Glossary
What is an API?
An application programming interface is a set of defined protocols and tools that lets different software systems communicate and exchange data with each other.
The idea
An API is a contract. It specifies what one system will accept, what it will return, and what it guarantees — without exposing how any of it is implemented.
That separation is what makes software composable. A platform can rebuild everything behind its API without breaking anyone integrated with it, and an integrator can rely on the interface without understanding the system beneath.
APIs in advertising
- Campaign management, for creating and adjusting campaigns programmatically rather than through a dashboard.
- Reporting, for pulling performance data into a warehouse.
- [Conversion tracking](/resources/glossary/conversion-tracking), sending events server-to-server rather than from a browser.
- Bidding, which is an API called thousands of times a second under a hard latency budget.
- [Callbacks](/resources/glossary/callback) and postbacks, where the platform calls you rather than the reverse.
Why being callable now matters more
For most of the web's history an API was for other developers. Increasingly it is for agents.
When an AI agent completes a task on a user's behalf — checking availability, comparing prices, placing an order — it works through whatever interfaces exist. A brand whose catalogue, pricing and availability are exposed cleanly can be used accurately. One whose information is only in rendered pages gets scraped, approximated, or omitted.
This is the practical mechanism behind an agentic conversion, and it is why MCP exists — a standard way for agents to discover and call tools without a bespoke integration each time. Being machine-callable is becoming a distribution question rather than an engineering nicety.
Common questions
What is the difference between an API and an SDK?
An API is the interface; an SDK is a packaged toolkit — usually including a client library for that API — that you install into your application.
Should I expose an API for AI agents?
If your product data is something an agent would need to complete a purchase or recommendation, yes. The alternative is being described from whatever can be scraped, which is where stale prices and invented policies come from.
More in engineering and integration
The interfaces and plumbing an ad stack is wired together with.