Lemon and Speaky Box start from the same idea: your voice makes a better prompt than your keyboard. Here's how the two differ in practice, as of September 2026.
The same Smart key in Mail writes an email, not a prompt. Speaky Box reads which app is in front and changes what it writes.
Both are built around the voice-to-prompt idea: ramble at Claude or ChatGPT and get a structured prompt instead of a transcript. Both also do plain dictation in every other app. Both are hold-to-talk, both are quick to set up, and both are a lot better than typing prompts by hand.
Lemon has a prompt mode for AI tools and a dictation mode for everything else. Speaky Box goes one step further: the Smart key writes for whichever app is in front. A prompt in Claude, an email with a greeting and sign-off in Mail, a short casual message in Slack. You don't switch modes; it reads the window title.
Lemon uses the function key. Speaky Box lets you pick any key for each of its two jobs, and you can turn either off. If you only want the AI prompting, run Smart alone. If you only want plain dictation, run Dictate alone. Caps lock, fn, right option, whatever you don't use.
Speaky Box has a Words page where you add names and terms once, and a Context page where you describe your work in a few lines. Both keys use them, so your product name is spelt right in a Slack message and your customer's name is right in a prompt. Lemon learns from use over time.
Lemon runs on Mac and Windows. Speaky Box is Mac only. Speaky Box is free for 2,000 words a week and £8.99 a month for unlimited; Lemon is free to start with pricing on their site. If you need Windows, Lemon is the answer.
you're on Windows, or you want the product with the longer track record on voice-to-prompt.
you want one app that's as good in Mail and Slack as it is in Claude, two keys you control, a plain free tier, and your history staying on your Mac.