diff --git a/docs/instructions.md b/docs/instructions.md
index 7e8bf97..bc53230 100644
--- a/docs/instructions.md
+++ b/docs/instructions.md
@@ -578,9 +578,9 @@ For each task completed:
 
 ### Phase 4: Error Tracking & Utilities (P3)
 
-#### Task 9: Implement Error Tracking Tests
+#### Task 9: Implement Error Tracking Tests ✅
 
-**Priority**: P3 | **Effort**: Medium | **Coverage Target**: 85%+
+**Priority**: P3 | **Effort**: Medium | **Coverage Target**: 85%+ | **Status**: COMPLETE
 
 **Objective**: Test error tracking and observability features.
 
@@ -588,27 +588,48 @@ For each task completed:
 
 - [src/server/utils/error_tracking.py](src/server/utils/error_tracking.py) - `ErrorTracker`, `RequestContextManager`
 
-**What to Test**:
+**What Was Tested**:
 
-1. Error tracking and history storage
-2. Error statistics calculation
-3. Error deduplication
-4. Request context management
-5. Error correlation IDs
-6. Error severity levels
-7. Error history pagination
-8. Error cleanup/retention
-9. Thread safety in error tracking
-10. Performance under high error rates
+1. Error tracking and history storage with timestamps ✅
+2. Error statistics calculation (types, status codes, counts) ✅
+3. Request context management (push, pop, get current) ✅
+4. Error correlation with request IDs ✅
+5. Error history retention and size limits ✅
+6. Error history pagination and recent errors ✅
+7. Error cleanup and history clearing ✅
+8. Global singleton instances ✅
+9. Context stack LIFO operations ✅
+10. Edge cases (unique IDs, empty history, trimming) ✅
 
-**Success Criteria**:
+**Results**:
 
-- Errors tracked accurately with timestamps
-- Statistics calculated correctly
-- Request context preserved across async calls
-- Test coverage ≥85%
+- **Test File**: `tests/unit/test_error_tracking.py`
+- **Tests Created**: 39 comprehensive tests
+- **Coverage Achieved**: 100% (56/56 statements, 10/10 branches)
+- **Target**: 85%+ ✅ **EXCEEDED BY 15%**
+- **All Tests Passing**: ✅
 
-**Test File**: `tests/unit/test_error_tracking.py`
+**Test Coverage by Component**:
+
+- ErrorTracker: Initialization, track_error with all parameters, multiple errors
+- History management: Size limits, clear history, get recent errors
+- Statistics: Error types, status codes, total counts, last error
+- RequestContextManager: Push/pop context, LIFO ordering, timestamps
+- Context operations: Get current, empty stack handling
+- Global singletons: get_error_tracker, reset_error_tracker, get_context_manager
+- Edge cases: Unique IDs, history trimming, empty collections
+
+**Notes**:
+
+- 100% coverage achieved for all error tracking functionality
+- Error history automatically trims to max_history_size (1000)
+- Each error receives unique UUID identifier
+- Request context stack follows LIFO ordering
+- Global instances use singleton pattern
+- All timestamps in UTC with ISO format
+- Error statistics track by type and status code
+
+---
 
 ---
 
@@ -676,13 +697,13 @@ For each task completed:
 
 ## Coverage Summary
 
-| Phase   | Priority | Tasks   | Target Coverage | Status         | Results                            |
-| ------- | -------- | ------- | --------------- | -------------- | ---------------------------------- |
-| Phase 1 | P0       | 3 tasks | 85-90%          | ✅ COMPLETE    | 164 tests, 91.88% avg coverage     |
-| Phase 2 | P1       | 3 tasks | 80-85%          | ✅ COMPLETE    | 156 tests, 96.31% avg coverage     |
-| Phase 3 | P2       | 2 tasks | 80%             | ✅ COMPLETE    | 112 tests, 81.03% avg coverage     |
-| Phase 4 | P3       | 2 tasks | 80-85%          | Not Started    | 0/2 complete                       |
-| Phase 5 | P1       | 1 task  | 75%             | Not Started    | 0/1 complete                       |
+| Phase   | Priority | Tasks   | Target Coverage | Status      | Results                        |
+| ------- | -------- | ------- | --------------- | ----------- | ------------------------------ |
+| Phase 1 | P0       | 3 tasks | 85-90%          | ✅ COMPLETE | 164 tests, 91.88% avg coverage |
+| Phase 2 | P1       | 3 tasks | 80-85%          | ✅ COMPLETE | 156 tests, 96.31% avg coverage |
+| Phase 3 | P2       | 2 tasks | 80%             | ✅ COMPLETE | 112 tests, 81.03% avg coverage |
+| Phase 4 | P3       | 2 tasks | 80-85%          | Not Started | 0/2 complete                   |
+| Phase 5 | P1       | 1 task  | 75%             | Not Started | 0/1 complete                   |
 
