diff --git a/AGENTS.md b/AGENTS.md
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+# AI Agent Guidelines for PANOPTES Utilities
+
+This document provides guidelines for AI coding agents working with the PANOPTES Utilities (panoptes-utils) codebase. It is designed to be tool-agnostic and applicable to any AI assistant working on this project.
+
+## Project Overview
+
+PANOPTES Utilities is a Python library providing astronomical utilities for the PANOPTES ecosystem. It includes CLI tools for image processing, a configuration server, and various utility modules for astronomical data processing. This library serves as the foundation for other PANOPTES projects like [POCS](https://github.com/panoptes/POCS).
+
+**Key Characteristics:**
+- **Language:** Python 3.12+ (type hints expected)
+- **Architecture:** Modular utility library with CLI tools and services
+- **Domain:** Astronomy, image processing, configuration management
+- **Testing:** pytest with high coverage requirements
+- **Build System:** Hatch (modern Python build system)
+- **Code Style:** Ruff for linting and formatting
+
+## Essential Reading
+
+Before making changes, review these documents:
+
+1. **README:** `README.md` - Installation and basic usage
+2. **Contributing:** `CONTRIBUTING.md` - Development workflow reference
+3. **Configuration:** `pyproject.toml` - Project dependencies and configuration
+4. **Documentation:** `docs/` - Detailed documentation on modules
+
+## Project Structure
+
+```
+panoptes-utils/
+├── src/panoptes/utils/         # Main source code
+│   ├── cli/                    # Command-line interfaces
+│   │   └── main.py             # Main CLI entry point
+│   ├── config/                 # Configuration server and client
+│   │   ├── cli.py              # Config server CLI
+│   │   ├── client.py           # Config client
+│   │   └── server.py           # Config server implementation
+│   ├── images/                 # Image processing utilities
+│   ├── serial/                 # Serial device communication
+│   ├── database/               # Database utilities
+│   ├── time.py                 # Time utilities (CountdownTimer, etc.)
+│   ├── serializers.py          # Data serialization
+│   ├── horizon.py              # Horizon calculations
+│   └── utils.py                # General utilities
+├── tests/                      # Test suite
+│   ├── conftest.py             # Pytest configuration and fixtures
+│   ├── testing.yaml            # Test configuration file
+│   ├── config/                 # Config tests
+│   ├── images/                 # Image processing tests
+│   └── data/                   # Test data files
+├── docs/                       # Sphinx documentation
+├── examples/                   # Example notebooks and scripts
+└── pyproject.toml              # Project configuration and dependencies
+```
+
+## Development Workflow
+
+### 1. Understanding Changes
+
+**Before making any changes:**
+- Check if an issue exists for the change; reference it in commits/PRs
+- Review relevant module documentation to understand affected components
+- Review existing tests to understand expected behavior
+- Check `pyproject.toml` for dependencies and project configuration
+
+### 2. Code Standards
+
+**Style and Formatting:**
+- Use Ruff for linting and formatting (configured in `pyproject.toml`)
+- Line length: 110 characters
+- Quote style: double quotes
+- Follow PEP 8 conventions
+
+**Type Hints:**
+- Required for all function signatures
+- Use modern Python 3.12+ type syntax
+- Import from `typing` when necessary
+
+**Documentation:**
+- Docstrings for all public classes and functions
+- Use Google-style docstrings
+- Include examples in docstrings when helpful
+
+### 3. Testing Requirements
+
+**All code changes must include tests:**
+- Unit tests in `tests/` directory
+- Test files named `test_*.py`
+- Use pytest fixtures from `conftest.py`
+- Maintain or improve code coverage
+- Run tests locally before committing: `hatch run pytest`
+
+**Testing markers available:**
+```python
+@pytest.mark.plate_solve      # Tests requiring plate solving (astrometry.net)
+@pytest.mark.slow             # Tests that take longer to run
+```
+
+### 4. Dependencies
+
+**Adding Dependencies:**
+- Add to `dependencies` in `pyproject.toml` for runtime requirements
+- Add to `[project.optional-dependencies]` for optional features
+- Use `hatch run pip install <package>` to install in dev environment
+- Consider which extras group the dependency belongs to:
+  - `config`: Configuration server dependencies
+  - `images`: Image processing dependencies
+  - `testing`: Testing tools
+  - `docs`: Documentation building
+
+**Optional Dependencies:**
+- `config`: Flask, gevent, scalpl for configuration server
+- `images`: matplotlib, photutils, pillow for image processing
+- `testing`: pytest, coverage, and testing tools
+- `docs`: Sphinx and documentation tools
+
+### 5. Making Changes
+
+**File Editing Best Practices:**
+1. Read entire files or large sections before editing
+2. Preserve existing code style and patterns
+3. Make minimal, focused changes
+4. Validate changes by checking for errors after editing
+5. Run relevant tests to confirm functionality
+
+**Commit Messages:**
+- Clear, descriptive commit messages
+- Reference issue numbers when applicable
+- Format: `Brief description (#issue-number)`
+
+**CHANGELOG Updates:**
+- **Always update `CHANGELOG.md`** when submitting a PR
+- Add entry under the appropriate section (Added, Changed, Fixed, Removed)
+- Include PR number reference (e.g., `#123`)
+- Follow the existing format: `* Brief description of change. #PR-number`
+- Place new entries at the top of the file under a new version heading if starting a new release
+
+## Module Guidelines
+
+### Configuration Module
+
+**Location:** `src/panoptes/utils/config/`
+
+The configuration system provides centralized configuration management through a client-server architecture.
