diff --git a/openspec/changes/declpac-cli-tool/.openspec.yaml b/openspec/changes/declpac-cli-tool/.openspec.yaml
new file mode 100644
index 0000000..e14f322
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/.openspec.yaml
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-04-13
diff --git a/openspec/changes/declpac-cli-tool/design.md b/openspec/changes/declpac-cli-tool/design.md
new file mode 100644
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+++ b/openspec/changes/declpac-cli-tool/design.md
@@ -0,0 +1,109 @@
+## Context
+
+Pacman, Arch Linux's package manager, lacks declarative package management and
+doesn't support partial upgrades. Users managing system packages from scripts
+or configuration files need a way to ensure their system state matches a declared
+package list, with all packages at their latest available versions.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Provide a declarative interface for pacman package management through
+  command-line interface
+- Support flexible input sources (stdin and multiple state files) with
+  additive merging
+- **Automatically resolve transitive dependencies (users specify only direct packages)**
+- Enforce full package upgrades (no partial upgrades) to prevent version
+  mismatches
+- Generate machine-readable output suitable for automated scripting
+- Enable AI-driven implementation for new Go developers
+
+**Non-Goals:**
+- Package dependency resolution or smart upgrade scheduling
+- Transaction rollback capabilities
+- Pretty terminal output or interactive prompts
+- Support for partial upgrades or selective package versions
+- State persistence (tool only syncs, doesn't save state)
+
+## Decisions
+
+**Language: Go**
+- Rationale: User wants modern CLI tool with native package management
+  capabilities
+- Go provides strong standard library, easy command-line parsing, and
+  excellent for system-level operations
+- User unfamiliar with Go - implementation will be AI-driven with detailed
+  documentation
+
+**Input Parsing Approach**
+- Parse whitespace, tabs, newlines for package names
+- Support multiple --state files: all additive including with stdin
+- Validate package names against pacman available packages (optional validation)
+- Empty state detection: print error to stderr and exit with code 1 (abort)
+
+**State Merging Logic**
+- All inputs are additive: combine all packages from stdin and all state files
+- No conflict resolution: missing packages are added, duplicates accumulate
+- Order-independent: inputs don't override each other
+
+**Pacman Interaction**
+- Use os/exec.Command to run pacman with -Sy (sync databases) and -S flag
+- Run pacman -Syu with all target packages to ensure full upgrade
+- Capture stderr/stdout for error reporting and machine output
+- Detect pacman exit codes and translate to tool exit codes
+
+**Error Handling Strategy**
+- Parse pacman error messages from stderr output
+- Distinguish between package-not-found (warning) vs. execution failures (errors)
+- Return appropriate exit codes: 0 for success, non-zero for errors
+- Include error details in output for scripting purposes
+
+**AUR Integration**
+- For packages not found in pacman repositories, check if available in AUR
+- Use makepkg directly to build and install AUR packages (no AUR helpers)
+- Clone AUR git repo to temp directory
+- Run `makepkg -si` in temp directory for installation
+- Capture stdout/stderr for output and error handling
+- Report error to stderr if package not found in pacman or AUR
+
+**Dependency Resolution**
+- Use pacman's dependency resolution by passing all declared packages to `pacman -Syu`
+- Pacman automatically resolves and includes transitive dependencies
+- For AUR packages, makepkg handles dependency resolution during build
+- No custom dependency resolution logic required - delegate to pacman/makepkg
+
+**Explicit Marking & Orphan Cleanup**
+- Before syncing, get list of all currently installed packages
+- Mark declared state packages as explicitly installed via `pacman -D --explicit <pkg>`
+- All other installed packages remain as non-explicit (dependencies)
+- After sync completes, run `pacman -Rns $(pacman -Qdtq)` to remove orphaned packages
+- Pacman -Rns $(pacman -Qdtq) only removes packages that are not explicitly
+  installed and not required
+- Capture and report number of packages removed during cleanup
+
+**Package Version Management**
+- Always force full system upgrade via `pacman -Syu <packages>`
+- Pacman handles version selection automatically, ensuring latest versions
+- No semantic version comparison or pinning logic required
+
+## Risks / Trade-offs
+
+**Known Risks:**
+- [User unfamiliarity with Go] → Mitigation: Provide complete implementation
+  with detailed comments; user can review and run without understanding deeply
+- [Pacman error message parsing complexity] → Mitigation: Use broad error
+  pattern matching; include error output as-is for debugging
+- [Empty state triggers abort] → Mitigation: Print error to stderr and exit
+  with code 1 instead of proceeding with empty state
+- [Additive merging could accumulate duplicates] → Mitigation: Accept as
+  design choice; pacman handles duplicates gracefully
+- [Dependency conflicts could occur] → Mitigation: Let pacman handle standard
+  conflicts; tool won't implement complex dependency resolution
+
+**Trade-offs:**
+- No conflict resolution: simpler merging but may include packages the system
+  rejects
+- Additive vs replacement: safer but less predictable for users expecting
+  replacements
+- No user prompts: fully automated for scripting but could be risky without
+  warnings
diff --git a/openspec/changes/declpac-cli-tool/proposal.md b/openspec/changes/declpac-cli-tool/proposal.md
new file mode 100644
index 0000000..6345af3
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+++ b/openspec/changes/declpac-cli-tool/proposal.md
@@ -0,0 +1,39 @@
+## Why
+
+Pacman doesn't support declarative package management or partial upgrades,
+making it challenging to maintain consistent system states. This tool provides
+a clean, scriptable interface to synchronize the system with a declared package
+list, ensuring all packages are at the latest version.