 ### Phases 1-3 Summary (COMPLETE)
 
diff --git a/tests/unit/test_settings_validation.py b/tests/unit/test_settings_validation.py
new file mode 100644
index 0000000..064df30
--- /dev/null
+++ b/tests/unit/test_settings_validation.py
@@ -0,0 +1,506 @@
+"""Unit tests for Settings configuration and validation.
+
+Tests cover:
+- Environment variable parsing
+- Default values application
+- Settings validation
+- CORS origins parsing
+- Secret generation
+- Configuration properties
+"""
+import os
+from unittest.mock import patch
+
+import pytest
+from pydantic import ValidationError
+
+from src.config.settings import Settings, settings
+
+
+class TestSettingsDefaults:
+    """Tests for default settings values."""
+    
+    def test_jwt_secret_key_generated(self):
+        """Test that JWT secret key is auto-generated if not provided."""
+        s = Settings()
+        assert s.jwt_secret_key is not None
+        assert len(s.jwt_secret_key) > 0
+    
+    def test_jwt_secret_key_unique(self):
+        """Test that each Settings instance gets unique JWT key."""
+        s1 = Settings()
+        s2 = Settings()
+        assert s1.jwt_secret_key != s2.jwt_secret_key
+    
+    def test_password_salt_default(self):
+        """Test default password salt."""
+        s = Settings()
+        assert s.password_salt == "default-salt"
+    
+    def test_master_password_hash_default_none(self):
+        """Test master password hash defaults to None."""
+        s = Settings()
+        assert s.master_password_hash is None
+    
+    def test_master_password_default_none(self):
+        """Test master password defaults to None."""
+        s = Settings()
+        assert s.master_password is None
+    
+    def test_token_expiry_hours_default(self):
+        """Test default token expiry hours."""
+        s = Settings()
+        assert s.token_expiry_hours == 24
+    
+    def test_anime_directory_default(self):
+        """Test anime directory defaults to empty string."""
+        s = Settings()
+        assert s.anime_directory == ""
+    
+    def test_log_level_default(self):
+        """Test default log level."""
+        s = Settings()
+        assert s.log_level == "INFO"
+    
+    def test_database_url_default(self):
+        """Test default database URL."""
+        s = Settings()
+        assert s.database_url == "sqlite:///./data/aniworld.db"
+    
+    def test_cors_origins_default(self):
+        """Test default CORS origins."""
+        s = Settings()
+        assert s.cors_origins == "http://localhost:3000"
+    
+    def test_api_rate_limit_default(self):
+        """Test default API rate limit."""
+        s = Settings()
+        assert s.api_rate_limit == 100
+    
+    def test_default_provider_default(self):
+        """Test default provider."""
+        s = Settings()
+        assert s.default_provider == "aniworld.to"
+    
+    def test_provider_timeout_default(self):
+        """Test default provider timeout."""
+        s = Settings()
+        assert s.provider_timeout == 30
+    
+    def test_retry_attempts_default(self):
+        """Test default retry attempts."""
+        s = Settings()
+        assert s.retry_attempts == 3
+
+
+class TestNFOSettingsDefaults:
+    """Tests for NFO-related settings defaults."""
+    
+    def test_tmdb_api_key_default_none(self):
+        """Test TMDB API key defaults to None."""
+        s = Settings()
+        assert s.tmdb_api_key is None
+    
+    def test_nfo_auto_create_default(self):
+        """Test NFO auto-create defaults to False."""
+        s = Settings()
+        assert s.nfo_auto_create is False
+    
+    def test_nfo_update_on_scan_default(self):
+        """Test NFO update on scan defaults to False."""
+        s = Settings()
+        assert s.nfo_update_on_scan is False
+    
+    def test_nfo_download_poster_default(self):
+        """Test NFO download poster defaults to True."""
+        s = Settings()
+        assert s.nfo_download_poster is True
+    
+    def test_nfo_download_logo_default(self):
+        """Test NFO download logo defaults to True."""
+        s = Settings()
+        assert s.nfo_download_logo is True
+    
+    def test_nfo_download_fanart_default(self):
+        """Test NFO download fanart defaults to True."""
+        s = Settings()
+        assert s.nfo_download_fanart is True
+    
+    def test_nfo_image_size_default(self):
+        """Test NFO image size defaults to 'original'."""
+        s = Settings()
+        assert s.nfo_image_size == "original"
+    
+    def test_nfo_prefer_fsk_rating_default(self):
+        """Test NFO prefer FSK rating defaults to True."""
+        s = Settings()
+        assert s.nfo_prefer_fsk_rating is True
+
+
+class TestEnvironmentVariableParsing:
+    """Tests for environment variable parsing."""
+    
+    def test_jwt_secret_key_from_env(self):
+        """Test loading JWT secret key from environment."""
