# Spec: Weather Fetcher CLI

**Objective**: A Python CLI tool that fetches current weather for a city using a public API.

## User Stories

### US1: Fetch current weather [P1]
As a CLI user, I want to fetch the current temperature and description for a city.
- **Input**: City name (string).
- **Output**: JSON or formatted table with "Temperature (C)" and "Condition".

### US2: API Key Management [P1]
As an administrator, I want the tool to read the API key from an environment variable `WEATHER_API_KEY`.
- **Validation**: Fail with a clear error if the variable is missing.

### US3: Units selection [P2]
As a international user, I want to choose between Metric (Celsius) and Imperial (Fahrenheit) via a flag.
- **Acceptance Criteria**: `--units metric` or `--units imperial`.

## Non-Functional Requirements
- **Performance**: Response within 2 seconds.
- **Reliability**: Handle invalid city names gracefully.

## Success Criteria
- [ ] Tool returns weather for "Worms, DE".
- [ ] Tool fails gracefully for "NonExistentCity".
- [ ] All tests pass with 80% coverage.