diff --git a/ocr-service/test_spell_check.py b/ocr-service/test_spell_check.py
new file mode 100644
index 00000000..1e19bac0
--- /dev/null
+++ b/ocr-service/test_spell_check.py
@@ -0,0 +1,89 @@
+"""Tests for OCR spell-check post-processing."""
+
+import pytest
+from spell_check import correct_text, load_spell_checker
+
+
+@pytest.fixture(autouse=True)
+def ensure_loaded():
+    load_spell_checker()
+
+
+def test_known_german_word_passes_through():
+    assert correct_text("Haus") == "Haus"
+
+
+def test_obvious_gibberish_replaced_with_marker():
+    assert correct_text("xqzwrpvmk") == "[unleserlich]"
+
+
+def test_short_word_exempt_from_check():
+    assert correct_text("im") == "im"
+    assert correct_text("der") == "der"
+    assert correct_text("zu") == "zu"
+
+
+def test_unleserlich_marker_preserved():
+    assert correct_text("[unleserlich]") == "[unleserlich]"
+
+
+def test_mixed_text_correct_and_gibberish():
+    result = correct_text("Haus xqzwrpvmk Garten")
+    assert result == "Haus [unleserlich] Garten"
+
+
+def test_adjacent_gibberish_words_collapsed_to_one_marker():
+    result = correct_text("[unleserlich] xqzwrpvmk Haus")
+    assert result == "[unleserlich] Haus"
+
+
+def test_empty_string_returns_empty():
+    assert correct_text("") == ""
+
+
+def test_whitespace_only_returns_unchanged():
+    assert correct_text("   ") == "   "
+
+
+def test_existing_marker_not_doubled():
+    result = correct_text("[unleserlich] Haus [unleserlich]")
+    assert result == "[unleserlich] Haus [unleserlich]"
+
+
+def test_historical_word_passes_through():
+    assert correct_text("Thür") == "Thür"
+
+
+def test_correctable_ocr_error_gets_corrected():
+    result = correct_text("Hauus")
+    assert result == "Haus[?]"
+
+
+def test_sentence_with_multiple_corrections():
+    result = correct_text("Thür Hauus xqzwrpvmk Garten")
+    assert result == "Thür Haus[?] [unleserlich] Garten"
+
+
+def test_capitalization_preserved_on_correction():
+    # "Freunnd" (doubled n) — OCR duplication error for "Freund"
+    result = correct_text("Freunnd")
+    assert result != "Freunnd"
+    assert result != "[unleserlich]"
+    assert result[0].isupper()
+
+
+def test_raises_runtime_error_when_not_loaded(monkeypatch):
+    import spell_check as sc
+    monkeypatch.setattr(sc, "_spell", None)
+    with pytest.raises(RuntimeError, match="not loaded"):
+        correct_text("test")
+
+
+def test_punctuation_attached_token_passes_through():
+    assert correct_text("Haus,") == "Haus,"
+    assert correct_text("Garten.") == "Garten."
+
+
+def test_numeric_token_passes_through():
+    assert correct_text("1870er") == "1870er"
+    assert correct_text("18.") == "18."