+
+## What Changes
+
+- Add CLI tool for declarative pacman package management
+- Support stdin input for package lists
+- Support multiple --state file inputs
+- Merge all inputs (additive strategy with empty state warning)
+- Force full upgrade of all packages (no partial upgrades)
+- Handle transitive dependencies automatically (users only specify direct packages)
+- Mark non-state packages as non-explicit before sync
+- After sync, remove orphaned packages (cleanup)
+- Support AUR packages: try pacman first, then makepkg, then report errors
+- Machine-readable output (install/remove counts, exit codes)
+- No conflict resolution for missing packages (append-only)
+- Print error to stderr for empty state input and exit with code 1
+
+## Capabilities
+
+### New Capabilities
+
+- **stdin-input**: Read package lists from standard input stream
+- **state-files**: Load declarative package states from files
+- **input-merging**: Combine multiple input sources (stdin + multiple --state files)
+- **state-validation**: Validate package names and empty states
+- **transitive-deps**: Automatically resolve all transitive dependencies
+- **pacman-sync**: Execute pacman operations to match declared state
+- **aur-sync**: Handle AUR packages: pacman first, then fall back to makepkg,
+                  then report errors
+- **machine-output**: Generate machine-readable sync results for scripting
+
+### Modified Capabilities
+
+None (new tool)
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/specs/aur-sync/spec.md b/openspec/changes/declpac-cli-tool/specs/aur-sync/spec.md
new file mode 100644
index 0000000..011ea1f
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/aur-sync/spec.md
@@ -0,0 +1,23 @@
+## ADDED Requirements
+
+### Requirement: Can handle AUR packages with pacman fallback
+
+The system SHALL attempt to install AUR packages by first trying pacman
+repositories, then falling back to AUR when pacman fails, and finally reporting
+errors for packages still missing.
+
+#### Scenario: Install from pacman first
+- **WHEN** package is in pacman repositories
+- **THEN** system shall install via pacman
+
+#### Scenario: Fall back to AUR
+- **WHEN** package is not in pacman repositories but is in AUR
+- **THEN** system shall attempt installation via makepkg (direct AUR build)
+
+#### Scenario: Report error for missing packages
+- **WHEN** package is not in pacman repositories or AUR
+- **THEN** system shall report error and print to stderr
+
+#### Scenario: Continue for remaining packages
+- **WHEN** some packages are installed and some fail
+- **THEN** system shall continue installation process for successful packages
diff --git a/openspec/changes/declpac-cli-tool/specs/input-merging/spec.md b/openspec/changes/declpac-cli-tool/specs/input-merging/spec.md
new file mode 100644
index 0000000..18f258d
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+++ b/openspec/changes/declpac-cli-tool/specs/input-merging/spec.md
@@ -0,0 +1,24 @@
+## ADDED Requirements
+
+### Requirement: Can merge multiple input sources
+
+The system SHALL combine package lists from all inputs using an additive
+strategy without conflict resolution.