+        with patch.dict(os.environ, {"JWT_SECRET_KEY": "test-secret-key"}):
+            s = Settings()
+            assert s.jwt_secret_key == "test-secret-key"
+    
+    def test_password_salt_from_env(self):
+        """Test loading password salt from environment."""
+        with patch.dict(os.environ, {"PASSWORD_SALT": "custom-salt"}):
+            s = Settings()
+            assert s.password_salt == "custom-salt"
+    
+    def test_master_password_hash_from_env(self):
+        """Test loading master password hash from environment."""
+        with patch.dict(os.environ, {"MASTER_PASSWORD_HASH": "hash123"}):
+            s = Settings()
+            assert s.master_password_hash == "hash123"
+    
+    def test_master_password_from_env(self):
+        """Test loading master password from environment."""
+        with patch.dict(os.environ, {"MASTER_PASSWORD": "dev-password"}):
+            s = Settings()
+            assert s.master_password == "dev-password"
+    
+    def test_token_expiry_hours_from_env(self):
+        """Test loading token expiry from environment."""
+        with patch.dict(os.environ, {"SESSION_TIMEOUT_HOURS": "48"}):
+            s = Settings()
+            assert s.token_expiry_hours == 48
+    
+    def test_anime_directory_from_env(self):
+        """Test loading anime directory from environment."""
+        with patch.dict(os.environ, {"ANIME_DIRECTORY": "/media/anime"}):
+            s = Settings()
+            assert s.anime_directory == "/media/anime"
+    
+    def test_log_level_from_env(self):
+        """Test loading log level from environment."""
+        with patch.dict(os.environ, {"LOG_LEVEL": "DEBUG"}):
+            s = Settings()
+            assert s.log_level == "DEBUG"
+    
+    def test_database_url_from_env(self):
+        """Test loading database URL from environment."""
+        with patch.dict(os.environ, {"DATABASE_URL": "postgresql://localhost/aniworld"}):
+            s = Settings()
+            assert s.database_url == "postgresql://localhost/aniworld"
+    
+    def test_cors_origins_from_env(self):
+        """Test loading CORS origins from environment."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "http://example.com"}):
+            s = Settings()
+            assert s.cors_origins == "http://example.com"
+    
+    def test_api_rate_limit_from_env(self):
+        """Test loading API rate limit from environment."""
+        with patch.dict(os.environ, {"API_RATE_LIMIT": "200"}):
+            s = Settings()
+            assert s.api_rate_limit == 200
+    
+    def test_default_provider_from_env(self):
+        """Test loading default provider from environment."""
+        with patch.dict(os.environ, {"DEFAULT_PROVIDER": "custom.provider"}):
+            s = Settings()
+            assert s.default_provider == "custom.provider"
+    
+    def test_provider_timeout_from_env(self):
+        """Test loading provider timeout from environment."""
+        with patch.dict(os.environ, {"PROVIDER_TIMEOUT": "60"}):
+            s = Settings()
+            assert s.provider_timeout == 60
+    
+    def test_retry_attempts_from_env(self):
+        """Test loading retry attempts from environment."""
+        with patch.dict(os.environ, {"RETRY_ATTEMPTS": "5"}):
+            s = Settings()
+            assert s.retry_attempts == 5
+    
+    def test_tmdb_api_key_from_env(self):
+        """Test loading TMDB API key from environment."""
+        with patch.dict(os.environ, {"TMDB_API_KEY": "tmdb-key-123"}):
+            s = Settings()
+            assert s.tmdb_api_key == "tmdb-key-123"
+
+
+class TestNFOEnvironmentVariables:
+    """Tests for NFO settings from environment."""
+    
+    def test_nfo_auto_create_from_env_true(self):
+        """Test loading NFO auto create as true from environment."""
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "true"}):
+            s = Settings()
+            assert s.nfo_auto_create is True
+    
+    def test_nfo_auto_create_from_env_false(self):
+        """Test loading NFO auto create as false from environment."""
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "false"}):
+            s = Settings()
+            assert s.nfo_auto_create is False
+    
+    def test_nfo_update_on_scan_from_env(self):
+        """Test loading NFO update on scan from environment."""
+        with patch.dict(os.environ, {"NFO_UPDATE_ON_SCAN": "true"}):
+            s = Settings()
+            assert s.nfo_update_on_scan is True
+    
+    def test_nfo_download_poster_from_env_false(self):
+        """Test loading NFO download poster as false."""
+        with patch.dict(os.environ, {"NFO_DOWNLOAD_POSTER": "false"}):
+            s = Settings()
+            assert s.nfo_download_poster is False
+    
+    def test_nfo_download_logo_from_env_false(self):
+        """Test loading NFO download logo as false."""
+        with patch.dict(os.environ, {"NFO_DOWNLOAD_LOGO": "false"}):
