diff --git a/documentation/architecture/openspec/project.md b/documentation/architecture/openspec/project.md
index 3da5119..a8e44ee 100644
--- a/documentation/architecture/openspec/project.md
+++ b/documentation/architecture/openspec/project.md
@@ -1,31 +1,67 @@
 # Project Context
 
 ## Purpose
-[Describe your project's purpose and goals]
+This is a command-line tool for **exchanging collections of files with Large Language Models (LLMs)**. It bundles multiple files into a single clipboard-ready document while preserving directory structure and metadata, making it ideal for code reviews, project sharing, and LLM interactions. It supports interactive reviews, clipboard integration, and path protection.
 
 ## Tech Stack
-- [List your primary technologies]
-- [e.g., TypeScript, React, Node.js]
+- **Language**: Python 3.10+
+- **Build System**: Hatch
+- **Packaging**: PyInstaller (for standalone executable)
+- **Key Libraries**:
+  - `accretive` (accretive data structures)
+  - `aiofiles` (async file I/O)
+  - `detextive` (text detection)
+  - `httpx` (HTTP client)
+  - `icecream-truck` (debugging)
+  - `patiencediff` (diff generation)
+  - `pyperclip` (clipboard integration)
+  - `rich` (terminal formatting)
+  - `tiktoken` (token counting)
+  - `tomli` (TOML parsing)
+  - `tyro` (CLI argument parsing)
+  - `appcore` (application core utilities)
 
 ## Project Conventions
 
 ### Code Style
-[Describe your code style preferences, formatting rules, and naming conventions]
+- **Line Length**: 79 characters
+- **Indentation**: 4 spaces
+- **Type Hinting**: Strict type checking with `pyright` (reportUnknownArgumentType, etc. are true).
+- **Linters**:
+  - `ruff` (general linting)
+  - `isort` (import sorting)
+- **Configuration**: See `pyproject.toml` for detailed linter configurations.
 
 ### Architecture Patterns
-[Document your architectural decisions and patterns]
+- **Filesystem Organization**: See [`documentation/architecture/filesystem.rst`](../filesystem.rst) for details on the project structure.
+- **Import Hub Pattern**: Uses a centralized `__` import hub (e.g., `from . import __`) to manage internal and external dependencies.
+- **CLI Separation**: The CLI logic is separated into `cli.py` and `__main__.py` to allow independent testing and execution.
+- **Immutability**: Uses `frigid` and `accretive` for immutable and append-only data structures where appropriate.
 
 ### Testing Strategy
-[Explain your testing approach and requirements]
+- **Framework**: `pytest`
+- **Property-based Testing**: `hypothesis`
+- **Coverage**: Branch coverage enabled, enforced via CI.
+- **Doctests**: Run via Sphinx.
+- **Test Naming**: `test_[0-9][0-9][0-9]_*` pattern for test functions.
+- **Location**: All tests are located in the `tests/` directory.
 
 ### Git Workflow
-[Describe your branching strategy and commit conventions]
+- **Branching**: Pull Request (PR) based workflow.
+- **Changelog**: Managed via `towncrier`. Changelog fragments are stored in `.auxiliary/data/towncrier` and compiled into `documentation/changelog.rst`.
+- **CI/CD**: GitHub Actions for testing and linting.
 
 ## Domain Context
-[Add domain-specific knowledge that AI assistants need to understand]
+- **LLM Context Windows**: The tool is designed to optimize for limited context windows of LLMs.
+- **Mimeogram Format**: A specific textual format for bundling files that LLMs can understand and generate.
+- **Clipboard Operations**: Heavy reliance on system clipboard for data transfer between the tool and LLM interfaces (web/desktop).
+- **Path Protection**: Security mechanism to prevent LLMs from modifying sensitive files or directories.
 
 ## Important Constraints
-[List any technical, business, or regulatory constraints]
+- **Platform Support**: Must work on Linux, macOS, and Windows.
+- **Python Support**: Supports Python 3.10 to 3.14.
+- **No Automatic Sync**: The tool does not automatically sync files; it relies on manual `create` and `apply` steps.
 
 ## External Dependencies
-[Document key external services, APIs, or systems]
+- **LLM Providers**: Interacts with LLMs (OpenAI, Anthropic, etc.) indirectly via text/clipboard.
+- **GitHub**: Supports fetching files from remote GitHub URLs.