+
+**Components:**
+- `server.py`: Flask-based configuration server
+- `client.py`: Configuration client for accessing server
+- `cli.py`: Command-line interface for starting server
+
+**When modifying:**
+- Understand client-server communication protocol
+- Preserve backward compatibility with POCS and other clients
+- Test with `tests/testing.yaml` configuration
+- Ensure thread safety for concurrent access
+
+**Starting the config server:**
+```bash
+panoptes-config-server run --config-file tests/testing.yaml
+```
+
+### CLI Module
+
+**Location:** `src/panoptes/utils/cli/`
+
+Command-line tools built with Typer.
+
+**When modifying:**
+- Use Typer decorators and type hints
+- Provide clear help text and examples
+- Test commands manually and with unit tests
+- Follow existing command patterns
+
+**Available commands:**
+- `panoptes-utils image`: Image processing commands
+- `panoptes-config-server`: Configuration server management
+
+### Image Processing Module
+
+**Location:** `src/panoptes/utils/images/`
+
+Utilities for astronomical image processing, including plate solving, CR2 to FITS conversion, and image analysis.
+
+**When modifying:**
+- Understand dependencies on astrometry.net and dcraw
+- Test with sample images in `tests/images/data/`
+- Handle missing dependencies gracefully
+- Validate FITS headers and metadata
+
+**System dependencies required:**
+- `astrometry.net` for plate solving
+- `dcraw` for CR2 conversion
+- `exiftool` for metadata extraction
+
+### Time Utilities
+
+**Location:** `src/panoptes/utils/time.py`
+
+Time-related utilities including `CountdownTimer` and `wait_for_events`.
+
+**When modifying:**
+- Use `astropy.time` for astronomical time handling
+- Ensure timezone awareness (prefer UTC)
+- Test edge cases (timeouts, concurrent access)
+- Maintain compatibility with POCS usage
+
+### Serial Communication
+
+**Location:** `src/panoptes/utils/serial/` and `src/panoptes/utils/rs232.py`
+
+Serial device communication utilities.
+
+**When modifying:**
+- Handle connection errors gracefully
+- Implement appropriate timeouts
+- Test with simulator/mock devices
+- Consider thread safety
+
+## Configuration
+
+**Configuration files:** `tests/testing.yaml` (for testing)
+
+**Important configuration sections:**
+- `name`: Observatory/system name
+- `location`: Geographic coordinates
+- `directories`: Data storage locations
+- Custom sections for specific modules
+
+### Config Server
+
+The configuration server provides a REST API for centralized configuration management.
+
+**Starting the config server locally:**
+```bash
+# For development
+panoptes-config-server run --config-file tests/testing.yaml
+
+# With custom host/port
+panoptes-config-server --host 0.0.0.0 --port 8765 run --config-file tests/testing.yaml
+```
+
+**Notes:**
+- Default port is 8765
+- Server provides REST API for configuration access
+- Used by POCS and other PANOPTES components
+
+**When modifying configuration:**
+- Maintain backward compatibility when possible
+- Update example configs in `tests/`
+- Document new configuration options
+- Validate configuration structure
+- Restart config server after modifying config files
+
+## Common Tasks
+
+### Adding a New CLI Command
+
+1. Add command to `src/panoptes/utils/cli/main.py` or create new module
+2. Use Typer decorators for command definition
+3. Add help text, examples, and type hints
+4. Write tests for the command
+5. Update documentation in `docs/cli.rst`
+
+### Adding a New Utility Function
+
+1. Choose appropriate module (`time.py`, `utils.py`, etc.)
