Terms of Service

The Extension reads text aloud. You can:

• Read a Google Docs document — the selected text or the whole document.
• Read ordinary web pages and articles, and PDF files you open in the Extension’s viewer.
• Follow along: the sentence and the word being read are highlighted in sync.
• Choose a voice and adjust the reading speed.

Some features depend on our servers: preparing text for correct pronunciation, delivering downloadable voice models, server voices when we offer them, and the list of available voices. We may change, limit, suspend or withdraw any feature, including server-side features, at any time and, where the law allows, without notice; where the law requires it, we will give you notice of material changes or of discontinuation. We may apply usage limits to keep the service available for everyone. When server-side features are unavailable, the Extension tries to keep reading with the voices available on your device; uninterrupted playback is not guaranteed.

The Extension is free to use. There are no paid plans, subscriptions or in-app purchases. No account or sign-in is required. If we ever add optional paid features, nothing will be charged without your clear agreement, and we will update these Terms first.

You must be at least 13 years old to use the Extension. If you are under 18, use it with the permission of a parent, guardian or school.

System voices are the voices installed on your device and the voices Chrome provides. Which of them are available, and how they sound, depends on your operating system and browser, which are outside our control. Some Chrome voices are cloud voices provided by Google and are subject to Google’s own terms and privacy policy.

Natural voices are marked “Natural” in the voice list. To use a natural voice, you choose it and press Download: the voice model is then downloaded to your browser, and speech with this voice is generated there. Natural voices need a reasonably recent computer; if a natural voice cannot run on your computer, or runs too slowly, the Extension reads with another voice. We may add, change or remove natural voices at any time. Some natural voices are subject to the model license terms set out in the next section.

Server voices are generated on our server. Whether any server voices are offered, and which ones, is decided by us and may change without an update to the Extension.

What happens to the text you listen to, including when it is sent to our server, is described in our Privacy Policy.

Some “Natural” voices in the Extension are produced by Supertonic 3, a text-to-speech model created by Supertone Inc. These are the voices whose card says that the voice is distributed under the Open RAIL-M license (at the time of writing: Leo, Max, Mia and Ella). When you press Download on such a card, the model files are downloaded to your browser, and the speech is then generated on your device.

Supertonic 3: Copyright (c) 2026 Supertone Inc. The model is licensed under the BigScience Open RAIL-M License dated August 18, 2022 (the “License”). The full text of the License is available at astelle.app/licenses/supertonic-3.txt; a copy is also included in the Extension and stored next to the model files on our server. We are not affiliated with, sponsored or endorsed by Supertone Inc.

Your agreement. By downloading or using a Supertonic voice, you agree to comply with paragraph 5 of the License, including the use restrictions set out in its Attachment A. These restrictions are part of these Terms and are binding on you. In the words of the License:

You agree not to use the Model or Derivatives of the Model:

• (a) In any way that violates any applicable national, federal, state, local or international law or regulation;
• (b) For the purpose of exploiting, harming or attempting to exploit or harm minors in any way;
• (c) To generate or disseminate verifiably false information and/or content with the purpose of harming others;
• (d) To generate or disseminate personal identifiable information that can be used to harm an individual;
• (e) To generate or disseminate information and/or content (e.g. images, code, posts, articles), and place the information and/or content in any context (e.g. bot generating tweets) without expressly and intelligibly disclaiming that the information and/or content is machine generated;
• (f) To defame, disparage or otherwise harass others;
• (g) To impersonate or attempt to impersonate (e.g. deepfakes) others without their consent;
• (h) For fully automated decision making that adversely impacts an individual’s legal rights or otherwise creates or modifies a binding, enforceable obligation;
• (i) For any use intended to or which has the effect of discriminating against or harming individuals or groups based on online or offline social behavior or known or predicted personal or personality characteristics;
• (j) To exploit any of the vulnerabilities of a specific group of persons based on their age, social, physical or mental characteristics, in order to materially distort the behavior of a person pertaining to that group in a manner that causes or is likely to cause that person or another person physical or psychological harm;
• (k) For any use intended to or which has the effect of discriminating against individuals or groups based on legally protected characteristics or categories;
• (l) To provide medical advice and medical results interpretation;
• (m) To generate or disseminate information for the purpose to be used for administration of justice, law enforcement, immigration or asylum processes, such as predicting an individual will commit fraud/crime commitment (e.g. by text profiling, drawing causal relationships between assertions made in documents, indiscriminate and arbitrarily-targeted use).

