diff --git a/abogen/domain/title_builder.py b/abogen/domain/title_builder.py
new file mode 100644
index 0000000..d3e5ca5
--- /dev/null
+++ b/abogen/domain/title_builder.py
@@ -0,0 +1,97 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Dict, List, Mapping, Optional
+
+from .metadata_helpers import (
+    ensure_sentence,
+    extract_series_metadata,
+    format_author_sentence,
+    format_series_sentence,
+    normalize_metadata_map,
+)
+
+
+def build_title_intro_text(
+    metadata: Optional[Mapping[str, Any]],
+    fallback_basename: str,
+) -> str:
+    """Build the title introduction text from metadata."""
+    normalized = normalize_metadata_map(metadata)
+    fallback_title = Path(fallback_basename).stem if fallback_basename else ""
+    title = (
+        normalized.get("title")
+        or normalized.get("book_title")
+        or normalized.get("album")
+        or fallback_title
+    )
+    if not title:
+        title = fallback_title
+    subtitle = normalized.get("subtitle") or normalized.get("sub_title")
+    if subtitle and title and subtitle.casefold() == title.casefold():
+        subtitle = ""
+
+    author_value = ""
+    for candidate in ("artist", "album_artist", "author", "authors", "writer", "composer"):
+        value = normalized.get(candidate)
+        if value:
+            author_value = value
+            break
+
+    series_name, series_number = extract_series_metadata(normalized)
+    series_sentence = format_series_sentence(series_name, series_number)
+
+    sentences: List[str] = []
+    if series_sentence:
+        sentences.append(ensure_sentence(series_sentence))
+    if title:
+        sentences.append(ensure_sentence(title))
+    if subtitle:
+        sentences.append(ensure_sentence(subtitle))
+    author_sentence = format_author_sentence(author_value)
+    if author_sentence:
+        sentences.append(ensure_sentence(author_sentence))
+    return " ".join(sentences).strip()
+
+
+def build_outro_text(
+    metadata: Optional[Mapping[str, Any]],
+    fallback_basename: str,
+) -> str:
+    """Build the outro/closing text from metadata."""
+    normalized = normalize_metadata_map(metadata)
+    fallback_title = Path(fallback_basename).stem if fallback_basename else ""
+    title = (
+        normalized.get("title")
+        or normalized.get("book_title")
+        or normalized.get("album")
+        or fallback_title
+    )
+    author_value = ""
+    for candidate in ("authors", "author", "album_artist", "artist", "writer", "composer"):
+        value = normalized.get(candidate)
+        if value:
+            author_value = value
+            break
+    author_sentence = format_author_sentence(author_value)
+    authors_fragment = (
+        author_sentence[3:].strip() if author_sentence.lower().startswith("by ") else author_sentence.strip()
+    )
+
+    if title and authors_fragment:
+        closing_line = f"The end of {title} from {authors_fragment}"
+    elif title:
+        closing_line = f"The end of {title}"
+    elif authors_fragment:
+        closing_line = f"The end from {authors_fragment}"
+    else:
+        closing_line = "The end"
+
+    series_name, series_number = extract_series_metadata(normalized)
+    series_sentence = format_series_sentence(series_name, series_number)
+
+    sentences: List[str] = [ensure_sentence(closing_line)]
+    if series_sentence:
+        sentences.append(ensure_sentence(series_sentence))
+
+    return " ".join(sentence for sentence in sentences if sentence).strip()
\ No newline at end of file
diff --git a/abogen/webui/conversion_runner.py b/abogen/webui/conversion_runner.py
index 35e41b2..3a345b3 100644
--- a/abogen/webui/conversion_runner.py
+++ b/abogen/webui/conversion_runner.py
@@ -62,6 +62,10 @@ from abogen.domain.metadata_helpers import (
     extract_series_metadata as _extract_series_metadata,
     format_series_sentence as _format_series_sentence,
 )
+from abogen.domain.title_builder import (
+    build_title_intro_text as _build_title_intro_text,
+    build_outro_text as _build_outro_text,
+)
 
 
 from .service import Job, JobStatus
@@ -167,81 +171,6 @@ def _coerce_truthy(value: Any, default: bool = True) -> bool:
 _OUTPUT_SANITIZE_RE = re.compile(r"[^\w\-_.]+")
 
 
-def _build_title_intro_text(
-    metadata: Optional[Mapping[str, Any]],
-    fallback_basename: str,
-) -> str:
-    normalized = _normalize_metadata_map(metadata)
-    fallback_title = Path(fallback_basename).stem if fallback_basename else ""
-    title = normalized.get("title") or normalized.get("book_title") or normalized.get("album") or fallback_title
-    if not title:
-        title = fallback_title
-    subtitle = normalized.get("subtitle") or normalized.get("sub_title")
-    if subtitle and title and subtitle.casefold() == title.casefold():
-        subtitle = ""
-    author_value = ""
-    for candidate in ("artist", "album_artist", "author", "authors", "writer", "composer"):