+2. Implement function with type hints
+3. Write comprehensive docstring
+4. Add unit tests
+5. Consider if it should be public API
+6. Update module documentation if needed
+
+### Adding Image Processing Features
+
+1. Implement in `src/panoptes/utils/images/`
+2. Handle optional dependencies gracefully
+3. Test with sample images
+4. Validate FITS headers and metadata
+5. Update CLI if user-facing
+
+## Error Handling
+
+**Best Practices:**
+- Use specific exception types from `panoptes.utils.error`
+- Provide informative error messages
+- Log errors appropriately (use `loguru`)
+- Clean up resources in error cases
+- Consider graceful degradation for optional features
+- Don't silently catch exceptions
+
+## Logging
+
+**The project uses `loguru` for logging:**
+
+```python
+from loguru import logger
+
+logger.info("Informational message")
+logger.warning("Warning message")
+logger.error("Error message")
+logger.debug("Debug details")
+```
+
+**Guidelines:**
+- Import `logger` from `loguru`
+- Log important operations and state changes
+- Include context in log messages
+- Use appropriate log levels
+- Don't log sensitive information
+- Consider log volume (avoid spam)
+
+## Testing Strategy
+
+### Test Organization
+
+```
+tests/
+├── test_*.py              # Main test files
+├── conftest.py            # Pytest configuration and fixtures
+├── testing.yaml           # Test configuration
+├── config/                # Config module tests
+├── images/                # Image processing tests
+│   └── data/              # Sample images for testing
+└── data/                  # Test data files
+```
+
+### Writing Tests
+
+**Good test characteristics:**
+- Isolated (don't depend on other tests)
+- Repeatable (same result every time)
+- Fast (use mocks for slow operations)
+- Clear (obvious what's being tested)
+- Comprehensive (test edge cases)
+
+**Use fixtures:**
+```python
+def test_config_client(config_host, config_port):
+    """Test config client connection."""
+    # Use fixtures from conftest.py
+```
+
+### Running Tests
+
+```bash
+# Run all tests
+hatch run pytest
+
+# Run specific test file
+hatch run pytest tests/test_time.py
+
+# Run specific test
+hatch run pytest tests/test_time.py::test_countdown_timer
+
+# Run with markers
+hatch run pytest -m "not plate_solve"
+
+# Run with coverage (default)
+hatch run pytest
+```
+
+## Documentation
+
+### Docstring Format (Google Style)
+
+```python
+def function_name(param1: str, param2: int) -> bool:
+    """Brief one-line description.
+    
+    Longer description if needed. Explain what the function does,
+    why it exists, and any important details.
+    
+    Args:
+        param1: Description of param1
+        param2: Description of param2
+        
+    Returns:
+        Description of return value
+        
+    Raises:
+        ValueError: When this happens
+        RuntimeError: When that happens
+        
+    Examples:
+        >>> function_name("test", 42)
+        True
+    """
+```
+
+### Documentation Updates
+
+When making changes, update:
+- **`CHANGELOG.md`** for all PRs (required)
+- Inline code comments for complex logic
+- Docstrings for API changes
+- Sphinx docs in `docs/` for major features
+- README for installation/usage changes
+- Examples for new features
+
+## Security Considerations
+
+- Validate external input (file paths, coordinates, etc.)