Mark published audio as machine-generated. If you publish or share audio created with a Supertonic voice, for example in a video, a podcast, a post or on a website, you must expressly and intelligibly state that the audio is machine-generated (synthetic speech). This is required by item (e) above.

Your responsibility for the output. You are responsible for the audio you generate with a Supertonic voice and for how you use it.

Copies of the model. If you copy or redistribute the Supertonic model files, you may do so only under the License: give every recipient a copy of the License and pass these use restrictions on to them.

Availability. We may disable or remove the Supertonic voices at any time, for example to comply with the License. If we do, the Extension keeps reading with other voices.

You agree NOT to:

• Use the Extension to read or process content you do not have the right to access, or in a way that infringes the rights of others.
• Use the Extension, our server or the voice models for anything other than listening to text through the Extension — for example, for bulk or automated text processing or speech generation, or to build another product or dataset on top of our server.
• Access our server other than through the Extension, probe or overload it, or try to get around usage limits.
• Attempt to reverse-engineer, decompile or tamper with the Extension, except where the law allows it.
• Use automated tools, bots or scripts to access the Extension in ways not intended by us.
• Resell, sublicense or redistribute the Extension without our written permission.
• Use the Extension to break the law, to distribute malware or to harm others.
• Use audio created with the Extension to deceive, impersonate or defame anyone; for Supertonic voices, the restrictions above also apply.

We may stop providing the Extension to you, or restrict access to our server, if you breach these rules.

Nothing in Sections 4 and 5 limits the rights that a third-party licence grants you for a component, such as the Supertonic model licence; if these Terms and such a licence conflict for that component, the licence prevails.

The Extension, its code, design and branding are owned by us and protected by intellectual-property laws, except for third-party components, which are provided under their own licenses; copies of those licenses are included in the Extension. These Terms grant you a personal, non-exclusive, non-transferable, revocable licence to use the Extension for its intended purpose. We grant you no other rights.

The text and documents you choose to read remain yours; we claim no ownership over them, and we do not store them (see our Privacy Policy).

If you send us ideas, suggestions or feedback, we may use them freely to improve the Extension, without any obligation to you.

The Extension is provided “as is” and “as available”, without warranties of any kind, whether express or implied, including fitness for a particular purpose, accuracy of speech output or uninterrupted availability. Speech output is machine-generated and may contain mistakes, including mispronounced words, numbers or names; do not rely on it where accuracy matters, such as for medical, legal or financial content, without checking the original text. Voice quality and availability depend on your device, your browser and, for server-side features, on our servers and your connection. The Extension is not a certified accessibility aid and does not replace professional assistive technology or services. We are not responsible for the content of the documents and websites you choose to read.

To the fullest extent permitted by law, we will not be liable for any indirect, incidental, special or consequential damages, or for loss of data, profits or business, arising from your use of or inability to use the Extension or the Website. Because the Extension is provided free of charge, our total liability for any claim relating to it is limited to the amount you paid for it, which is zero, except where you are a consumer and the law of your country does not allow such a limit. Nothing in these Terms excludes or limits our liability for fraud, wilful misconduct, death or personal injury caused by our negligence, or any other liability that applicable law does not allow us to exclude or limit.

You are responsible for how you use the Extension and for any audio you create with it. If you use the Extension for business purposes, or if you use it unlawfully or in material breach of these Terms or of the Supertonic license restrictions, and a third party brings a claim against us because of that use, you will reimburse our reasonable, documented losses and costs directly caused by that claim, to the extent permitted by law. This does not cover losses caused by us, and we will not settle such a claim at your expense without your reasonable consent.

We may update the Extension and these Terms from time to time. When we change these Terms, we will update the “Last updated” date at the top; if the change is significant, we will also tell you in the Extension or on the Website. Continued use of the Extension after a change means you accept the updated Terms. We may also discontinue the Extension or any of its features at any time.

Nothing in these Terms removes or limits any statutory rights you have as a consumer under the law of your country of residence that cannot be waived by agreement.