diff --git a/README.md b/README.md
index ea49014..79b05c2 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,7 @@
 - Split view with post body / repo stats and threaded comments or README side by side
 - Filter feed by source, refresh on demand, paginate with `m`
 - Keyword search with `/`, copy URL with `y`, mark seen posts dimmed automatically
-- Config file at `~/.devskim/config.toml` — created automatically on first run
+- Config file at `${XDG_CONFIG_HOME:-~/.config}/devskim/config.toml` — created automatically on first run
 
 ## Install
 
@@ -57,10 +57,10 @@ pip install -e .
 
 ---
 
-On first run, a config file is created at `~/.devskim/config.toml`. Edit it to change subreddits:
+On first run, a config file is created at `$XDG_CONFIG_HOME/devskim/config.toml` (defaults to `~/.config/devskim/config.toml`). Edit it to change subreddits:
 
 ```bash
-nano ~/.devskim/config.toml
+nano "${XDG_CONFIG_HOME:-~/.config}/devskim/config.toml"
 ```
 
 ```toml
@@ -108,7 +108,7 @@ Run `devskim` — changes take effect on next launch or press `r` to refresh.
 
 ## Config
 
-`~/.devskim/config.toml` — created on first run with defaults.
+`$XDG_CONFIG_HOME/devskim/config.toml` (default: `~/.config/devskim/config.toml`) — created on first run with defaults. If `~/.devskim` exists and the XDG path does not, the legacy location is used automatically.
 
 | Key | Default | Description |
 |-----|---------|-------------|
diff --git a/devskim/config.py b/devskim/config.py
index cb92c50..32ba09a 100644
--- a/devskim/config.py
+++ b/devskim/config.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import json
+import os
 import time
 
 try:
@@ -10,9 +11,38 @@
 from dataclasses import dataclass, field
 from pathlib import Path
 
-CONFIG_DIR = Path.home() / ".devskim"
+
+def _resolve_config_dir() -> Path:
+    xdg = os.environ.get("XDG_CONFIG_HOME")
+    if xdg and Path(xdg).is_absolute():
+        return Path(xdg) / "devskim"
+    xdg_default = Path.home() / ".config" / "devskim"
+    legacy = Path.home() / ".devskim"
+    # Keep existing installs working if they have ~/.devskim and no XDG dir yet.
+    if legacy.is_dir() and not xdg_default.exists():
+        return legacy
+    return xdg_default
+
+
+def _resolve_cache_dir() -> Path:
+    xdg = os.environ.get("XDG_CACHE_HOME")
+    if xdg and Path(xdg).is_absolute():
+        return Path(xdg) / "devskim"
+    return Path.home() / ".cache" / "devskim"
+
+
+def _resolve_data_dir() -> Path:
+    xdg = os.environ.get("XDG_DATA_HOME")
+    if xdg and Path(xdg).is_absolute():
+        return Path(xdg) / "devskim"
+    return Path.home() / ".local" / "share" / "devskim"
+
+
+CONFIG_DIR = _resolve_config_dir()
 CONFIG_PATH = CONFIG_DIR / "config.toml"
-CACHE_PATH = CONFIG_DIR / "cache.json"
+CACHE_DIR = _resolve_cache_dir()
+CACHE_PATH = CACHE_DIR / "cache.json"
+DATA_DIR = _resolve_data_dir()
 
 DEFAULT_CONFIG = """\
 subreddits = ["programming", "ClaudeAI", "machinelearning"]
@@ -28,7 +58,7 @@
 
 @dataclass
 class Config:
-    """Runtime settings loaded from ~/.devskim/config.toml."""
+    """Runtime settings loaded from $XDG_CONFIG_HOME/devskim/config.toml."""
 
     subreddits: list[str] = field(
         default_factory=lambda: ["programming", "python", "machinelearning"]
@@ -79,7 +109,7 @@ def load_cache(ttl_minutes: int) -> list[dict] | None:
 def save_cache(items: list[dict]) -> None:
     """Write feed items to disk with a current timestamp."""
     try:
-        CONFIG_DIR.mkdir(parents=True, exist_ok=True)
+        CACHE_DIR.mkdir(parents=True, exist_ok=True)
         CACHE_PATH.write_text(json.dumps({"ts": time.time(), "items": items}))
     except Exception:
         pass
diff --git a/devskim/seen.py b/devskim/seen.py
index 6e2a129..1cdd41b 100644
--- a/devskim/seen.py
+++ b/devskim/seen.py
@@ -3,9 +3,9 @@
 import json
 import time
 
-from .config import CONFIG_DIR
+from .config import DATA_DIR
 
-SEEN_PATH = CONFIG_DIR / "seen.json"
+SEEN_PATH = DATA_DIR / "seen.json"
 SEEN_TTL_SECONDS = 86_400  # 1 day
 
 
@@ -44,7 +44,7 @@ def load_seen() -> set[str]:
 def mark_seen(post_id: str) -> bool:
     """Record post_id as seen, pruning entries older than the TTL. Returns False on write failure."""
