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What is an API license: an agreement in which the provider of an API grants another party the right to use that API, under clear conditions regarding usage rights, rate limits, liability, intellectual property, data processing, and payment. In short: the contract that regulates who may use your integration, how intensively, and what happens if something goes wrong. For software companies that make an API publicly available, this is the legal backbone of the product.
The short answer
- Right of use: which API endpoints the consumer may call and for what purpose.
- Rate limits / fair use: how many calls are allowed per period.
- Availability and liability: the uptime you promise and for which you are liable.
- Intellectual property: the API and documentation remain the property of the provider.
- Data and GDPR: who is the controller and who is the processor.
- Payment and cancellation: price per call or subscription, and when access is terminated.
What exactly does an API license regulate?
An API (Application Programming Interface) is the link through which other software calls your service. As soon as you make it available to third parties—customers, partners, or developers—you need a contract that defines the usage. Without a license, it is unclear what the recipient is permitted to do, what you guarantee, and who is liable in the event of malfunctions or misuse.
The API license differs from standard software: the customer does not receive a copy of your code, but access to a running service. This makes provisions regarding availability, rate limits, and data processing more important than with a classic software license.
Usage rights and rate limits
The right of use defines the core: which endpoints the customer may call, for what purpose, and with how many users. Usually, the right is non-exclusive, non-transferable, and limited to own use — resale or the development of a competing service is excluded.
- Rate limits: a hard limit, for example 1,000 calls per minute. Exceeding this results in error messages (HTTP 429).
- Fair use: a softer standard that counters excessive or unreasonable use without an exact figure.
- Sanctions: in the event of persistent overshooting, you may throttle, charge extra, or suspend access.
Always stipulate that you may adjust rate limits with reasonable notice. Without that freedom, you are bound by the initial estimate.
Availability and liability
Customers rely on your API and want assurance regarding uptime. Do not promise anything you cannot deliver. Common practice is a best-efforts obligation or an SLA with a percentage (for example, 99.5%), with clear exceptions for maintenance and force majeure.
You link liability to this. Limit your liability to direct damage, exclude consequential damage (lost revenue, data loss), and set a maximum — often the compensation for the last 6 or 12 months. Without this limitation, a single outage at a major customer can far exceed your revenue.
Intellectual property
The API, the documentation, the underlying software, and the trademark remain the property of the provider. The purchaser acquires only a right of use, not any transfer. Also stipulate that the purchaser may not reverse-engineer or decompile the API.
Pay attention to the data flowing through the API. Content provided by the recipient generally remains the property of the recipient; results generated by your service may belong to you. Make this distinction explicit, otherwise disputes will arise regarding who is allowed to reuse what.
Data and GDPR
If the API processes personal data, the GDPR applies. Determine who is the controller and who is the processor. If you process data on behalf of the customer, a data processing agreement is required with agreements regarding security, sub-processors, transfers outside the EU, and the obligation to report data breaches.
An SME example: a SaaS company offers an address validation API. Customers submit address details; the SaaS company processes these on behalf of the customer. Without a Data Processing Agreement and clear retention periods, the SaaS company faces a GDPR risk that is separate from the commercial agreements.
Payment and withdrawal
Payment can be made in various ways: a fixed subscription, a price per call (pay-per-use), or a combination of a base fee plus usage. Specify how usage is measured, when billing occurs, and what happens in the event of non-payment.
- Suspension: in case of non-payment or misuse, you may temporarily block access.
- Revocation: under what conditions and with what notice period you terminate the license.
- Consequences: what happens to API keys and processed data after termination.
Honest recommendation
An API license is not a formality but the foundation of your product. Anyone opening an API to third parties would be wise to carefully document usage rights, rate limits, liability, intellectual property, GDPR compliance, and payment. Especially when personal data is involved or major customers rely on the connection, sound legal work far outweighs the costs.
You don't always need a lawyer: for a small, free, or internal API with limited data, a straightforward standard agreement often suffices perfectly. As soon as you start billing per call, promise uptime, or process personal data, customization pays off. Read more: API license agreement, drafting an API license , and having an API license drafted.
Frequently Asked Questions
An agreement in which the provider of an API grants another party the right to use that API. It governs usage rights, rate limits, availability, liability, intellectual property, data processing (GDPR), and payment. It is the legal basis for an open connection.
With a software license, the customer receives a copy of the software. With an API license, the customer gains access to a running service. As a result, provisions regarding uptime, rate limits, and data processing carry more weight than with a classic license.
Rate limits are strict limits on the number of calls per period; exceeding them results in error messages. Fair use is a softer standard against excessive use without an exact number. Both protect the provider against overloading and abuse of the infrastructure.
The license determines this. Common practice is a best-efforts obligation or SLA for availability, limiting liability to direct damages, excluding consequential damages, and setting a maximum amount, often the compensation for the last 6 to 12 months.
If personal data flows via the API: yes. Determine who is the controller and who is the processor. If you process data on behalf of the recipient, a data processing agreement is required with agreements regarding security, sub-processors, and data breaches.
Via a fixed subscription, a price per call (pay-per-use), or a combination of a base fee plus usage. The license specifies how usage is measured, when billing occurs, and what happens in the event of non-payment, such as suspension of access.
Typically in the event of non-payment, abuse, exceeding rate limits, or violation of the terms. The license governs suspension, the notice period upon termination, and the consequences: revocation of API keys and what happens to processed data after expiration.
