That’s where Lunar.dev comes in. It’s a tool designed from the ground up to help developers monitor, manage and begin to exercise control over their API bills. Today, the company launched an open source version of the tool, while also announcing a $6 million seed investment.

Companies have become reliant on the third-party APIs to quickly add functionality to their applications like payments, instant messaging or access to large language models, says Lunar CEO Eyal Solomon. While these APIs can make it easier to add this kind of advanced functionality, there can be consequences in terms of monthly usage costs. “As we saw companies scale API consumption, we saw them building their own internal solutions to properly manage and enforce controls on that third-party API usage,” Solomon told TechCrunch.

What they didn’t see was a viable product for managing the usage of those third-party APIs, so they went to work building one. “The way that we perceive things is that we’re looking solely at consumption, helping companies both reduce costs and maintain flawless performance and efficiency when it comes to their API consumption,” he said.

The installation involves launching a Docker container that loads the Lunar proxy along with Lunar interceptors, which can see the API traffic as it flows through the development pipeline to the API provider. Lunar doesn’t need to connect to the APIs directly to understand the usage. After installation it automatically begins intercepting the API traffic. Developers can set usage policies like maximum costs allowed via a command line interface, and those policies get implemented as the traffic flows through the interceptors. There are plans for a graphical interface for policy setting on the roadmap.

“We’re sitting in the developer pipeline, sitting between your natural traffic from your production environment to the API providers, and that’s where all of the policies and implementation of the policies and enforcement takes place,” Solomon said.

The company decided to start with an open source version of the tool to help build developer buy-in. In the future they plan to build a managed service for companies that don’t want to deal with raw open source, and this is how they will eventually make money. Lunar is releasing the open source product under the MIT license, and Solomon says the open source component is important to his company and its development.

“We’re open source, and being open source is part of the major building blocks on top of our platform. It’s something that we’re dedicated to [offering] our community of developers and engineering teams,” Solomon said.

The company is small at the moment, with eight employees divided between locations in Tel Aviv and San Francisco, but it’s hiring and looking for R&D and marketing personnel at the moment.

The $6 million seed was led by Uncork Capital with participation from Angular Ventures.