     try:
-        CONFIG_DIR.mkdir(parents=True, exist_ok=True)
+        DATA_DIR.mkdir(parents=True, exist_ok=True)
         cutoff = time.time() - SEEN_TTL_SECONDS
         data = {pid: ts for pid, ts in _load_raw().items() if ts >= cutoff}
         data[post_id] = time.time()
diff --git a/tests/test_config.py b/tests/test_config.py
index 9b9bdc4..2b93e26 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1,8 +1,61 @@
 import json
+import os
 import time
 from unittest.mock import patch
 
-from devskim.config import Config, load_cache, load_config, save_cache
+from devskim.config import (
+    Config,
+    _resolve_cache_dir,
+    _resolve_config_dir,
+    _resolve_data_dir,
+    load_cache,
+    load_config,
+    save_cache,
+)
+
+
+def test_resolve_config_dir_xdg_env(tmp_path):
+    with patch.dict(os.environ, {"XDG_CONFIG_HOME": str(tmp_path)}, clear=False):
+        result = _resolve_config_dir()
+    assert result == tmp_path / "devskim"
+
+
+def test_resolve_config_dir_xdg_relative_ignored():
+    with patch.dict(os.environ, {"XDG_CONFIG_HOME": "relative/path"}, clear=False):
+        result = _resolve_config_dir()
+    assert result.is_absolute()
+
+
+def test_resolve_config_dir_xdg_default(tmp_path):
+    env = {k: v for k, v in os.environ.items() if k != "XDG_CONFIG_HOME"}
+    with patch.dict(os.environ, env, clear=True):
+        with patch("devskim.config.Path") as mock_path:
+            mock_home = tmp_path
+            mock_path.home.return_value = mock_home
+            result = _resolve_config_dir()
+    assert result == mock_home / ".config" / "devskim"
+
+
+def test_resolve_config_dir_legacy_fallback(tmp_path):
+    legacy = tmp_path / ".devskim"
+    legacy.mkdir()
+    env = {k: v for k, v in os.environ.items() if k != "XDG_CONFIG_HOME"}
+    with patch.dict(os.environ, env, clear=True):
+        with patch("devskim.config.Path") as mock_path:
+            mock_path.home.return_value = tmp_path
+            result = _resolve_config_dir()
+    assert result == legacy
+
+
+def test_resolve_config_dir_xdg_takes_priority_over_legacy(tmp_path):
+    legacy = tmp_path / ".devskim"
+    legacy.mkdir()
+    xdg_dir = tmp_path / "xdg"
+    xdg_dir.mkdir()
+    (xdg_dir / "devskim").mkdir()
+    with patch.dict(os.environ, {"XDG_CONFIG_HOME": str(xdg_dir)}, clear=False):
+        result = _resolve_config_dir()
+    assert result == xdg_dir / "devskim"
 
 
 def test_config_defaults():
@@ -69,7 +122,7 @@ def test_save_and_reload_cache(tmp_path):
     items = [{"title": "test", "source": "HN"}]
     with (
         patch("devskim.config.CACHE_PATH", cache_path),
-        patch("devskim.config.CONFIG_DIR", tmp_path),
+        patch("devskim.config.CACHE_DIR", tmp_path),
     ):
         save_cache(items)
         result = load_cache(10)
@@ -81,8 +134,50 @@ def test_save_cache_writes_timestamp(tmp_path):
     before = time.time()
     with (
         patch("devskim.config.CACHE_PATH", cache_path),
-        patch("devskim.config.CONFIG_DIR", tmp_path),
+        patch("devskim.config.CACHE_DIR", tmp_path),
     ):
         save_cache([])
     data = json.loads(cache_path.read_text())
     assert abs(data["ts"] - before) < 5
+
+
+def test_resolve_cache_dir_xdg_env(tmp_path):
+    with patch.dict(os.environ, {"XDG_CACHE_HOME": str(tmp_path)}, clear=False):
+        result = _resolve_cache_dir()
+    assert result == tmp_path / "devskim"
+
+
+def test_resolve_cache_dir_xdg_relative_ignored():
+    with patch.dict(os.environ, {"XDG_CACHE_HOME": "relative/cache"}, clear=False):
+        result = _resolve_cache_dir()
