OpenAI agreed on 9 March 2026 to acquire Promptfoo, a startup that makes tools for testing AI applications and agents for security weaknesses, safety problems and other unwanted behaviour. Promptfoo's co-founders, Ian Webster and Michael D'Angelo, announced the deal on the company's blog, and OpenAI published its own announcement the same day.
Terms were not disclosed. The deal was subject to customary closing conditions. Promptfoo was valued at $86 million after its most recent funding round in July 2025, according to PitchBook data cited by TechCrunch.
Promptfoo's 23-person team is joining OpenAI. The founders said they would keep working with existing customers and users to make sure service and support continue, and that Promptfoo would remain open source.
What Promptfoo built
Webster and D'Angelo founded Promptfoo in 2024 to help developers test AI applications in a systematic way. They wrote that adversarial testing for security, safety and other behavioural risks had turned out to be the biggest obstacle to shipping AI products, particularly at large enterprises.
The company's open-source command-line tool and library are used for red teaming, static scanning and evaluations, and work with models from many providers. Promptfoo said more than 350,000 developers had used its tools, about 130,000 were active each month, and teams at more than 25% of Fortune 500 companies relied on them.
Before Promptfoo, Webster was an engineering leader at Discord, where he started its Platform Ecosystem organisation and built developer APIs, and later led a team building products on large language models. D'Angelo previously led machine learning engineering at Smile Identity.
“Promptfoo built what we believe is a category-defining platform for AI evaluation and security.”
Why OpenAI is buying
Once the deal closes, OpenAI plans to integrate Promptfoo's technology into OpenAI Frontier, its platform for building and running AI agents for businesses. OpenAI said the tools would support automated red teaming, security evaluation of agent workflows, and monitoring for risk and compliance.
Promptfoo's founders said that inside OpenAI they would work on bringing their core technology into the model and infrastructure layers so that teams can find vulnerabilities earlier. They said OpenAI offered more resources and access to research at the model and inference level.
The founders and the funding
Promptfoo raised a $5 million seed round in July 2024 led by Andreessen Horowitz. Shopify chief executive Tobi Lutke, Discord CTO Stanislav Vishnevskiy and Okta co-founder Frederic Kerrest were named as supporters in the announcement. At that point the company said more than 25,000 software engineers, including at Shopify, Amazon and Anthropic, used its open-source tool.
In July 2025 the company raised an $18.4 million Series A led by Insight Partners, with Andreessen Horowitz also investing, and Insight managing director Ganesh Bell joined its board. SecurityWeek reported that the round brought Promptfoo's total funding to $23.4 million. At the time, the company said more than 125,000 developers used its open-source framework and that more than 30 Fortune 500 companies ran its platform in production. It planned to use the money to add support for multi-agent workflows, Model Context Protocol tool calls and voice applications.
In the acquisition announcement, Andreessen Horowitz general partner Zane Lackey said the firm had believed early that AI security would become critical and that Promptfoo had confirmed that view.
What happens to open-source users
The founders said they would continue to maintain the open-source suite as a red teaming, static scanning and evaluation tool for any AI model or application, and would keep supporting a wide range of model providers, not only OpenAI's.
TechCrunch reported that OpenAI expects to keep developing Promptfoo's open-source offering after the deal.
In their farewell post, Webster and D'Angelo thanked Insight Partners, Andreessen Horowitz and their angel investors, as well as the contributors who wrote code, filed issues and ran Promptfoo in production. They described the move to OpenAI as the fastest way to give their work a larger impact.
