Human translation API for AI agents, no account needed
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Tracked since2026
0 reviews trackedThe Bottom Line
Entry price
Paid plans only
Biggest pro
Zero pre-registration and no API key needed for agents to start translating
Biggest con
Payment flow currently supports US-issued cards only
TL;DR - Nitro 4.0
- AI agents can autonomously call the API without any account or API key, using a 402 Payment Required challenge and MPP payment flow.
- Translations are done by professional native-speaker translators in 80+ languages, with support for complex formats and domain-specific expertise.
- The service provides cultural fluency, accountability with QA and revisions, and a 2-24 hour turnaround for production workflows.
Pricing: Paid only
Best for: Enterprises & pros
What is Nitro 4.0?
Nitro is a human translation API designed specifically for AI agents. It allows agents to autonomously submit translation requests without any prior account creation or API key management. The API uses a unique payment flow where the agent receives a 402 Payment Required challenge, obtains a payment token from an MPP-compatible provider, and retries the request with the payment credential. Translations are performed by professional native-speaker translators in over 80 languages, with support for complex formats like HTML, JSON, and XML. The service offers cultural fluency, domain expertise, and built-in QA and revisions, making it suitable for legal, medical, financial, and marketing content. Average turnaround is 2-24 hours, and the agent polls for completion.
Pros & Cons
Pros
- Zero pre-registration and no API key needed for agents to start translating
- Human-quality translations with cultural fluency and domain expertise
- Supports complex markup formats without breaking structure
Cons
- Payment flow currently supports US-issued cards only
- Not instant; average turnaround is 2-24 hours
Key Features
No API key or account creation required for agent-callable translationSupports 80+ languages with professional native-speaker translatorsHandles complex formats: HTML, JSON, XML, iOS stringsBuilt-in QA and revisions for accuracy and accountabilityDomain expertise for legal, medical, financial, and gaming contentAutonomous agent flow with 402 Payment Required challenge and MPP paymentPolling-based order status (QUEUE, IN_PROGRESS, DONE) with ~10 second intervalsEndpoints for rate checking, price estimation, order submission, and order retrieval
Pricing
Paid
Nitro 4.0 offers paid plans. Visit their website for current pricing details.
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Nitro 4.0 FAQ
How does the 402 Payment Required flow work for AI agents?
The agent sends a POST /translate request without authentication and receives a 402 response with a WWW-Authenticate header containing a payment challenge. The agent then obtains a payment token from any MPP-compatible provider, builds a base64url credential, and retries the exact same request body (byte-for-byte identical) with an Authorization: Payment <credential> header. On success, it gets a 200 OK with a Payment-Receipt and order details.
What types of content formats does Nitro support for translation?
Nitro supports HTML, JSON, XML, and iOS strings formats. The translators preserve the markup and structure while translating only the content, ensuring no broken tags or corrupted keys.
Can I use Nitro with a traditional API key instead of the payment credential?
Yes, Nitro works both ways. You can use an API key for authentication, or you can use the payment credential from the MPP flow. The POST /translate, GET /orders/{id}, and GET /orders endpoints accept either a payment credential or an API key.
How does Nitro ensure translation quality for specialized domains like legal or medical content?
Nitro uses professional native-speaker translators with domain expertise in legal, medical, financial, and gaming content. Every translation comes with built-in QA and revisions, and the service provides accountability for accuracy, which is critical for legal liability, brand reputation, and compliance.
What is the typical turnaround time for a translation order?
The average turnaround time is 2-24 hours. The agent places the order, polls for status every ~10 seconds, and picks up the result when the status changes to DONE.
Can I estimate the cost of a translation before placing an order?
Yes, Nitro provides a POST /calculate endpoint that allows you to estimate the price before placing an order. There is also a GET /rates endpoint to check current rates per 1,000 characters for any language pair.
What happens if the retry request body is not identical to the original?
The server checks the SHA-256 hash of the request body. If the retry body is not byte-for-byte identical to the original, the request will fail. The agent must ensure the exact same body is sent in the retry.
Is the payment credential reusable for multiple requests?
Yes, you need to save the payment credential because it is required for subsequent GET /orders/{id} and GET /orders calls to check status and retrieve translated text.
Source: nitrotranslate.com