What an API key is
An API key is a long password that connects Rectoly to an AI company. You sign up with the company in your own name, and the company issues the key.
- Rectoly has no contract with any AI company. With your key, Rectoly asks the company to do the work in your name, and the company bills you.
- What goes to the company is the paragraphs you translate and the text of the notes you organize. Your paper files are not sent. See What is sent.
- You do not need a key to use AI on This device. A key is for a device that cannot run the model, or for when you would rather use a company's model. See Choose where AI runs.
- A ChatGPT or Gemini app subscription is separate from the API. It gives you no API key and no API credit.
- In some regions and stores, Settings has no AI. A key cannot be used there.
In Rectoly, Get a key opens the key page of the AI company you chose. The steps for each company are below: OpenAI, Google Gemini, DeepSeek.
What it costs
The app's screens give an estimate of how much text is sent, never a price. This page is the only place where Rectoly gives amounts of money, and they are rough.
- The companies count text in tokens, small pieces of words. Translating a whole paper sends and receives about 20,000 to 40,000 tokens.
- With the models below, translating a whole paper costs a few US cents at most. Organize with AI and paper cards use far less.
| AI company | Model | Sent, per 1M tokens | Returned, per 1M tokens | One paper translated |
|---|---|---|---|---|
| OpenAI | gpt-4.1-mini | $0.40 | $1.60 | about $0.02–0.04 |
| Google Gemini | gemini-2.5-flash-lite | $0.10 | $0.40 | about $0.01 or less |
| DeepSeek | deepseek-flash | $0.30 (2 yuan) | $1.20 (8 yuan) | about $0.01–0.03 (0.1–0.2 yuan) |
- These are the prices on each company's pricing page on 2026-10-16. Prices change, and the company's page is the authority: OpenAI, Google Gemini, DeepSeek.
- DeepSeek's prices are for its peak hours (weekday working hours in Beijing). At other times they are half.
Paying in advance. OpenAI and DeepSeek work on prepaid credit: you put money in first, and each request is paid from it. When it runs out, the company stops taking requests, so you spend about what you put in and no more. OpenAI's smallest top-up is $5, and its credit expires after a year.
Free of charge. Google Gemini has a free tier: a key from Google AI Studio works without payment, with a limit on how many requests you make per minute and per day. On the free tier, Google may use what you send to improve its products. For a manuscript under review or anything confidential, set up billing first.
Keeping spending in check.
- OpenAI: when you add credit, turn off automatic top-up (auto recharge). Settings › Limits on platform.openai.com can email you when spending reaches an amount you set.
- Google Gemini: in Google AI Studio, Spend › Monthly spend cap sets a monthly cap for a project with billing.
- DeepSeek: nothing is charged automatically. The balance you top up is the limit.
OpenAI
These steps show the screens as of 2026-10-16. The company may change them.
1. Create an account
Open platform.openai.com and sign up with an email address or a Google, Microsoft or Apple account. You may be asked to confirm a phone number. A ChatGPT account works here too.
2. Add credit
In Settings › Billing, press Add payment details and add credit ($5 or more). Turn off auto recharge unless you want it topped up automatically. Without credit, the key does not work.
3. Open the API keys page
Open platform.openai.com/api-keys and press Create new secret key. In Rectoly, Get a key opens this page.
4. Name the key and create it
Type a name you will recognize, such as "Rectoly", and press Create secret key. Leave the other choices as they are.
5. Copy the key
Press Copy. The key starts with sk-. Once you close this window, the key is never shown again. If you lose it, delete it and create a new one.
6. Paste it into Rectoly
In Rectoly, open Settings › AI and choose Your own API key under Where AI runs (the first time, read the notice and agree). Choose OpenAI as the AI company and press Paste and check. When it reads In use:, translation, Organize with AI and paper cards run with OpenAI. More: Set up your own API key.
A video of these steps is in preparation.
Google Gemini
These steps show the screens as of 2026-10-16. The company may change them.
1. Open Google AI Studio
Open aistudio.google.com/apikey and sign in with your Google account. The first time, agree to the terms. A school or work account may not be allowed to use it; then use a personal account. In Rectoly, Get a key opens this page.
2. Create a key
Press Create API key.
3. Choose a project
Choose the project the key belongs to and create the key. A new account already has a project; choose that one.
4. Copy the key
Copy the key that appears. It starts with AQ., not AIza as Gemini keys used to.
5. Paste it into Rectoly
In Rectoly, open Settings › AI and choose Your own API key under Where AI runs (the first time, read the notice and agree). Choose Google Gemini as the AI company and press Paste and check. When it reads In use:, translation, Organize with AI and paper cards run with Gemini. More: Set up your own API key.
- The key starts on the free tier. To go past its limits, press Set up billing in Google AI Studio. See What it costs.
A video of these steps is in preparation.
DeepSeek
These steps show the screens as of 2026-10-16. The company may change them.
1. Sign up
Open platform.deepseek.com and sign up with a phone number or an email address.
2. Top up first
Open Top up and pay in advance. DeepSeek takes no requests without a balance. The ways to pay depend on your region.
3. Open API keys
Open API keys and press Create new API key. In Rectoly, Get a key opens this page.
4. Name the key and copy it
Type a name such as "Rectoly", create the key, and copy it. The key starts with sk- and is shown only once.
5. Paste it into Rectoly
In Rectoly, open Settings › AI and choose Your own API key under Where AI runs (the first time, read the notice and agree). Choose DeepSeek as the AI company and press Paste and check. When it reads In use:, translation, Organize with AI and paper cards run with DeepSeek. More: Set up your own API key.
A video of these steps is in preparation.
Keeping the key safe
Anyone who has your key can use the company's AI at your expense.
- Do not show it to anyone. Keep it out of screenshots, chats and shared documents.
- Do not send it to anyone, Rectoly's support included. We never ask for it.
- If it may have leaked, delete it on the company's key page and create a new one, then paste the new key into Rectoly.
- Rectoly keeps the key on this device only: in the Keychain on iPad, iPhone and Mac, encrypted with a key held in the device's secure hardware on Android, encrypted for your Windows user on Windows, and encrypted in a file only your user can read on Linux.
- The key is not synced to your other devices. Paste it on each device, or give each device a key of its own, so you can delete one without the others.
When something goes wrong
| What Rectoly says | What it means | What to do |
|---|---|---|
| The API key was not accepted. | The key is wrong, cut short or deleted | Copy the key again on the company's page and press Paste and check. Check that the AI company is the one that issued the key |
The API key was not accepted. for a Gemini key that starts with AQ. | Since late May 2026, Google has been moving to a new kind of key (AQ.), and AI Studio no longer makes the old kind (AIza). Rectoly accepts the new kind, so the refusal comes from Google, part-way through its move | Wait and try again later. Some users report on the Google AI Developers Forum that a key made for the Gemini API in the Google Cloud console works |
| This is not the shape of a (company) key. | You pasted a key from another company, or something that is not a key | Choose the AI company that issued the key, or copy the key again |
| …rate limit was reached… | Too many requests in a short time, or no prepaid credit left (OpenAI says this when the credit runs out) | Wait a little. If it keeps happening, add credit on the company's page. Gemini's free tier resets its daily limit the next day |
| …rejected the request: followed by the company's message | The company gave its own reason. Insufficient Balance means the prepaid credit is used up; a message about the model means that model is not available | Top up, or choose another model under Advanced |
| …is not responding… | The company's service is busy or down | Wait and try again. Each company's status page says whether it has a problem: OpenAI, Google Gemini, DeepSeek |
| Could not connect. | This device is not online, or the network blocks the company | Check the connection. A school or office network may block the company |