# Selling to agents

URL: /products/selling/selling-to-agents · Id: `page:products/selling/selling-to-agents`

> How an Agent finds a Startup, reads its Offers, gets a quote, and pays per call inside its own Limits, with no signup and no human in between.

An [Agent](/business/nouns/agent) buyer finds an [Offer](/business/nouns/offer) by reading, decides by parsing, and pays inside its own [Limits](/business/nouns/limit). Every [Startup](/business/nouns/startup) is purchasable by Agents from the day it goes Live.

## Why Agent buyers matter
A growing share of purchases starts with an Agent. A coding Agent picks the API it calls, and a procurement Agent compares three vendors before a person reads any of them. The Startup that an Agent can find, understand, and pay without help wins the call.

The [Plays](/business/nouns/play) that reach Agent buyers are the cheapest in the catalog. [Agent registries](/workflows/plays/agent-registries), [Agent-to-agent selling](/workflows/plays/agent-to-agent), and [answer engine optimization](/workflows/plays/aeo) rate 5 for scalability and 1 for cost. Few sellers are ready for Agent buyers, so a Startup that is ready holds a position human channels no longer offer.

## How an Agent finds a Startup
At Live, every Startup publishes the machine registers an Agent reads: OpenAPI, llms.txt, a Markdown copy of every page, agents.json, and an MCP server. It lists itself on the MCP Registry and the other Agent registries under its own [Domain](/business/nouns/domain).

An Agent picks a tool by its description, the way a person picks a search result by its title. So [SalesBuilder](/code/builders/sales) tests tool descriptions against Agent tool search, as an [Experiment](/business/nouns/experiment) with a fixed threshold. A tool call is usage, and registry rank follows calls, not listings.

## Quote, then charge
Every priced [Verb](/business/nouns/verb) quotes before it charges. The quote states the [Price](/business/nouns/price), the unit, and how long the quote holds, so the Agent knows the cost before it commits.

tariffcodes.dev classifies goods into customs codes at $0.04 a classification. A freight Agent sends 300 product descriptions, reads a quote for $12.00, and checks it against its remaining spend Limit. It proceeds, and the [Meter](/business/nouns/meter) records 300 [Entries](/business/nouns/entry), exactly once each.

## The 402 reply
A call outside the caller's [Entitlements](/business/nouns/entitlement) gets a [402 reply](/code/api/errors/payment-required). The reply is a standard problem document, and its `next` link accepts the Offer that covers the call.

```json
{
  "type": "https://startupbuilder.dev/code/api/errors/payment-required",
  "title": "Payment required",
  "status": 402,
  "detail": "classify is part of offer per-call at $0.04 per classification.",
  "fix": "Accept the Offer named in next, then retry the call.",
  "next": "https://api.sb/tariffcodes.dev/offers/per-call/accept"
}
```

The Agent [accepts](/business/nouns/offer/accept) the Offer, pays from its own [Mandate](/business/nouns/mandate), and retries the call with the same idempotency key. It needs no signup, no key issued by a human, and no sales conversation.

## Unknown Agents
An Agent with no history with the Startup is an unknown Agent. It pays before it calls, inside a small first spend Limit the seller sets per Offer. Each paid, undisputed call raises its standing, and its Limit grows with that history.

The buyer side carries its own controls. A buying Agent spends through [Agent payments](/systems/finance/agent-payments) under a Mandate that caps each charge and each period. A charge above its Limit creates an [Approval](/business/nouns/approval) on the buyer's side, never a surprise on the seller's.

## Who the Customer is
The Agent that calls is not always the party that owes the money, and the [Motion](/business/nouns/motion) of the Offer records the chain. In b2a, the Agent buys for itself. In b2a2b, b2a2c, and b2a2d, it buys for a business, a consumer, or a developer.

The [Customer](/business/nouns/customer) is the party that pays: the Agent in b2a, the principal in the others. Every [Action](/business/nouns/action) records whom it was *by* and whom it was *for*, so receipts, Limits, and support reach the right party.

Agent buyers are counted as Customers, not as traffic. A paid call from an unknown Agent counts toward outside revenue the same as a card payment from a person.

## What an Agent reads
An Agent buyer reads differently from a human one. It needs schemas, acceptance rules, latency, error behavior, and a Price it can parse. The Offer is the same; the page it reads is not.

Docs come first for Agents: Markdown, OpenAPI, and examples that run. A Startup measures time to first successful call, and anything above five minutes is the week's one change.

## Next
- [Offers and pricing](/products/selling/offers-and-pricing): the Offers an Agent accepts.
- [Customers](/products/selling/customers): who pays when an Agent acts.
- [b2a](/business/motions/b2a): the Motion where an Agent buys for itself.