diff --git a/.claude/scheduled_tasks.lock b/.claude/scheduled_tasks.lock
new file mode 100644
index 0000000..b46d20c
--- /dev/null
+++ b/.claude/scheduled_tasks.lock
@@ -0,0 +1 @@
+{"sessionId":"75cf1462-99b4-4a81-b53f-b4e42ed0a32d","pid":71635,"acquiredAt":1777021697658}
\ No newline at end of file
diff --git a/app/api.py b/app/api.py
index 6975a5b..501b908 100644
--- a/app/api.py
+++ b/app/api.py
@@ -15,9 +15,12 @@
 from starlette.requests import Request
 from sqlmodel import Session, SQLModel, col, func, or_, select
 
+import anthropic as anthropic_lib
+
 from app.auth import create_access_token, require_admin, verify_admin_password
 from app.db import get_session
 from app.feed import months_to_collapse
+from app.tag_suggester import suggest_tags
 from app.images import (
     ImageCommitError,
     ImageGenerationError,
@@ -417,6 +420,34 @@ def clear_theme_image(
     return theme
 
 
+# ---------- tag suggestion endpoint ----------
+
+
+class SuggestTagsResponse(SQLModel, table=False):
+    tags: List[str]
+
+
+@router.post("/themes/{theme_id}/suggest-tags", response_model=SuggestTagsResponse)
+def suggest_theme_tags(
+    theme_id: int,
+    session: Session = Depends(get_session),
+    _admin: None = Depends(require_admin),
+):
+    theme = session.get(Theme, theme_id)
+    if not theme:
+        raise HTTPException(status_code=404, detail="Theme not found")
+
+    existing_tag_names = [t.name for t in session.exec(select(Tag)).all()]
+
+    try:
+        tags = suggest_tags(theme.body_md, existing_tag_names)
+    except anthropic_lib.APIError as e:
+        logger.warning("Tag suggestion failed for theme %d: %s", theme_id, e)
+        raise HTTPException(status_code=503, detail="Tag suggestion service unavailable")
+
+    return SuggestTagsResponse(tags=tags)
+
+
 # ---------- breadcrumb endpoints ----------
 