+
+#### Scenario: Additive merging of all inputs
+- **WHEN** stdin and multiple state files provide package lists
+- **THEN** system shall include all packages from all inputs in the final state
+
+#### Scenario: Input priority is last-writer-wins per file
+- **WHEN** multiple state files contain the same package name
+- **THEN** the package from the last provided file in command-line order takes
+  precedence
+
+#### Scenario: Missing packages from stdin are added
+- **WHEN** stdin contains packages not in state files
+- **THEN** those packages shall be added to the final state
+
+#### Scenario: Duplicate packages accumulate
+- **WHEN** the same package appears in multiple inputs
+- **THEN** it shall be included multiple times in the final state (pacman
+  handles duplicates)
diff --git a/openspec/changes/declpac-cli-tool/specs/machine-output/spec.md b/openspec/changes/declpac-cli-tool/specs/machine-output/spec.md
new file mode 100644
index 0000000..f8627f2
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/machine-output/spec.md
@@ -0,0 +1,21 @@
+## ADDED Requirements
+
+### Requirement: Can generate machine-readable output
+
+The system SHALL produce output suitable for automated scripting.
+
+#### Scenario: Install/remove count output
+- **WHEN** sync completes successfully
+- **THEN** system shall output: "<installed_count> package(s) installed, <removed_count> package(s) removed"
+
+#### Scenario: Empty output format
+- **WHEN** no packages to sync
+- **THEN** system shall output nothing (or indicate no changes)
+
+#### Scenario: Error details in output
+- **WHEN** pacman operation fails
+- **THEN** system shall include error details in output (package names, pacman error messages)
+
+#### Scenario: Exit code for scripting
+- **WHEN** sync completes
+- **THEN** system shall return exit code 0 for success, non-zero for errors
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/specs/orphan-cleanup/spec.md b/openspec/changes/declpac-cli-tool/specs/orphan-cleanup/spec.md
new file mode 100644
index 0000000..9efaa1b
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/orphan-cleanup/spec.md
@@ -0,0 +1,29 @@
+## ADDED Requirements
+
+### Requirement: Can mark non-state packages as non-explicit
+
+The system SHALL mark all packages not declared in the state as non-explicit
+(dependencies) before syncing, so they can be safely removed later.
+
+#### Scenario: Mark packages as non-explicit
+- **WHEN** packages are declared in state
+- **THEN** system shall mark those packages as explicitly installed via pacman -D --explicit
+- **AND** mark all other installed packages as non-explicit
+
+### Requirement: Can clean up orphaned packages
+
+After syncing, the system SHALL remove packages that are no longer required
+(as dependencies of removed packages).
+
+#### Scenario: Orphan cleanup after sync
+- **WHEN** sync operation completes successfully
+- **THEN** system shall run pacman -Rsu to remove unneeded dependencies
+- **AND** report the number of packages removed
+
+#### Scenario: Orphan cleanup respects explicitly installed
+- **WHEN** a package not in state is marked as explicitly installed by user
+- **THEN** system shall NOT remove it during orphan cleanup
+
+#### Scenario: No orphans to clean
+- **WHEN** there are no orphaned packages to remove
+- **THEN** system shall report "No packages to remove" in output
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/specs/pacman-sync/spec.md b/openspec/changes/declpac-cli-tool/specs/pacman-sync/spec.md
new file mode 100644
index 0000000..e95f804
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/pacman-sync/spec.md
@@ -0,0 +1,25 @@
+## ADDED Requirements
+
+### Requirement: Can sync system with declared package state
+
+The system SHALL execute pacman operations to install and upgrade all declared packages.
+
+#### Scenario: Full system upgrade with all packages
+- **WHEN** system has declared package list
+- **THEN** system shall run pacman -Syu with all declared package names
+
+#### Scenario: No partial upgrades
+- **WHEN** running pacman commands
+- **THEN** system shall use -Syu flag (full system upgrade) ensuring all packages are latest
+
+#### Scenario: Package availability check
+- **WHEN** a package from input is not in pacman repositories
+- **THEN** system shall report the error and include package name
+
+#### Scenario: Pacman execution capture
+- **WHEN** pacman commands execute
+- **THEN** system shall capture both stdout and stderr for error reporting
+
+#### Scenario: Exit code propagation
+- **WHEN** pacman commands execute
+- **THEN** system shall exit with code equal to pacman's exit code for success/failure detection
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/specs/state-files/spec.md b/openspec/changes/declpac-cli-tool/specs/state-files/spec.md
new file mode 100644
index 0000000..c2e454b
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/state-files/spec.md
@@ -0,0 +1,21 @@
+## ADDED Requirements
+
+### Requirement: Can load package states from state files
+
+The system SHALL load package lists from state files specified via --state flag.
