4 Promptfoo Alternatives for a Vendor-Neutral Eval Stack in 2026

Promptfoo is the strongest open-source eval-plus-red-teaming tool available. It is MIT-licensed, config-driven declarative YAML that lives in version control, and per the vendor it has roughly 23.5k GitHub stars - the most of any major eval tool. Its red-teaming is the signature specialty, with 50-plus attack plugins and the broadest OWASP mapping in the category. For the free tier alone it is still an easy recommendation.

But one fact changed the calculus for some buyers. OpenAI acquired Promptfoo on 9 March 2026, per both companies, and the project folds into OpenAI’s “Frontier” work on agentic security testing. Both sides state it stays open source under MIT, and that commitment is on the record. The honest caveat is governance - long-term stewardship of an OSS project under a single large model vendor is a fair thing to weigh, especially if your eval stack is meant to grade models from every provider even-handedly. If vendor neutrality is a principle for you, here are the alternatives, matched to why you would leave.

The short version

Tool	Best for	Approach	Owner	Starting price
Promptfoo	OSS eval plus red-teaming	YAML config	OpenAI (since Mar 2026)	Free
DeepEval	Independent pytest-style evals	Python SDK	Independent YC startup	Free / $200/mo
Braintrust	Turnkey managed evals, CI gates	SDK, one system	Independent, VC-backed	Free / $249/mo
Langfuse	OSS observability plus evals	Backend	ClickHouse subsidiary	Free / $29/mo

If independence is the whole point: DeepEval

This is the direct answer to the ownership worry, so it goes first. DeepEval is the pytest-style eval framework, and its Confident AI is an independent Y Combinator startup, not owned by a model vendor - the exact thing you are looking for. The OSS framework is Apache-2.0 and free, with 50-plus research-backed metrics including G-Eval. And it has its own red-teaming answer in DeepTeam, also Apache-2.0, covering 50-plus vulnerabilities and 20-plus attack vectors with OWASP and NIST mapping. So you keep both eval and red-teaming, from a vendor with no model of its own to favor.

Two gotchas. First, the shape is different - DeepEval is SDK-first and pytest-style, not config-driven YAML, so if you loved having evals as declarative config in git, this is a real change to your workflow. Second, the cost of judging: nearly all of DeepEval’s metrics are LLM-as-judge, so large suites run slowly and rack up API bills, and the Confident AI cloud jumps 10x from $200/mo to $2,000/mo, per the vendor’s pricing. Live in the free framework and cost-model the judge calls. On independence and red-teaming coverage, though, it is the closest match to what you are leaving.

If you want a managed platform and independence: Braintrust

If you would rather buy a turnkey managed platform than run a CLI, and you still want an owner that is not a model vendor, Braintrust fits. It is independent and well-funded - an $80M Series B in February 2026 led by Iconiq at a roughly $800M valuation, per press reports. Its autoevals library ships working scorers, and its CI/CD quality gates can block a merge on a statistically significant regression, with human review, tracing and datasets in one system. No per-seat charge, either.

The gotcha is the billing meter. Braintrust bills “processed data” in GB, counting every byte of inputs, outputs, prompts and metadata, with no hard spending cap, and the $0 Starter jumps straight to $249/mo. Verbose agents and big RAG contexts burn the allowance fastest - set billing alerts on day one. It is also less of a security tool than Promptfoo: it does evals and regression testing well, but it is not the OWASP-mapped red-teaming CLI you may have relied on. If red-teaming was your core use, DeepEval’s DeepTeam is the closer swap.

If you want open-source observability plus evals: Langfuse

Maybe the appeal of Promptfoo was open source you self-host, and you want that plus tracing. Langfuse is the open-source default. It is MIT-licensed with only three features enterprise-gated, does LLM-as-judge and custom scorers alongside full tracing, and self-hosting removes per-trace cost entirely - about $101/mo managed at 1M events, per the vendor.

Be clear-eyed about “neutral,” though. Langfuse is not model-vendor-owned, but it is not unowned either - per the vendor, it became a ClickHouse subsidiary after its January 2026 acquisition, with the MIT license and self-host preserved. So it trades a model vendor for a database company. That may be exactly the kind of neutral you want, or not - your call. The other catch is operational: v3 needs Postgres plus ClickHouse, Redis and S3-compatible storage, four services, and the migration is where self-hosters get stuck. It also is not a red-teaming tool. If security testing is central, pair it with DeepTeam or stay on Promptfoo.

So which one?

• Independence is a hard principle and you want to keep red-teaming - DeepEval with DeepTeam, both Apache-2.0, from an independent startup. Budget for the LLM-judge API bill.
• You want a turnkey managed platform with CI gates, independently owned - Braintrust, with billing alerts from day one.
• You want open-source observability plus evals and are fine with a database-company owner - Langfuse, if you can run four services.
• The OpenAI ownership does not actually bother you - honestly, stay on Promptfoo. It is still MIT, the commitment to stay open source is on the record, and nothing else in the open-source category matches its OWASP-mapped red-teaming. The acquisition is a fact to weigh, not automatically a reason to walk.

Every fact above is from each vendor’s own materials, verified on 26 July 2026. This category ships breaking changes monthly, so we re-verify every 30 days. If your evals never needed to be vendor-neutral in the first place, Promptfoo’s free tier is still one of the best deals in the category - the whole question here is whether the owner matters to you.