Test & Score Your Email Subject Lines Score and optimize email subject lines for open rates with actionable suggestions.

The Email Subject Line Tester uses a combination of string manipulation and regular expressions to analyze the input subject line. It splits the subject into words using the `\s+` pattern and counts the number of words to determine if it falls within the ideal range of 4-9 words. The tool also checks for power words by iterating over an array of predefined power words and using the `some()` method to check if any of these words are present in the subject line. To detect spam triggers, it uses a similar approach with an array of known spam phrases and checks if any of these phrases are present in the subject line using the `includes()` method. The scoring algorithm is implemented using a simple additive model, where each factor contributes a fixed score to the overall total, which is then clamped to a range of 0-100 using the `Math.max()` and `Math.min()` functions.

The tool uses React's `useState` hook to store the input subject line in the component's state, and the `analyze()` function is called whenever the state changes. The result of the analysis is stored in an object with properties for the score, label, color, and tips, which are then used to render the UI components. The tool also uses SVG elements to display a circular progress bar representing the subject line's score, with the `strokeDasharray` and `strokeDashoffset` attributes used to animate the circle. To ensure proper rendering on different devices, it checks the subject line length against mobile preview constraints of 35 characters and desktop preview constraints of 60 characters, using these values to determine whether to display a checkmark or warning symbol in the UI.

The code uses TypeScript to define interfaces for the score result object, which includes properties for the score, label, color, and tips. It also uses JavaScript's built-in `Array.prototype` methods such as `some()` and `filter()` to iterate over arrays and perform conditional checks. The regular expressions used in the tool are defined using JavaScript's RegExp syntax, with patterns such as `\d` to match digits and `[!?]{2,}` to match excessive punctuation. Overall, the Email Subject Line Tester uses a combination of string manipulation, regular expressions, and React components to provide a user-friendly interface for analyzing and improving email subject lines.