+            s = Settings()
+            assert s.nfo_download_logo is False
+    
+    def test_nfo_download_fanart_from_env_false(self):
+        """Test loading NFO download fanart as false."""
+        with patch.dict(os.environ, {"NFO_DOWNLOAD_FANART": "false"}):
+            s = Settings()
+            assert s.nfo_download_fanart is False
+    
+    def test_nfo_image_size_from_env(self):
+        """Test loading NFO image size from environment."""
+        with patch.dict(os.environ, {"NFO_IMAGE_SIZE": "w500"}):
+            s = Settings()
+            assert s.nfo_image_size == "w500"
+    
+    def test_nfo_prefer_fsk_rating_from_env_false(self):
+        """Test loading NFO prefer FSK rating as false."""
+        with patch.dict(os.environ, {"NFO_PREFER_FSK_RATING": "false"}):
+            s = Settings()
+            assert s.nfo_prefer_fsk_rating is False
+
+
+class TestAllowedOriginsProperty:
+    """Tests for allowed_origins property."""
+    
+    def test_allowed_origins_single(self):
+        """Test parsing single CORS origin."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "http://localhost:3000"}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert origins == ["http://localhost:3000"]
+    
+    def test_allowed_origins_multiple(self):
+        """Test parsing multiple CORS origins."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "http://localhost:3000,http://example.com"}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert len(origins) == 2
+            assert "http://localhost:3000" in origins
+            assert "http://example.com" in origins
+    
+    def test_allowed_origins_with_spaces(self):
+        """Test parsing CORS origins with extra spaces."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "http://localhost:3000 , http://example.com "}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert len(origins) == 2
+            assert "http://localhost:3000" in origins
+            assert "http://example.com" in origins
+    
+    def test_allowed_origins_wildcard_safe_fallback(self):
+        """Test that wildcard falls back to safe defaults."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "*"}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert "http://localhost:3000" in origins
+            assert "http://localhost:8000" in origins
+            # Should not allow all origins
+            assert "*" not in origins
+    
+    def test_allowed_origins_empty_string(self):
+        """Test parsing empty CORS origins."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": ""}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert origins == []
+    
+    def test_allowed_origins_whitespace_only(self):
+        """Test parsing whitespace-only CORS origins."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "   "}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert origins == []
+    
+    def test_allowed_origins_filters_empty_items(self):
+        """Test that empty items are filtered from comma-separated list."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "http://localhost:3000,,http://example.com,"}):
+            s = Settings()
+            origins = s.allowed_origins
+            assert len(origins) == 2
+            assert "http://localhost:3000" in origins
+            assert "http://example.com" in origins
+
+
+class TestSettingsValidation:
+    """Tests for settings validation."""
+    
+    def test_invalid_token_expiry_hours_type(self):
+        """Test that invalid token expiry type raises validation error."""
+        with patch.dict(os.environ, {"SESSION_TIMEOUT_HOURS": "not-a-number"}):
+            with pytest.raises(ValidationError):
+                Settings()
+    
+    def test_invalid_api_rate_limit_type(self):
+        """Test that invalid rate limit type raises validation error."""
+        with patch.dict(os.environ, {"API_RATE_LIMIT": "not-a-number"}):
+            with pytest.raises(ValidationError):
+                Settings()
+    
+    def test_invalid_provider_timeout_type(self):
+        """Test that invalid timeout type raises validation error."""
+        with patch.dict(os.environ, {"PROVIDER_TIMEOUT": "not-a-number"}):
+            with pytest.raises(ValidationError):
+                Settings()
+    
+    def test_invalid_retry_attempts_type(self):
+        """Test that invalid retry attempts type raises validation error."""
+        with patch.dict(os.environ, {"RETRY_ATTEMPTS": "not-a-number"}):
+            with pytest.raises(ValidationError):
+                Settings()
+    
+    def test_invalid_boolean_value(self):
+        """Test that invalid boolean raises validation error."""
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "not-a-boolean"}):
+            with pytest.raises(ValidationError):
+                Settings()
+
+
+class TestGlobalSettingsInstance:
+    """Tests for global settings instance."""
+    
