Once an app relies on an LLM in production, teams quickly need two things: a way to keep track of the prompts they're sending (so a change doesn't silently break something), and a way to test whether a prompt actually works before it ships. PromptLayer and promptfoo both address this, but from opposite directions — one is a hosted platform built for teams with non-engineers editing prompts, the other is a free, open-source tool built for engineers who want testing to live in their code and CI pipeline.
The short version: pick PromptLayer if you want a hosted, no-install platform where product managers or other non-engineers can safely edit and test production prompts, and per-seat pricing is fine for your team. Pick promptfoo if you want free, local-first evals and red-teaming that plug straight into CI, your prompts never leave your machine, and you're comfortable with a config-driven, engineer-first workflow.
PromptLayer, in more detail
PromptLayer is a collaboration platform for AI teams to manage, test, and monitor the prompts powering their LLM applications. Its standout feature is a prompt CMS that lets non-engineers edit and test prompts without needing a code deploy — combined with an eval harness and observability in the same product, plus deployment approval workflows on higher tiers.
Pricing: free for 5 users and 2,500 requests/month, Pro at $49/month for small teams, Team at $500/month (25 users, 100k+ requests), and custom Enterprise pricing that includes a HIPAA BAA and RBAC.
Limits to know: it's closed-source with no self-hosted option, and it competes in a crowded category against a strong open-source alternative, Langfuse.
promptfoo, in more detail
promptfoo is an open-source tool for LLM evaluation and red-teaming: it tests prompts, compares models, and catches jailbreaks or data leaks, both locally and in CI. It's MIT-licensed and free for local and CI use, with an enterprise tier available on request.
Limits to know: there's no team UI unless you're on the enterprise tier, and the config-driven workflow has a real learning curve compared to a point-and-click platform.
Side by side
| PromptLayer | promptfoo | |
|---|---|---|
| Model | Closed-source, hosted platform | Open-source (MIT), local-first |
| Pricing | Free (5 users/2.5k req), Pro $49/mo, Team $500/mo | Free for local/CI use; enterprise on request |
| Best for | Teams with non-engineers editing production prompts | Engineers and security teams doing evals/red-teaming |
| Key strength | Prompt CMS + eval + observability in one product | Free red-teaming and evals wired into CI, data stays local |
| Main limitation | No self-hosted option | No team UI without the enterprise tier |
Verdict
These two aren't really fighting for the same buyer. If your prompts are edited by product managers or other non-engineers and you want a hosted CMS with observability built in, PromptLayer is the more direct fit — you're paying for convenience and a UI everyone on the team can use. If your team is engineering-only, cares about data never leaving your infrastructure, and wants automated red-teaming and evals running in CI on every pull request for free, promptfoo is the better starting point. Plenty of teams end up using both: promptfoo in CI to catch regressions, and something like PromptLayer for day-to-day prompt collaboration.