Side by side

Arklex vs Promptfoo

Both stand on ai agent evaluation tools. Which one you can start free with, which one lets you read the code, and what each costs once you pay.

Arklex

Free plan APILinuxSelf-hosted

Arklex combines agent simulations, scoring, human review, and regression checks, with both an open-source framework and a hosted UI. Teams should account for its Python and LLM-provider requirements when choosing how to run it.

Visit Arklex

Promptfoo

Free plan Open source APILinuxMac+3

Promptfoo combines prompt evaluation with red-team testing and a broad provider and integration list. The free Community plan has a monthly probe limit; deployment and support needs may point to custom-priced plans.

Visit Promptfoo

The facts

	Arklex	Promptfoo
Free plan	Yes	Yes
Open source	Not published	Yes
Runs on	API, Linux, Self-hosted	API, Linux, Mac, Self-hosted, Web, Windows
Lowest paid plan	Free or on request	Free or on request
Plans published	1	3
Maker	Not published	Not published
Website	arklex.ai	promptfoo.dev
On ai agent evaluation tools	#10 of 28	#6 of 28

Arklex: what it does well

Generates multi-turn tests with synthetic users
Includes seven built-in evaluation metrics
Supports reusable custom metrics in plain language
Can run as a CI quality gate
Open-source ArkSim plan is free

What to know first

Installation requires Python 3.10 through 3.13
An API key from OpenAI, Anthropic, or Google is required
Private cloud deployment is limited to enterprise customers

Promptfoo: what it does well

Lists more than 60 model providers.
Compares outputs across multiple models.
Community includes 10k red-team probes per month.
Offers local, self-hosted, managed-cloud and on-premise options.
Integrates with CI systems and security tools.

What to know first

Requires Node.js 22.22.0 or newer.
Community is limited to 10k red-team probes per month.
Enterprise and On-Premise pricing is custom and not listed.

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