-        value = normalized.get(candidate)
-        if value:
-            author_value = value
-            break
-
-    series_name, series_number = _extract_series_metadata(normalized)
-    series_sentence = _format_series_sentence(series_name, series_number)
-
-    sentences: List[str] = []
-    if series_sentence:
-        sentences.append(_ensure_sentence(series_sentence))
-    if title:
-        sentences.append(_ensure_sentence(title))
-    if subtitle:
-        sentences.append(_ensure_sentence(subtitle))
-    author_sentence = _format_author_sentence(author_value)
-    if author_sentence:
-        sentences.append(_ensure_sentence(author_sentence))
-    return " ".join(sentences).strip()
-
-
-def _build_outro_text(
-    metadata: Optional[Mapping[str, Any]],
-    fallback_basename: str,
-) -> str:
-    normalized = _normalize_metadata_map(metadata)
-    fallback_title = Path(fallback_basename).stem if fallback_basename else ""
-    title = (
-        normalized.get("title")
-        or normalized.get("book_title")
-        or normalized.get("album")
-        or fallback_title
-    )
-    author_value = ""
-    for candidate in ("authors", "author", "album_artist", "artist", "writer", "composer"):
-        value = normalized.get(candidate)
-        if value:
-            author_value = value
-            break
-    author_sentence = _format_author_sentence(author_value)
-    authors_fragment = author_sentence[3:].strip() if author_sentence.lower().startswith("by ") else author_sentence.strip()
-
-    if title and authors_fragment:
-        closing_line = f"The end of {title} from {authors_fragment}"
-    elif title:
-        closing_line = f"The end of {title}"
-    elif authors_fragment:
-        closing_line = f"The end from {authors_fragment}"
-    else:
-        closing_line = "The end"
-
-    series_name, series_number = _extract_series_metadata(normalized)
-    series_sentence = _format_series_sentence(series_name, series_number)
-
-    sentences: List[str] = [_ensure_sentence(closing_line)]
-    if series_sentence:
-        sentences.append(_ensure_sentence(series_sentence))
-
-    return " ".join(sentence for sentence in sentences if sentence).strip()
-
-
 def _spec_to_voice_ids(spec: Any) -> Set[str]:
     text = str(spec or "").strip()
     if not text:
diff --git a/tests/test_title_builder.py b/tests/test_title_builder.py
new file mode 100644
index 0000000..af6dcd0
--- /dev/null
+++ b/tests/test_title_builder.py
@@ -0,0 +1,59 @@
+"""Tests for domain/title_builder.py."""
+import sys
+import os
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), "..")))
+
+from abogen.domain.title_builder import build_title_intro_text, build_outro_text
+
+
+class TestBuildTitleIntroText:
+    def test_empty_metadata(self):
+        result = build_title_intro_text({}, "book.epub")
+        assert result == "book."
+
+    def test_title_from_metadata(self):
+        result = build_title_intro_text({"title": "My Book"}, "book.epub")
+        assert result == "My Book."
+
+    def test_title_fallback_basename(self):
+        result = build_title_intro_text({}, "my_book.epub")
+        assert result == "my_book."
+
+    def test_with_author(self):
+        result = build_title_intro_text({"title": "My Book", "author": "John Doe"}, "book.epub")
+        assert result == "My Book. By John Doe."
+
+    def test_with_subtitle(self):
+        result = build_title_intro_text({"title": "My Book", "subtitle": "A Tale"}, "book.epub")
+        assert result == "My Book. A Tale."
+
+    def test_duplicate_title_subtitle(self):
+        result = build_title_intro_text({"title": "My Book", "subtitle": "My Book"}, "book.epub")
+        assert result == "My Book."
+
+    def test_with_series(self):
+        result = build_title_intro_text({"title": "My Book", "series": "Series", "series_index": "3"}, "book.epub")
+        assert result == "Book 3 of the Series. My Book."
+
+
+class TestBuildOutroText:
+    def test_empty(self):
+        result = build_outro_text({}, "book.epub")
+        assert result == "The end of book."
+
+    def test_title_only(self):
+        result = build_outro_text({"title": "My Book"}, "book.epub")
+        assert result == "The end of My Book."
+
+    def test_author_only(self):
+        result = build_outro_text({"author": "John Doe"}, "book.epub")
+        assert result == "The end of book from John Doe."
+
+    def test_title_and_author(self):
+        result = build_outro_text({"title": "My Book", "author": "John Doe"}, "book.epub")
+        assert result == "The end of My Book from John Doe."
+
+    def test_with_series(self):
+        result = build_outro_text({"title": "My Book", "series": "Series", "series_index": "3"}, "book.epub")
+        assert "The end of My Book." in result
+        assert "Book 3 of the Series." in result
\ No newline at end of file