How do their growth rates compare?

Prolific has a month-over-month growth rate of -1.8%; Rely.io has -100%.

How does pricing compare?

Prolific: Paid. Usage-based for requesters: you pay participant rewards plus a platform fee, with custom quotes for large or managed programmes. Participants earn per completed study; joining is free. Rely.io: Free Trial, Paid, Contact for Pricing. Rely.io offers a free path to get started — you can create an account and follow the getting-started guide, and a fully set-up public demo portal is available for evaluation. Paid plans and enterprise agreements are quote-based, so larger teams should contact Rely.io directly for pricing. No specific figures are published that we could confirm.

What are alternatives to Prolific and Rely.io?

Other tools in related categories include Notion, Branded, Labelbox, Appen, eesel AI.

Prolific vs Rely.io — Traffic (18.7M vs 0), Pricing & Verdict

Open AI Tools

Prolific vs Rely.io — Traffic (18.7M vs 0), Pricing & Verdict | Open AI Tools

Side-by-Side Traffic & Specification Matrix

Dimension / Metric	Prolific	Rely.io
Official Domain	prolific.com	rely.io
Pricing Model	Paid	Free Trial, Paid, Contact for Pricing
Monthly Visits	18.7M (18,697,671)	0 (0)
MoM Traffic Delta	-352.04K (-1.8%)	-487 (-100%)
Primary Market & Share	🇺🇸 United States (48.8%)	🌐 Global (—)
Direct Visits / mo	12.98M	0
User Rating	4.6	4.3
Supported Platforms	Website	Website

Prolific

High-quality human data for AI training, evaluation, and research

Verified, targetable participant pool

Filter participants by detailed demographic, professional, and behavioural criteria and reach narrow or representative samples rather than a generic crowd.

AI data and human feedback

Collect human preference data for model fine-tuning, run safety evaluations and red-teaming, and use a feedback API to plug humans into automated pipelines.

Built-in data-quality controls

Attention checks, honesty screening, and approval workflows help filter out careless or fraudulent responses before you analyse results.

Fast study launches

Publish a study and begin collecting responses quickly, with tooling that supports screening, quotas, and longitudinal designs.