---------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_probe_returns_new_when_nothing_exists(client, ext_key):
+    resp = await client.get(
+        "/api/extension/probe",
+        query_string={"url": "https://www.patreon.com/freshcreator"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["state"] == "new"
+    assert body["platform"] == "patreon"
+    assert body["slug"] == "freshcreator"
+
+
+@pytest.mark.asyncio
+async def test_probe_returns_source_match_for_already_added(client, ext_key, db):
+    artist = Artist(name="Alice", slug="alice", is_subscription=True)
+    db.add(artist)
+    await db.flush()
+    src = Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://www.patreon.com/alice", enabled=True, config_overrides={},
+    )
+    db.add(src)
+    await db.commit()
+
+    resp = await client.get(
+        "/api/extension/probe",
+        query_string={"url": "https://www.patreon.com/alice"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["state"] == "source_match"
+    assert body["artist"]["slug"] == "alice"
+    assert body["source"]["url"] == "https://www.patreon.com/alice"
+    assert body["source"]["platform"] == "patreon"
+
+
+@pytest.mark.asyncio
+async def test_probe_returns_artist_match_when_only_synthetic_anchor_exists(
+    client, ext_key, db,
+):
+    """Filesystem-imported artist with only a sidecar synthetic Source
+    for the (artist, platform) — the URL the operator's browsing isn't
+    yet a real Source. The probe should collapse this into artist_match
+    so the chip says '+ Add Patreon source to Dymkens' rather than
+    '+ Add to FabledCurator' (which would re-create the artist)."""
+    artist = Artist(name="Dymkens", slug="dymkens", is_subscription=False)
+    db.add(artist)
+    await db.flush()
+    synthetic = Source(
+        artist_id=artist.id, platform="patreon",
+        url="sidecar:patreon:dymkens", enabled=False, config_overrides={},
+    )
+    db.add(synthetic)
+    await db.commit()
+
+    resp = await client.get(
+        "/api/extension/probe",
+        query_string={"url": "https://www.patreon.com/dymkens"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["state"] == "artist_match"
+    assert body["artist"]["slug"] == "dymkens"
+    assert "source" not in body
+
+
+@pytest.mark.asyncio
+async def test_probe_returns_unknown_platform_for_non_artist_url(client, ext_key):
+    """A patreon URL that isn't an artist page (e.g. /home, /posts/N)
+    shouldn't trigger the button. Sentinel 'unknown_platform' state
+    tells the content script to skip injection."""
+    resp = await client.get(
+        "/api/extension/probe",
+        query_string={"url": "https://www.patreon.com/posts/12345"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["state"] == "unknown_platform"
+
+
+@pytest.mark.asyncio
+async def test_probe_missing_key_401(client):
+    resp = await client.get(
+        "/api/extension/probe",
+        query_string={"url": "https://www.patreon.com/maewix"},
+    )
+    assert resp.status_code == 401
+
+
+@pytest.mark.asyncio
+async def test_probe_missing_url_400(client, ext_key):
+    resp = await client.get(
+        "/api/extension/probe",
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 400
+    body = await resp.get_json()
+    assert body["error"] == "invalid_body"
+
+
 @pytest.mark.asyncio
 async def test_quick_add_source_missing_body_400(client, ext_key):
     resp = await client.post(