Best API marketplace for AI agents (2026): pay per call, one balance

You fund one Locus Pro balance and connect an agent over hosted MCP or call the HTTP API from your code. The agent searches the catalog, reads a tool’s schema and price, and calls it. Locus pays the provider and charges the call to your balance. There is no subscription per provider and no monthly minimum on the Free plan.

• •Price before the call — The catalog shows each tool’s fixed price or metered range before your agent calls it, and a call can carry a hard credit ceiling.
• •One balance, one ledger — Every call from every provider lands in one ledger with its charge, so you reconcile one bill instead of one per vendor.
• •Bursty workloads fit — Agents can make thousands of calls one day and none the next. You pay for the calls made, not for a plan sized to the peak.

Prices checked November 11, 2026, from the Locus Pro catalog, for some of the most-used endpoints. 1,000 credits equal $1. A fixed price is charged on every successful call. A range is metered from usage; "typically" means the median to the 90th percentile of recent calls. The catalog always shows the current price before a call.

Locus Pro is built for platforms whose users run agents. Your server, or an agent key bound to one customer, calls the same catalog and names the customer in an X-Locus-End-User header. On the Enterprise plan, Locus charges that customer’s own prepaid balance at the catalog base price plus the markup you set, as a percentage, a flat amount per call, or both. Every call is recorded in a ledger you can filter by customer, provider and endpoint, and your customers never open an account with a provider.

Individuals and teams use the same catalog from a self-serve account at the listed base price, with spend caps, per-key budgets and a price ceiling on each call.

Before the provider runs, Locus reserves the most the call can cost as a hold. The call then settles from the result:

• •Provider error or timeout — The hold is released and nothing is charged.
• •Not enough credits — The call stops with HTTP 402 before it runs, and the response says how many credits it needs.
• •A charged call later found failed — The credits are refunded, and a webhook reports the refund.
• •A retry with the same Idempotency-Key — Locus replays the stored result without a second charge.
• •An empty result — There is no blanket refund. A fixed-price call is charged when the provider succeeds; an endpoint priced by returned records settles lower.
• •A dropped stream — A disconnect after the provider accepts a streamed response charges the full hold.

• •High, steady volume with one provider — A provider’s own plan can cost several times less per call at volume. Tavily search is one example; compare before you commit a large workload.
• •Writes and account actions — The catalog is mostly read operations. Posting to X, for example, needs your own X developer account.
• •Live streams and voice — WebSocket APIs such as live transcription and voice agents are not offered. Use the provider directly.
• •Contract terms — If you need a provider’s negotiated rates, its data-processing agreement or an enterprise feature, sign with that provider.