diff --git a/src/polydiff/cli.py b/src/polydiff/cli.py
index 5b9fc44..f7ff03d 100644
--- a/src/polydiff/cli.py
+++ b/src/polydiff/cli.py
@@ -13,8 +13,6 @@
 from .core.git_integration import (
     install_polydiff,
     parse_diff_driver_args,
-    setup_git_config,
-    write_gitattributes,
 )
 from .core.plugin_base import DiffOptions
 from .core.registry import registry
@@ -60,6 +58,17 @@ def diff(
         True, "--color/--no-color",
         help="Enable/disable colored output"
     ),
+    context_lines: int = typer.Option(
+        3, "--context-lines", "-c",
+        min=0,
+        help="Context lines for text diffs (e.g., PDF text changes)"
+    ),
+    similarity_threshold: float = typer.Option(
+        0.99, "--similarity-threshold",
+        min=0.0,
+        max=1.0,
+        help="Threshold below which files are considered changed"
+    ),
 ):
     """Compare two files directly (works with or without git)."""
     # Validate files exist
@@ -85,6 +94,8 @@ def diff(
     options = DiffOptions(
         output_format=format,
         output_path=output,
+        context_lines=context_lines,
+        similarity_threshold=similarity_threshold,
         color=color,
     )
 
diff --git a/src/polydiff/core/plugin_base.py b/src/polydiff/core/plugin_base.py
index 5d2577e..f4952df 100644
--- a/src/polydiff/core/plugin_base.py
+++ b/src/polydiff/core/plugin_base.py
@@ -13,6 +13,7 @@ class DiffOptions:
     output_format: str = "terminal"  # "terminal" | "html" | "json" | "image"
     output_path: Optional[Path] = None
     context_lines: int = 3  # for text-layer diffs inside plugins (PDF text, etc.)
+    similarity_threshold: float = 0.99  # changed if similarity < threshold
     color: bool = True
 
 
diff --git a/src/polydiff/plugins/image_diff.py b/src/polydiff/plugins/image_diff.py
index 8b79a1e..30c1573 100644
--- a/src/polydiff/plugins/image_diff.py
+++ b/src/polydiff/plugins/image_diff.py
@@ -3,7 +3,6 @@
 import base64
 import io
 from pathlib import Path
-from typing import Optional
 
 from PIL import Image
 
@@ -13,7 +12,6 @@
     compute_ssim,
     create_diff_overlay,
     create_side_by_side,
-    downsample_image,
 )
 
 
@@ -58,7 +56,7 @@ def diff(self, path_a: Path, path_b: Path, options: DiffOptions) -> DiffResult:
         side_by_side = create_side_by_side(image_a, image_b, diff_overlay)
 
         # Determine if changed
-        changed = similarity < 0.99  # Allow tiny floating point differences
+        changed = similarity < options.similarity_threshold
 
         # Build summary
         summary_parts = []
diff --git a/src/polydiff/plugins/pdf_diff.py b/src/polydiff/plugins/pdf_diff.py
index 599b2bf..4d55211 100644
--- a/src/polydiff/plugins/pdf_diff.py
+++ b/src/polydiff/plugins/pdf_diff.py
@@ -1,14 +1,14 @@
 """PDF diff plugin for polydiff."""
 
 import difflib
+from html import escape
 from pathlib import Path
-from typing import Optional
 
 import fitz  # PyMuPDF
 from PIL import Image
 
 from ..core.plugin_base import DiffOptions, DiffPlugin, DiffResult
-from ..utils.image_ops import compute_ssim, downsample_image
+from ..utils.image_ops import compute_ssim
 
 
 class PdfDiffPlugin(DiffPlugin):
@@ -90,7 +90,7 @@ def diff(self, path_a: Path, path_b: Path, options: DiffOptions) -> DiffResult:
         else:
             avg_similarity = 0.0
 
-        changed = avg_similarity < 0.99 or pages_added or pages_removed or any(
+        changed = avg_similarity < options.similarity_threshold or pages_added or pages_removed or any(
             p["text_changed"] for p in page_results
         )
 
@@ -266,7 +266,7 @@ def _build_html_output(
                 html_parts.extend([
                     '                <details>',
                     '                    <summary>View text diff</summary>',
-                    f'                    <pre>{page["text_diff"]}</pre>',
+                    f'                    <pre>{escape(page["text_diff"])}</pre>',
                     '                </details>',
                 ])
             html_parts.extend([
diff --git a/src/polydiff/plugins/xlsx_diff.py b/src/polydiff/plugins/xlsx_diff.py
index 6abb0f2..8d10135 100644
--- a/src/polydiff/plugins/xlsx_diff.py
+++ b/src/polydiff/plugins/xlsx_diff.py
@@ -1,7 +1,7 @@
 """XLSX diff plugin for polydiff."""
 
 from pathlib import Path
-from typing import Any, Optional
+from html import escape
 
 from openpyxl import load_workbook
 from openpyxl.utils import get_column_letter
@@ -72,7 +72,12 @@ def diff(self, path_a: Path, path_b: Path, options: DiffOptions) -> DiffResult:
             diff["rows_added"] or diff["rows_removed"] or diff["columns_added"] or diff["columns_removed"]
             for diff in sheet_diffs.values()
         )
-        changed = similarity < 0.99 or bool(sheets_added) or bool(sheets_removed) or has_structural_changes
+        changed = (
+            similarity < options.similarity_threshold
+            or bool(sheets_added)
+            or bool(sheets_removed)
+            or has_structural_changes
+        )
 
