An API key is a credential that authenticates a request to somebody else's server and, usually, bills you for making it. Whether a transcription tool needs one comes down to a single question: does the actual work — turning audio into text, or text into a summary — happen on a machine you control, or on one you're calling over the network. If it's the second, an API key is how that call gets authorised and metered; if it's the first, there's no call to authorise.
Where a key shows up in practice
Two common setups need one. A tool built as a thin interface over a cloud transcription or language-model service asks for your own key to that service so it can bill your account rather than the tool-maker's. And a homemade pipeline — a script that transcribes locally but calls a cloud service for the summarising step — needs a key for that second half even if the first half runs entirely offline. Coii AudioNotes against a Whisper CLI script covers a version of that second case: the transcription engine itself is free and local, but turning its output into minutes with an external model is a separate piece someone has to wire in, key included.
What the key actually protects the vendor from
From the vendor's side, an API key exists to meter usage and stop an unauthenticated request from running up a bill on somebody else's account — it's not primarily a security feature for the person using the tool, even though it's often described as one. For the person holding the key, it means one more credential to keep out of a committed file, one more thing that can expire or get rate-limited, and a running cost tied to how much gets transcribed.
What runs with no key at all
A tool where the model doing the work ships inside the app itself has nothing to authenticate, because there's no second machine being asked to do anything. Coii AudioNotes is built that way: the language model that writes the summary is bundled with the app, and transcription runs on your Mac as the meeting happens, so there's no account to create and no key to generate, copy, or rotate when it expires. What is local transcription covers what "runs on your own machine" means in more detail, beyond just the absence of a key.
What to check before signing up for one
If a tool does ask for a key, it's worth reading the pricing page behind that key before typing anything in: usage-based billing means the monthly number you were quoted for the app itself can be the smaller part of what you actually pay once real usage starts, especially for anyone transcribing several hours of audio a week rather than the odd short call.
Why this is worth checking before buying
A tool's price alone doesn't tell you whether a per-use cost is hiding behind it — an app that's free or cheap up front but calls a metered API underneath can cost more over a year of regular use than one priced higher with everything included. Local transcription apps for Mac rounds up tools built the way Coii AudioNotes is, where the price on the box is the whole cost, with nothing metered running in the background.