Getting your first paying user is hard when there is nothing free to try.
The classic growth playbook — offer a free tier, let people experience the value, convert them to paying — has always required a billing system, a usage database, a rate limiter, and usually a fair amount of code gluing all of it together.
RelAI now handles all of that automatically. You can add a free trial to any monetised API from your dashboard in about thirty seconds, with zero server changes.
How It Works
When you configure a free tier for an endpoint, RelAI intercepts every incoming request before it reaches your payment layer. If the caller still has free calls remaining, the request is forwarded directly — no payment challenge, no 402, no friction.
RelAI tracks each caller individually and counts their usage against the per-user limit you set. When the counter reaches your limit, they start seeing the normal 402 payment flow.
Your server never knows any of this happened.
Setting It Up
Open your API dashboard at relai.fi/dashboard, go to the Free Tier tab, and click Add.
You configure three things:
| Field | Description |
|---|---|
| Per-user limit | How many free calls each individual user gets before they must pay. |
| Global cap _(optional)_ | A hard ceiling across all users combined. Leave blank for no global limit. |
| Reset period | never (lifetime), daily, or monthly. |
* rule that applies to all endpoints on your API.
What the Caller Sees
Callers who still have free calls remaining get a normal 200 response with two extra headers:
X-Free-Calls-Remaining: 4
X-Free-Calls-Total: 5
Once their free calls run out, they receive the standard x402 402 Payment Required response — with the free tier configuration embedded in extensions.freeTier so any smart client or AI agent can explain what happened and guide the user to pay.
The 402 response includes live data:
"freeTier": {
"perBuyerLimit": 5,
"globalCap": 500,
"globalRemaining": 312,
"resetPeriod": "never"
}
For AI Agents via MCP
If your API is exposed as an MCP tool, AI agents browsing your tool list automatically see the free tier information embedded in the tool description:
[FREE TIER] Free tier: 5 free calls per user. Global pool: 312/500 remaining.
An agent that reads this knows exactly how many free calls it has before needing to arrange payment — and can act accordingly without any human intervention.
Practical Patterns
"Try before you pay"
perBuyerLimit: 3 | resetPeriod: never
Every new caller gets three lifetime free calls to evaluate your API. No configuration required on the caller side.
"Daily free quota"
perBuyerLimit: 10 | resetPeriod: daily
Users get ten free calls per day and pay for anything beyond that. Works well for APIs where the value is ongoing daily utility.
"Controlled beta budget"
perBuyerLimit: 100 | globalCap: 1000
Total of 1 000 free calls across all early users, each capped at 100. Once the global budget is spent, everyone moves to paid — you control exactly how much you give away.
"Per-endpoint pricing tiers"
/embed → perBuyerLimit: 50 | resetPeriod: daily
/generate → no free tier
Generous free tier on cheap endpoints, none on the expensive ones. Users experience your platform for free and pay only when they reach for the heavy compute.
Managing Usage
The Free Tier dashboard tab shows live stats per configuration:
- Unique users who have consumed free calls
- Total free calls used
- Global cap progress bar
No Server Changes Required
Your backend API does not need to know about free tiers, counters, or reset periods. RelAI's relay layer handles all of this transparently. The same API that was fully paid yesterday now has a free trial today — with a single dashboard click.
Configure your free tier at relai.fi/dashboard or read the Management API documentation to automate it programmatically.
Written by the RelAI Team.