+- Handle credentials securely (never commit secrets)
+- Sanitize user-provided configuration
+- Validate file operations (path traversal)
+- Consider dependency vulnerabilities
+- Sanitize shell commands if used
+
+## Performance Considerations
+
+- Utilities may be called frequently by POCS
+- Avoid blocking operations where possible
+- Use appropriate timeout values
+- Consider memory usage for image processing
+- Optimize hot paths
+- Cache expensive computations when appropriate
+
+## Common Pitfalls
+
+1. **System Dependencies:** Not all systems have astrometry.net, dcraw installed
+2. **Config Server Availability:** Code should handle missing config server gracefully
+3. **Optional Dependencies:** Features using optional deps should fail gracefully
+4. **File Paths:** Use `pathlib.Path`, handle both absolute and relative paths
+5. **Time Zones:** Use UTC for all astronomical calculations
+6. **Astropy Units:** Use units consistently (especially angles)
+7. **Thread Safety:** Consider concurrent access to shared resources
+
+## Astronomy Domain Knowledge
+
+**Key concepts to understand:**
+- **Alt/Az vs. RA/Dec:** Different coordinate systems
+- **Sidereal Time:** Astronomical time standard
+- **Field of View:** Area of sky visible to camera
+- **Plate Solving:** Determining image coordinates from stars
+- **FITS Format:** Flexible Image Transport System for astronomical images
+- **WCS:** World Coordinate System for image coordinates
+
+**Useful libraries:**
+- `astropy`: Astronomical calculations, units, and FITS handling
+- `astroplan`: Observation planning utilities
+- `photutils`: Photometry and image analysis
+- `sep`: Source extraction and photometry
+
+## Getting Help
+
+- **Documentation:** https://panoptes-utils.readthedocs.io
+- **POCS Documentation:** https://pocs.readthedocs.io
+- **Forum:** https://forum.projectpanoptes.org
+- **Issues:** https://github.com/panoptes/panoptes-utils/issues
+- **Code of Conduct:** `CODE_OF_CONDUCT.md`
+
+## AI Agent-Specific Tips
+
+### Context Gathering
+
+1. **Start broad, then narrow:**
+   - Read README and module documentation first
+   - Understand component relationships
+   - Then dive into specific files
+
+2. **Search effectively:**
+   - Use semantic search for concepts
+   - Use grep for specific strings/patterns
+   - Check test files for usage examples
+
+3. **Understand before changing:**
+   - Read the full function/class
+   - Check call sites to understand usage
+   - Review related tests
+
+### Making Changes
+
+1. **Validate assumptions:**
+   - Check current behavior with tests
+   - Verify understanding of requirements
+   - Consider edge cases
+
+2. **Incremental approach:**
+   - Make small, testable changes
+   - Run tests frequently
+   - Fix errors as they appear
+
+3. **Preserve intent:**
+   - Maintain existing patterns
+   - Don't over-engineer solutions
+   - Keep changes focused
+
+### Communication
+
+1. **Be specific:**
+   - Reference exact file paths
+   - Quote relevant code sections
+   - Explain reasoning for changes
+
+2. **Show your work:**
+   - Explain what you searched for
+   - Describe what you found
+   - Outline your approach
+
+3. **Ask when uncertain:**
+   - Clarify requirements if ambiguous
+   - Confirm understanding of domain concepts
+   - Request feedback on approach
+
+## Quick Reference
+
+### Common Commands
+
+```bash
+# Create development environment
+hatch env create
+
+# Install optional extras
+hatch run pip install -e ".[config,images,testing]"
+
+# Run tests
+hatch run pytest
+
+# Run specific test file
+hatch run pytest tests/test_utils.py
+
+# Check code style
+hatch run lint
+
+# Format code
+hatch run fmt
+
+# Check formatting
+hatch run fmt-check
+
+# Build package
+hatch build
+
+# Start config server
+panoptes-config-server run --config-file tests/testing.yaml
+
+# View CLI help
+panoptes-utils --help
+panoptes-utils image --help
+```
+
+### File Locations
+
+- Time utilities: `src/panoptes/utils/time.py`
+- Config server: `src/panoptes/utils/config/server.py`
+- Config client: `src/panoptes/utils/config/client.py`
+- CLI: `src/panoptes/utils/cli/main.py`
+- Image processing: `src/panoptes/utils/images/`
+- Tests: `tests/`
+- Test config: `tests/testing.yaml`
+
+### Important Conventions
+
+- Use `logger` from `loguru` for logging
+- Use `pathlib.Path` for file paths
+- Use `astropy.units` for physical quantities
+- Use type hints on all functions
+- Write tests for all new code
+- Update documentation for API changes
+
+---
+
+**Remember:** PANOPTES Utilities is a foundational library used by POCS and other PANOPTES projects. Changes here can affect multiple downstream projects, so maintain backward compatibility and thorough testing.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1fd66230..2f1ce995 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,16 @@
 # CHANGELOG
 
+## Unreleased
+
+### Added
+
+* AI agent guidelines document (`AGENTS.md`) with comprehensive development workflow and coding standards. #331
+* CHANGELOG update requirement to contributor guidelines in `AGENTS.md`. #331
+
+### Changed
+
+* Line-length configuration from 100 to 110 characters in `pyproject.toml` and documentation. #331
+
 ## 0.2.53 - 2025-10-21
 
 ## Added
diff --git a/pyproject.toml b/pyproject.toml
index 049a624c..034e8ebe 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -148,7 +148,7 @@ exclude_lines = [
 ]
 
 [tool.ruff]
-line-length = 100
+line-length = 110
 target-version = "py312"
 extend-exclude = [
     "notebooks",