+    assert result.is_absolute()
+
+
+def test_resolve_cache_dir_default(tmp_path):
+    env = {k: v for k, v in os.environ.items() if k != "XDG_CACHE_HOME"}
+    with patch.dict(os.environ, env, clear=True):
+        with patch("devskim.config.Path") as mock_path:
+            mock_path.home.return_value = tmp_path
+            result = _resolve_cache_dir()
+    assert result == tmp_path / ".cache" / "devskim"
+
+
+def test_resolve_data_dir_xdg_env(tmp_path):
+    with patch.dict(os.environ, {"XDG_DATA_HOME": str(tmp_path)}, clear=False):
+        result = _resolve_data_dir()
+    assert result == tmp_path / "devskim"
+
+
+def test_resolve_data_dir_xdg_relative_ignored():
+    with patch.dict(os.environ, {"XDG_DATA_HOME": "relative/data"}, clear=False):
+        result = _resolve_data_dir()
+    assert result.is_absolute()
+
+
+def test_resolve_data_dir_default(tmp_path):
+    env = {k: v for k, v in os.environ.items() if k != "XDG_DATA_HOME"}
+    with patch.dict(os.environ, env, clear=True):
+        with patch("devskim.config.Path") as mock_path:
+            mock_path.home.return_value = tmp_path
+            result = _resolve_data_dir()
+    assert result == tmp_path / ".local" / "share" / "devskim"
diff --git a/tests/test_seen.py b/tests/test_seen.py
index 1e3b4cb..96733ec 100644
--- a/tests/test_seen.py
+++ b/tests/test_seen.py
@@ -114,7 +114,7 @@ def test_load_seen_empty_file(monkeypatch, tmp_path):
 def test_mark_seen_creates_file(monkeypatch, tmp_path):
     seen_path = tmp_path / "seen.json"
     monkeypatch.setattr(seen_module, "SEEN_PATH", seen_path)
-    monkeypatch.setattr(seen_module, "CONFIG_DIR", tmp_path)
+    monkeypatch.setattr(seen_module, "DATA_DIR", tmp_path)
     assert mark_seen("HN:42") is True
     assert seen_path.exists()
 
@@ -122,7 +122,7 @@ def test_mark_seen_creates_file(monkeypatch, tmp_path):
 def test_mark_seen_persists_id(monkeypatch, tmp_path):
     seen_path = tmp_path / "seen.json"
     monkeypatch.setattr(seen_module, "SEEN_PATH", seen_path)
-    monkeypatch.setattr(seen_module, "CONFIG_DIR", tmp_path)
+    monkeypatch.setattr(seen_module, "DATA_DIR", tmp_path)
     mark_seen("HN:99")
     data = json.loads(seen_path.read_text())
     assert "HN:99" in data
@@ -133,7 +133,7 @@ def test_mark_seen_prunes_expired(monkeypatch, tmp_path):
     old_ts = time.time() - 90_000
     seen_path.write_text(json.dumps({"HN:old": old_ts}))
     monkeypatch.setattr(seen_module, "SEEN_PATH", seen_path)
-    monkeypatch.setattr(seen_module, "CONFIG_DIR", tmp_path)
+    monkeypatch.setattr(seen_module, "DATA_DIR", tmp_path)
     mark_seen("HN:new")
     data = json.loads(seen_path.read_text())
     assert "HN:old" not in data
@@ -145,7 +145,7 @@ def test_mark_seen_overwrites_existing_id(monkeypatch, tmp_path):
     old_ts = time.time() - 100
     seen_path.write_text(json.dumps({"HN:1": old_ts}))
     monkeypatch.setattr(seen_module, "SEEN_PATH", seen_path)
-    monkeypatch.setattr(seen_module, "CONFIG_DIR", tmp_path)
+    monkeypatch.setattr(seen_module, "DATA_DIR", tmp_path)
     mark_seen("HN:1")
     data = json.loads(seen_path.read_text())
     assert data["HN:1"] > old_ts
@@ -154,5 +154,5 @@ def test_mark_seen_overwrites_existing_id(monkeypatch, tmp_path):
 def test_mark_seen_returns_false_on_write_failure(monkeypatch, tmp_path):
     # SEEN_PATH points to an existing directory — write_text will fail
     monkeypatch.setattr(seen_module, "SEEN_PATH", tmp_path)
-    monkeypatch.setattr(seen_module, "CONFIG_DIR", tmp_path)
+    monkeypatch.setattr(seen_module, "DATA_DIR", tmp_path)
     assert mark_seen("HN:42") is False