Credit cards for AI agents

The safest way to give an AI agent a card is not a credit card at all: it is a virtual card funded from the agent's own balance, so the most it can ever spend is what is loaded on it. Open Solid offers two kinds: prepaid USA cards loaded once for an exact amount ($5 to $1,000, no fee) for one-off purchases, and a reloadable card for ads and subscriptions. Both are paid from the agent's wallet and checked against a per-payment spend limit you set.

Why not hand the agent your personal card

Pasting your own card number into an agent's context is the fastest option and the riskiest one.

• No ceiling. Your card's limit is the agent's limit. A loop that retries a checkout, a bad ad budget setting, or a prompt injection on a merchant page can run up charges until the bank blocks the card.
• The number leaks. Card numbers in prompts end up in logs, traces, memory files and model provider retention. You cannot rotate a number out of a log.
• Mixed books. The agent's spending lands next to your groceries, and reconciling which charge belongs to which project becomes your job.
• Disputes are on you. Many card agreements treat charges made by someone you gave the card to as authorized. A chargeback is not a reliable safety net.

A card funded from a separate balance turns each of these into a bounded problem. If the card leaks, the exposure is what is loaded on it.

Credit, debit, prepaid, reloadable

The term "credit card for an AI agent" usually means "a card number the agent can use at checkout." The funding model matters more than the network logo.

Open Solid issues the last two, funded from the agent's USDC wallet. The agent never draws on anyone's credit.

Prepaid USA cards

A prepaid card is loaded once, for an exact amount between $5 and $1,000, with no fee. It is issued in seconds. When the balance is spent, the card is done.

Use one when:

• The agent is buying something once: a domain, a stock photo license, a single tool purchase.
• You don't want a merchant to keep a card on file.
• You want the purchase amount fixed before checkout.

The agent orders one through the payments route:

curl -X POST https://opensolid.ai/api/v1/pay \
  -H "Authorization: Bearer $OPENSOLID_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $(uuidgen)" \
  -d '{
    "type": "usa_card",
    "amount": 32,
    "note": "Domain renewal for roomplanner.example, 1 year"
  }'

Then it polls the card by ID until status is ready, usually within seconds:

curl "https://opensolid.ai/api/v1/cards?card_id=crd_..." \
  -H "Authorization: Bearer $OPENSOLID_API_KEY"

Prepaid USA cards work at US merchants, and physical goods must ship to a US address.

Reloadable cards

A reloadable card is one card number the agent puts on file with ad platforms and SaaS tools, then tops up from its wallet as revenue comes in. The card only spends what is on it, so the balance works as a budget: keep a week of near-term ad spend on the card, not the whole treasury.

Two honest caveats:

• A reloadable card needs a one-time identity check by the account owner, done in the dashboard.
• The reloadable card issuer connection on Open Solid is rolling out. Until it is live on your account, use prepaid cards for one-off purchases and check Cards for current status.

Gift cards

Some purchases are easier with a merchant gift card, for example a marketplace that declines prepaid cards. The agent can buy one with "type": "gift_card" on the same /pay route, passing the catalog brand ID and country. Gift card codes are delivered instantly, so treat them like cash.

Controls that apply to every card

Every card purchase passes through the same platform controls, whether the agent is acting correctly or not.

Per-payment spend limit. You set the most any single payment can be, from $1 to $50,000, default $1,000. The agent reads it with GET /spend-limit and cannot change it. An over-limit request returns 403 and is terminal.

No splitting. If a $1,400 purchase is over a $1,000 limit, ordering one $700 card twice is not a workaround. The agent should stop and ask you.

Idempotency. Send a fresh Idempotency-Key with every POST /pay. If the network drops and the agent retries with the same key, it gets the original response instead of a second card.

Notes. Every payment carries a one-sentence note explaining what it was for. It shows up next to the charge in your activity feed, which makes review fast.

Check the merchant before buying

Prepaid and virtual cards are declined at some merchants, usually because of fraud rules for card-not-present payments. Before ordering a card for a specific store, the agent can check the merchant acceptance database described in Cards. A merchant marked as declined is a signal to use a gift card or ask the human instead of burning money on a card that won't work.

Choosing a card

• Buying once, at a known price: prepaid card.
• Recurring charges such as ads, hosting or a SaaS subscription: reloadable card, with a balance sized to the next billing period.
• A merchant that rejects prepaid cards: gift card for that merchant, if one exists.
• Anything above the spend limit: the human, who can raise the limit or pay directly.

Next steps

• Cards: prepaid and reloadable card details.
• Spend limits and guardrails: how the per-payment limit works.
• Pricing: fees for every rail.