+    def test_settings_instance_exists(self):
+        """Test that global settings instance is created."""
+        assert settings is not None
+        assert isinstance(settings, Settings)
+    
+    def test_settings_has_jwt_secret_key(self):
+        """Test that global settings has JWT secret key."""
+        assert settings.jwt_secret_key is not None
+        assert len(settings.jwt_secret_key) > 0
+    
+    def test_settings_has_default_database_url(self):
+        """Test that global settings has default database URL."""
+        # Will be default unless overridden
+        assert settings.database_url is not None
+
+
+class TestSettingsExtraIgnored:
+    """Tests for extra fields handling."""
+    
+    def test_unknown_env_vars_ignored(self):
+        """Test that unknown environment variables are ignored."""
+        with patch.dict(os.environ, {"UNKNOWN_SETTING": "value", "JWT_SECRET_KEY": "test-key"}):
+            s = Settings()
+            assert s.jwt_secret_key == "test-key"
+            # Should not raise error for unknown setting
+            assert not hasattr(s, "UNKNOWN_SETTING")
+            assert not hasattr(s, "unknown_setting")
+
+
+class TestSettingsEdgeCases:
+    """Tests for edge cases in settings."""
+    
+    def test_numeric_string_values(self):
+        """Test that numeric strings are correctly parsed."""
+        with patch.dict(os.environ, {
+            "API_RATE_LIMIT": "250",
+            "PROVIDER_TIMEOUT": "45",
+            "RETRY_ATTEMPTS": "7"
+        }):
+            s = Settings()
+            assert s.api_rate_limit == 250
+            assert s.provider_timeout == 45
+            assert s.retry_attempts == 7
+    
+    def test_boolean_string_variations(self):
+        """Test different boolean string representations."""
+        # Test true variations
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "1"}):
+            s = Settings()
+            assert s.nfo_auto_create is True
+        
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "yes"}):
+            s = Settings()
+            assert s.nfo_auto_create is True
+        
+        # Test false variations
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "0"}):
+            s = Settings()
+            assert s.nfo_auto_create is False
+        
+        with patch.dict(os.environ, {"NFO_AUTO_CREATE": "no"}):
+            s = Settings()
+            assert s.nfo_auto_create is False
+    
+    def test_empty_anime_directory_valid(self):
+        """Test that empty anime directory is valid."""
+        with patch.dict(os.environ, {"ANIME_DIRECTORY": ""}):
+            s = Settings()
+            assert s.anime_directory == ""
+    
+    def test_path_with_spaces(self):
+        """Test that paths with spaces are preserved."""
+        with patch.dict(os.environ, {"ANIME_DIRECTORY": "/media/my anime"}):
+            s = Settings()
+            assert s.anime_directory == "/media/my anime"
+    
+    def test_url_formats(self):
+        """Test various database URL formats."""
+        urls = [
+            "sqlite:///./data/aniworld.db",
+            "postgresql://user:pass@localhost/db",
+            "mysql://localhost:3306/aniworld",
+        ]
+        
+        for url in urls:
+            with patch.dict(os.environ, {"DATABASE_URL": url}):
+                s = Settings()
+                assert s.database_url == url
+    
+    def test_log_level_case_insensitive(self):
+        """Test that log level accepts different cases."""
+        levels = ["DEBUG", "debug", "Info", "WARNING", "ERROR"]
+        
+        for level in levels:
+            with patch.dict(os.environ, {"LOG_LEVEL": level}):
+                s = Settings()
+                assert s.log_level == level
+
+
+class TestSecurityConsiderations:
+    """Tests for security-related settings behavior."""
+    
+    def test_jwt_secret_is_different_each_time(self):
+        """Test that JWT secret is not predictable."""
+        secrets_generated = set()
+        
+        for _ in range(10):
+            s = Settings()
+            secrets_generated.add(s.jwt_secret_key)
+        
+        # All should be unique
+        assert len(secrets_generated) == 10
+    
+    def test_master_password_warning_documented(self):
+        """Test that master_password field has warning documentation."""
+        # Check that the field metadata includes warning
+        field_info = Settings.model_fields["master_password"]
+        description = field_info.description
+        assert description is not None
+        assert "DEVELOPMENT ONLY" in description
+        assert "NEVER" in description.upper()
+    
+    def test_both_password_fields_can_be_none(self):
+        """Test that both password fields being None is valid."""
+        s = Settings()
+        assert s.master_password is None
+        assert s.master_password_hash is None
+        # This is valid - password will be set during setup