         # Build summary
         summary_parts = []
@@ -301,9 +306,15 @@ def _build_html_output(
         ]
 
         if sheets_added:
-            html_parts.append(f'<div class="summary added"><strong>Sheets added:</strong> {", ".join(sheets_added)}</div>')
+            html_parts.append(
+                f'<div class="summary added"><strong>Sheets added:</strong> '
+                f'{", ".join(escape(name) for name in sheets_added)}</div>'
+            )
         if sheets_removed:
-            html_parts.append(f'<div class="summary removed"><strong>Sheets removed:</strong> {", ".join(sheets_removed)}</div>')
+            html_parts.append(
+                f'<div class="summary removed"><strong>Sheets removed:</strong> '
+                f'{", ".join(escape(name) for name in sheets_removed)}</div>'
+            )
 
         # Per-sheet tables
         for sheet_name, diff in sheet_diffs.items():
@@ -312,7 +323,7 @@ def _build_html_output(
                 continue
 
             html_parts.extend([
-                f'<h3>Sheet: {sheet_name}</h3>',
+                f'<h3>Sheet: {escape(sheet_name)}</h3>',
             ])
 
             if diff["rows_added"]:
@@ -320,9 +331,15 @@ def _build_html_output(
             if diff["rows_removed"]:
                 html_parts.append(f'<div class="summary removed"><strong>Rows removed:</strong> {len(diff["rows_removed"])}</div>')
             if diff["columns_added"]:
-                html_parts.append(f'<div class="summary added"><strong>Columns added:</strong> {", ".join(diff["columns_added"])}</div>')
+                html_parts.append(
+                    f'<div class="summary added"><strong>Columns added:</strong> '
+                    f'{", ".join(escape(col) for col in diff["columns_added"])}</div>'
+                )
             if diff["columns_removed"]:
-                html_parts.append(f'<div class="summary removed"><strong>Columns removed:</strong> {", ".join(diff["columns_removed"])}</div>')
+                html_parts.append(
+                    f'<div class="summary removed"><strong>Columns removed:</strong> '
+                    f'{", ".join(escape(col) for col in diff["columns_removed"])}</div>'
+                )
 
             if changes:
                 html_parts.extend([
@@ -339,14 +356,14 @@ def _build_html_output(
                 ])
 
                 for change in changes[:100]:  # Limit to 100 in HTML
-                    old_val = str(change["old_value"]) if change["old_value"] is not None else ""
-                    new_val = str(change["new_value"]) if change["new_value"] is not None else ""
+                    old_val = escape(str(change["old_value"])) if change["old_value"] is not None else ""
+                    new_val = escape(str(change["new_value"])) if change["new_value"] is not None else ""
                     html_parts.extend([
                         '        <tr class="changed">',
-                        f'            <td>{change["cell"]}</td>',
+                        f'            <td>{escape(change["cell"])}</td>',
                         f'            <td>{old_val}</td>',
                         f'            <td>{new_val}</td>',
-                        f'            <td>{change["type"]}</td>',
+                        f'            <td>{escape(change["type"])}</td>',
                         '        </tr>',
                     ])
 
diff --git a/tests/test_pdf_diff.py b/tests/test_pdf_diff.py
index 0cf455c..075aaf7 100644
--- a/tests/test_pdf_diff.py
+++ b/tests/test_pdf_diff.py
@@ -93,3 +93,23 @@ def test_extract_text(self, plugin):
 
         assert "Hello World" in text
         assert "test document" in text
+
+    def test_html_output_escapes_text_diff(self, plugin):
+        """Test that HTML output escapes embedded text diff content."""
+        html = plugin._build_html_output(
+            page_results=[
+                {
+                    "number": 1,
+                    "visual_similarity": 0.95,
+                    "text_changed": True,
+                    "text_diff": "<script>alert('xss')</script>",
+                }
+            ],
+            pages_added=[],
+            pages_removed=[],
+            similarity=0.95,
+            summary="changed",
+        )
+
+        assert "<script>alert('xss')</script>" not in html
+        assert "&lt;script&gt;alert(&#x27;xss&#x27;)&lt;/script&gt;" in html
diff --git a/tests/test_xlsx_diff.py b/tests/test_xlsx_diff.py
index b866344..78f96ee 100644
--- a/tests/test_xlsx_diff.py
+++ b/tests/test_xlsx_diff.py
@@ -106,3 +106,34 @@ def test_terminal_output_contains_sheet_info(self, plugin, options):
         )
 
         assert "sheet" in result.terminal_output.lower() or "cell" in result.terminal_output.lower()
+
+    def test_html_output_escapes_cell_values(self, plugin):
+        """Test that HTML output escapes sheet names and cell values."""
+        html = plugin._build_html_output(
+            sheet_diffs={
+                "<sheet>": {
+                    "changes": [
+                        {
+                            "cell": "A1",
+                            "old_value": "<b>old</b>",
+                            "new_value": "<script>alert(1)</script>",
+                            "type": "value",
+                        }
+                    ],
+                    "rows_added": [],
+                    "rows_removed": [],
+                    "columns_added": [],
+                    "columns_removed": [],
+                }
+            },
+            sheets_added=["<new-sheet>"],
+            sheets_removed=[],
+            similarity=0.7,
+            summary="changed",
+        )
+
+        assert "<script>alert(1)</script>" not in html
+        assert "<b>old</b>" not in html
+        assert "&lt;script&gt;alert(1)&lt;/script&gt;" in html
+        assert "&lt;b&gt;old&lt;/b&gt;" in html
+        assert "&lt;sheet&gt;" in html