+
+#### Scenario: Single state file loading
+- **WHEN** a state file is provided via --state flag
+- **THEN** system shall read package names from the file content
+
+#### Scenario: Multiple state file loading
+- **WHEN** multiple --state flags are provided
+- **THEN** system shall load package names from each file
+
+#### Scenario: State file format is text list
+- **WHEN** loading from state files
+- **THEN** system shall parse whitespace-delimited package names
+
+#### Scenario: File path validation
+- **WHEN** a state file path points to a non-existent file
+- **THEN** system shall report a file read error
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/specs/state-validation/spec.md b/openspec/changes/declpac-cli-tool/specs/state-validation/spec.md
new file mode 100644
index 0000000..9017fef
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+++ b/openspec/changes/declpac-cli-tool/specs/state-validation/spec.md
@@ -0,0 +1,17 @@
+## ADDED Requirements
+
+### Requirement: Can detect empty state input
+
+The system SHALL detect when no packages are provided in any input source.
+
+#### Scenario: Empty state warning
+- **WHEN** no package names are found in stdin or state files
+- **THEN** system shall print a warning to stderr
+
+#### Scenario: Empty state warning message
+- **WHEN** warning is printed for empty state
+- **THEN** message shall say: "Called without state, aborting.."
+
+#### Scenario: Abort on empty state
+- **WHEN** empty state is detected
+- **THEN** system shall exit with code 1 (error: no packages to sync)
diff --git a/openspec/changes/declpac-cli-tool/specs/stdin-input/spec.md b/openspec/changes/declpac-cli-tool/specs/stdin-input/spec.md
new file mode 100644
index 0000000..3ff2c54
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/stdin-input/spec.md
@@ -0,0 +1,17 @@
+## ADDED Requirements
+
+### Requirement: Can read package lists from stdin
+
+The system SHALL accept package names from standard input, where each line represents a package name.
+
+#### Scenario: Packages from stdin are read correctly
+- **WHEN** package names are passed via stdin separated by whitespace, tabs, or newlines
+- **THEN** system shall parse each unique package name from the input stream
+
+#### Scenario: Empty stdin input is handled
+- **WHEN** stdin contains no package names
+- **THEN** system shall skip stdin input processing
+
+#### Scenario: Whitespace normalization
+- **WHEN** packages are separated by multiple spaces, tabs, or newlines
+- **THEN** each package name shall have leading/trailing whitespace trimmed
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/specs/transitive-deps/spec.md b/openspec/changes/declpac-cli-tool/specs/transitive-deps/spec.md
new file mode 100644
index 0000000..cdfc153
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/specs/transitive-deps/spec.md
@@ -0,0 +1,23 @@
+## ADDED Requirements
+
+### Requirement: Can resolve transitive dependencies automatically
+
+The system SHALL automatically determine and install all transitive dependencies
+for declared packages, so users only need to specify direct packages.
+
+#### Scenario: Transitive dependencies are resolved
+- **WHEN** a package with dependencies is declared in state
+- **THEN** system shall identify all transitive dependencies via pacman
+- **AND** include them in the installation operation
+
+#### Scenario: Dependency resolution includes AUR dependencies
+- **WHEN** a package's transitive dependencies include AUR packages
+- **THEN** system shall resolve those AUR dependencies via makepkg
+
+#### Scenario: Shared dependencies are deduplicated
+- **WHEN** multiple declared packages share dependencies
+- **THEN** system shall install each shared dependency only once
+
+#### Scenario: Missing dependency handling
+- **WHEN** a declared package has a dependency not available in pacman or AUR
+- **THEN** system shall report error for the missing dependency
\ No newline at end of file
diff --git a/openspec/changes/declpac-cli-tool/tasks.md b/openspec/changes/declpac-cli-tool/tasks.md
new file mode 100644
index 0000000..ae728e9
--- /dev/null
