diff --git a/app/platforms/ebay/categories.py b/app/platforms/ebay/categories.py
new file mode 100644
index 0000000..d02896d
--- /dev/null
+++ b/app/platforms/ebay/categories.py
@@ -0,0 +1,78 @@
+# app/platforms/ebay/categories.py
+# MIT License
+"""eBay category cache — fetches leaf categories from the Taxonomy API and stores them
+in the local SQLite DB for injection into LLM query-builder prompts.
+
+Refreshed weekly. Falls back to a hardcoded bootstrap table when no eBay API
+credentials are configured (scraper-only users still get usable category hints).
+"""
+from __future__ import annotations
+
+import logging
+import sqlite3
+from datetime import datetime, timedelta, timezone
+from typing import Optional
+
+log = logging.getLogger(__name__)
+
+# Bootstrap table — common categories for self-hosters without eBay API credentials.
+# category_id values are stable eBay leaf IDs (US marketplace, as of 2026).
+_BOOTSTRAP_CATEGORIES: list[tuple[str, str, str]] = [
+    ("27386", "Graphics Cards",     "Consumer Electronics > Computers > Components > Graphics/Video Cards"),
+    ("164",   "CPUs/Processors",    "Consumer Electronics > Computers > Components > CPUs/Processors"),
+    ("170083","RAM",                "Consumer Electronics > Computers > Components > Memory (RAM)"),
+    ("175669","Solid State Drives", "Consumer Electronics > Computers > Components > Drives > Solid State Drives"),
+    ("177089","Hard Drives",        "Consumer Electronics > Computers > Components > Drives > Hard Drives"),
+    ("179142","Laptops",            "Consumer Electronics > Computers > Laptops & Netbooks"),
+    ("171957","Desktop Computers",  "Consumer Electronics > Computers > Desktops & All-in-Ones"),
+    ("293",   "Consumer Electronics","Consumer Electronics"),
+    ("625",   "Cameras",            "Consumer Electronics > Cameras & Photography > Digital Cameras"),
+    ("15052", "Vintage Cameras",    "Consumer Electronics > Cameras & Photography > Vintage Movie Cameras"),
+    ("11724", "Audio Equipment",    "Consumer Electronics > TV, Video & Home Audio > Home Audio"),
+    ("3676",  "Vinyl Records",      "Music > Records"),
+    ("870",   "Musical Instruments","Musical Instruments & Gear"),
+    ("31388", "Video Game Consoles","Video Games & Consoles > Video Game Consoles"),
+    ("139971","Video Games",        "Video Games & Consoles > Video Games"),
+    ("139973","Video Game Accessories", "Video Games & Consoles > Video Game Accessories"),
+    ("14308", "Networking Gear",    "Computers/Tablets & Networking > Home Networking & Connectivity"),
+    ("182062","Smartphones",        "Cell Phones & Smartphones"),
+    ("9394",  "Tablets",            "Computers/Tablets & Networking > Tablets & eBook Readers"),
+    ("11233", "Collectibles",       "Collectibles"),
+]
+
+
+class EbayCategoryCache:
+    """Caches eBay leaf categories in SQLite for LLM prompt injection.
+
+    Args:
+        conn: An open sqlite3.Connection with migration 011 already applied.
+    """
+
+    def __init__(self, conn: sqlite3.Connection) -> None:
+        self._conn = conn
+
+    def is_stale(self, max_age_days: int = 7) -> bool:
+        """Return True if the cache is empty or all entries are older than max_age_days."""
+        cur = self._conn.execute("SELECT MAX(refreshed_at) FROM ebay_categories")
+        row = cur.fetchone()
+        if not row or not row[0]:
+            return True
+        try:
+            latest = datetime.fromisoformat(row[0])
+            if latest.tzinfo is None:
+                latest = latest.replace(tzinfo=timezone.utc)
+            return datetime.now(timezone.utc) - latest > timedelta(days=max_age_days)
+        except ValueError:
+            return True
+
+    def _seed_bootstrap(self) -> None:
+        """Insert the hardcoded bootstrap categories. Idempotent (ON CONFLICT IGNORE)."""
+        now = datetime.now(timezone.utc).isoformat()
+        self._conn.executemany(
+            "INSERT OR IGNORE INTO ebay_categories"
+            " (category_id, name, full_path, is_leaf, refreshed_at)"
+            " VALUES (?, ?, ?, 1, ?)",
+            [(cid, name, path, now) for cid, name, path in _BOOTSTRAP_CATEGORIES],
+        )
+        self._conn.commit()
+        log.info("EbayCategoryCache: seeded %d bootstrap categories.", len(_BOOTSTRAP_CATEGORIES))
diff --git a/tests/test_ebay_categories.py b/tests/test_ebay_categories.py
new file mode 100644
index 0000000..de791e4
--- /dev/null
+++ b/tests/test_ebay_categories.py
@@ -0,0 +1,58 @@
+"""Unit tests for EbayCategoryCache."""
+from __future__ import annotations
+
+import sqlite3
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+import pytest
+
+from app.platforms.ebay.categories import EbayCategoryCache
+
+BOOTSTRAP_MIN = 10  # bootstrap must seed at least this many rows
+
+
+@pytest.fixture
+def db(tmp_path):
+    """In-memory SQLite with migrations applied."""
+    from circuitforge_core.db import get_connection, run_migrations
+    conn = get_connection(tmp_path / "test.db")
+    run_migrations(conn, Path("app/db/migrations"))
+    return conn
+
+
+def test_is_stale_empty_db(db):
+    cache = EbayCategoryCache(db)
+    assert cache.is_stale() is True
+
+
+def test_is_stale_fresh(db):
+    now = datetime.now(timezone.utc).isoformat()
+    db.execute(
+        "INSERT INTO ebay_categories (category_id, name, full_path, is_leaf, refreshed_at)"
+        " VALUES (?, ?, ?, 1, ?)",
+        ("12345", "Graphics Cards", "Consumer Electronics > GPUs > Graphics Cards", now),
+    )
+    db.commit()
+    cache = EbayCategoryCache(db)
+    assert cache.is_stale() is False
+
+
+def test_is_stale_old(db):
+    old = (datetime.now(timezone.utc) - timedelta(days=8)).isoformat()
+    db.execute(
+        "INSERT INTO ebay_categories (category_id, name, full_path, is_leaf, refreshed_at)"
+        " VALUES (?, ?, ?, 1, ?)",
+        ("12345", "Graphics Cards", "Consumer Electronics > GPUs > Graphics Cards", old),
+    )
+    db.commit()
+    cache = EbayCategoryCache(db)
+    assert cache.is_stale() is True
+
+
+def test_seed_bootstrap_populates_rows(db):
+    cache = EbayCategoryCache(db)
+    cache._seed_bootstrap()
+    cur = db.execute("SELECT COUNT(*) FROM ebay_categories")
+    count = cur.fetchone()[0]
+    assert count >= BOOTSTRAP_MIN