 
diff --git a/app/tag_suggester.py b/app/tag_suggester.py
new file mode 100644
index 0000000..009860f
--- /dev/null
+++ b/app/tag_suggester.py
@@ -0,0 +1,56 @@
+"""Claude-powered tag suggestions for themes."""
+
+import json
+import logging
+import os
+import re
+
+import anthropic
+
+logger = logging.getLogger(__name__)
+
+_SYSTEM_PROMPT = """\
+You suggest concise, reusable tags for blog themes.
+
+Rules:
+- Return 3–5 tags as a JSON object: {"tags": ["tag-one", "tag-two"]}
+- Prefer existing tags when they fit; only invent new ones when needed
+- Tags should be lowercase words or short phrases (e.g. "deep-work", "identity")
+- Return ONLY the JSON object — no explanation, no markdown
+"""
+
+
+def suggest_tags(theme_body: str, existing_tag_names: list[str]) -> list[str]:
+    """Call Claude Haiku to suggest tags for a theme, normalized to slug format."""
+    api_key = os.getenv("ANTHROPIC_API_KEY")
+    client = anthropic.Anthropic(api_key=api_key)
+
+    existing_context = (
+        f"\n\nExisting tags on this blog (prefer these when relevant): {', '.join(existing_tag_names)}"
+        if existing_tag_names
+        else ""
+    )
+
+    response = client.messages.create(
+        model="claude-haiku-4-5-20251001",
+        max_tokens=150,
+        system=_SYSTEM_PROMPT,
+        messages=[
+            {
+                "role": "user",
+                "content": f"Theme content:\n\n{theme_body}{existing_context}",
+            }
+        ],
+    )
+
+    raw_text = response.content[0].text
+    data = json.loads(raw_text)
+    raw_tags = data.get("tags", [])
+    return [_normalize(t) for t in raw_tags if t]
+
+
+def _normalize(name: str) -> str:
+    v = re.sub(r"\s+", "-", name.strip().lower())
+    v = re.sub(r"[^a-z0-9\-]", "", v)
+    v = re.sub(r"-{2,}", "-", v)
+    return v.strip("-")
diff --git a/tests/test_api_suggest_tags.py b/tests/test_api_suggest_tags.py
new file mode 100644
index 0000000..ecb93be
--- /dev/null
+++ b/tests/test_api_suggest_tags.py
@@ -0,0 +1,90 @@
+"""Tests for POST /api/themes/{theme_id}/suggest-tags."""
+
+import json
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from app.models import Tag, Theme, Visibility
+
+
+def _make_claude_response(tags: list[str]) -> MagicMock:
+    content_block = MagicMock()
+    content_block.text = json.dumps({"tags": tags})
+    msg = MagicMock()
+    msg.content = [content_block]
+    return msg
+
+
+@pytest.fixture
+def theme(session):
+    t = Theme(body_md="Reflections on solitude and the nature of attention", visibility=Visibility.draft)
+    session.add(t)
+    session.commit()
+    session.refresh(t)
+    return t
+
+
+@pytest.fixture
+def theme_with_tags(session, theme):
+    for name in ["mindfulness", "philosophy"]:
+        tag = Tag(name=name)
+        session.add(tag)
+        theme.tags.append(tag)
+    session.add(theme)
+    session.commit()
+    session.refresh(theme)
+    return theme
+
+
+def test_suggest_tags_returns_normalized_tags(client, theme):
+    mock_response = _make_claude_response(["solitude", "attention", "reflection"])
+    with patch("app.tag_suggester.anthropic.Anthropic") as mock_cls:
+        mock_cls.return_value.messages.create.return_value = mock_response
+        response = client.post(f"/api/themes/{theme.id}/suggest-tags")
+
+    assert response.status_code == 200
+    data = response.json()
+    assert "tags" in data
+    assert data["tags"] == ["solitude", "attention", "reflection"]
+
+
+def test_suggest_tags_passes_existing_tags_for_context(client, theme_with_tags):
+    mock_response = _make_claude_response(["mindfulness", "focus"])
+    with patch("app.tag_suggester.anthropic.Anthropic") as mock_cls:
+        mock_instance = mock_cls.return_value
+        mock_instance.messages.create.return_value = mock_response
+        client.post(f"/api/themes/{theme_with_tags.id}/suggest-tags")
+
+    call_kwargs = mock_instance.messages.create.call_args
+    prompt_text = call_kwargs.kwargs["messages"][0]["content"]
+    assert "mindfulness" in prompt_text
+    assert "philosophy" in prompt_text
+
+
+def test_suggest_tags_normalizes_raw_output(client, theme):
+    mock_response = _make_claude_response(["Deep Work", "mind fullness", "self--care"])
+    with patch("app.tag_suggester.anthropic.Anthropic") as mock_cls:
+        mock_cls.return_value.messages.create.return_value = mock_response
+        response = client.post(f"/api/themes/{theme.id}/suggest-tags")
+
+    assert response.status_code == 200
+    assert response.json()["tags"] == ["deep-work", "mind-fullness", "self-care"]
+
+
+def test_suggest_tags_returns_404_for_missing_theme(client):
+    with patch("app.tag_suggester.anthropic.Anthropic"):
+        response = client.post("/api/themes/999/suggest-tags")
+    assert response.status_code == 404
+
+
+def test_suggest_tags_returns_503_on_api_error(client, theme):
+    import anthropic as anthropic_lib
+
+    with patch("app.tag_suggester.anthropic.Anthropic") as mock_cls:
+        mock_cls.return_value.messages.create.side_effect = anthropic_lib.APIError(
+            message="rate limited", request=MagicMock(), body=None
+        )
+        response = client.post(f"/api/themes/{theme.id}/suggest-tags")
+
+    assert response.status_code == 503