+++ b/openspec/changes/declpac-cli-tool/tasks.md
@@ -0,0 +1,81 @@
+## 1. Project Setup
+
+- [ ] 1.1 Initialize Go module with proper imports
+- [ ] 1.2 Add required dependencies (libalpm wrapper)
+- [ ] 1.3 Set up project structure (main.go, pkg/ subdirectory)
+
+## 2. Input Parsing
+
+- [ ] 2.1 Implement stdin reader to collect package names
+- [ ] 2.2 Implement state file reader for text-list format
+- [ ] 2.3 Add whitespace normalization for package names
+- [ ] 2.4 Create package name set data structure
+
+## 3. Input Merging
+
+- [ ] 3.1 Implement additive merging of stdin and state file packages
+- [ ] 3.2 Handle multiple --state flags with last-writer-wins per file
+- [ ] 3.3 Implement duplicate package handling (no deduplication)
+
+## 4. State Validation
+
+- [ ] 4.1 Implement empty state detection (no packages found)
+- [ ] 4.2 Add stderr error output for empty state
+- [ ] 4.3 Set exit code 1 for empty state case (abort, not proceed)
+
+## 5. Pacman Integration
+
+- [ ] 5.1 Implement pacman -Syu command execution wrapper
+- [ ] 5.2 Add command-line argument construction with package list
+- [ ] 5.3 Capture pacman stdout and stderr output
+- [ ] 5.4 Implement pacman error message parsing
+- [ ] 5.5 Handle pacman exit codes for success/failure detection
+- [ ] 5.6 Verify pacman automatically resolves transitive dependencies
+- [ ] 5.7 Verify shared dependencies are deduplicated by pacman
+
+## 6. Explicit Marking & Orphan Cleanup
+
+- [ ] 6.1 Get list of currently installed packages before sync
+- [ ] 6.2 Mark declared state packages as explicitly installed via pacman -D --explicit
+- [ ] 6.3 Run pacman sync operation (5.x series)
+- [ ] 6.4 Run pacman -Rsu to remove orphaned packages
+- [ ] 6.5 Capture and report number of packages removed
+- [ ] 6.6 Handle case where no orphans exist (no packages removed)
+
+## 7. AUR Integration
+
+- [ ] 7.1 Implement AUR package lookup via package query (Jguer/aur)
+- [ ] 7.2 Add pacman first attempt (package not in repos)
+- [ ] 7.3 Implement AUR fallback using makepkg (direct build, not AUR helper)
+- [ ] 7.4 Clone AUR package git repo to temp directory
+- [ ] 7.5 Run makepkg -si in temp directory for installation
+- [ ] 7.6 Add stderr error reporting for packages not in pacman or AUR
+- [ ] 7.7 Capture makepkg stdout and stderr for output parsing
+- [ ] 7.8 Handle makepkg exit codes for success/failure detection
+
+## 8. Output Generation
+
+- [ ] 8.1 Capture installed/removed package counts from pacman output
+- [ ] 8.2 Generate machine-readable output line in requested format
+- [ ] 8.3 Include error details in output on failure
+
+## 9. CLI Interface
+
+- [ ] 9.1 Implement --state flag argument parsing
+- [ ] 9.2 Implement stdin input handling from /dev/stdin
+- [ ] 9.3 Set up correct CLI usage/help message
+- [ ] 9.4 Implement flag order validation
+
+## 10. Integration & Testing
+
+- [ ] 10.1 Wire together stdin -> state files -> merging -> validation -> pacman sync -> orphan cleanup -> output
+- [ ] 10.2 Test empty state error output and exit code 1
+- [ ] 10.3 Test single state file parsing
+- [ ] 10.4 Test multiple state file merging
+- [ ] 10.5 Test stdin input parsing
+- [ ] 10.6 Test explicit marking before sync
+- [ ] 10.7 Test pacman command execution with real packages
+- [ ] 10.8 Test orphan cleanup removes unneeded packages
+- [ ] 10.9 Test AUR fallback with makepkg for AUR package
+- [ ] 10.10 Test error handling for missing packages
+- [ ] 10.11 Generate final binary
diff --git a/openspec/config.yaml b/openspec/config.yaml
index b118dd0..c614a6e 100644
--- a/openspec/config.yaml
+++ b/openspec/config.yaml
@@ -1,7 +1,18 @@
+---
+
 schema: spec-driven
 
 context: |
-  Tech stack: Go
+  - Tech stack: Go
+  - Minimal external dependencies
+  - Use Jguer/dyalpm for interfacing with libalpm
+  - Use Jguer/aur for interfacing with the AUR API
+
+rules:
+  style-guide: |
+    - Favor creating and using helper library functions over local on-offs
+    - When writing non-code documents, strictly adhere to the 80 character line
+      limit
 
 # Project context (optional)
 # This is shown to AI when creating artifacts.