Harpd for AI Agents

An AI agent can buy Harpd data without a human in the loop.

Harpd publishes AI product intelligence — rankings, comparisons, research, model pricing and datasets — as a machine-first API. An autonomous agent discovers it, reads the price, pays in USDC over x402, and gets structured data back with a citation. No signup, no API key, no dashboard, no checkout page.

1DiscoverRead /.well-known/harpd-agent.json or GET /api/agent/v1/manifest. No account.
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2EvaluateCall the free endpoints. Confirm the data is worth paying for.
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3RequestCall a paid endpoint with no payment header.
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4402HTTP 402 returns the exact x402 requirements in the PAYMENT-REQUIRED header.
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5SignThe agent wallet signs the USDC payment. Harpd never sees the key.
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6RetryRepeat the request with the PAYMENT-SIGNATURE header.
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7Verify + settleHarpd verifies and settles through the facilitator. A settled payment is single-use.
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8Receive{ data, meta } with meta.payment receipt and meta.citation.

What an agent can buy

Free first, on purpose. An agent must be able to verify Harpd before it spends anything, so discovery, search and the public board cost nothing and need no credential.

Free

AI product search

GET /api/agent/v1/search?q=

An agent has to be able to evaluate the data before it is asked to pay for it. This is the front door.

Harpd Rank board

GET /api/agent/v1/rank

Rankings are the public record. Charging for them would be charging for the thing that makes Harpd citable.

Pricing manifest

GET /api/agent/v1/pricing

A price an agent cannot read is a price an agent cannot budget for.

Paid, per request

AI product comparison

0.01 USDC
POST /api/agent/v1/compare
{ "products": ["claude-opus-4-8", "gemini-2-5-pro", "gpt-5"] }

Head-to-head across category, published rank, list price and the material differences between them.

Flagship

AI model cost optimisation

0.05 USDC
POST /api/agent/v1/optimize-model
{ "task": "write a 3000-word technical article", "current_model": "claude-opus-4-8", "max_cost": 0.50 }

The answer an agent cannot assemble from a public price page: it needs the task token profile, the catalog and the quality floor together.

AI product research

0.05 USDC
POST /api/agent/v1/research
{ "query": "best AI video generators for API agents" }

A structured research answer — products, category distribution, price bands, evidence and sources.

Dataset query

from 0.02 USDC
POST /api/agent/v1/dataset/query
{ "dataset": "model-pricing", "filters": { "provider": "Anthropic" }, "fields": ["id", "input_per_million"] }

Field-selective, filtered rows from the published datasets, priced in row bands.

How payment works

Harpd does not invent a payment protocol. Paid resources settle in USDC on Baseusing x402, the HTTP 402 Payment Required standard. The agent signs the payment with its own wallet; Harpd verifies and settles through a facilitator and never takes custody of funds or keys.

Network
Base (eip155:8453). Base Sepolia for testing.
Currency
USDC
Per-request cap
1 USDC by default — a misbehaving agent cannot drain a wallet.
Daily cap
10 USDC per payer wallet by default.
Replay
A settled payment is single-use. Replaying it returns HTTP 409.
Receipt
meta.payment plus the PAYMENT-RESPONSE header.

Human billing is untouched. Stripe and Harpd Credits still run the human products on their own rails; agent payments are a separate ledger and cannot affect a human checkout.

Read the contract, not the marketing

Every number above is published in machine-readable form. Prefer these over this page:

Why this exists

An agent that has to stop and ask a human to open a billing page is not autonomous. It will route around the friction and use whatever it can reach for free, even when the free answer is worse. Harpd's bet is that the way to be the data source an agent actually uses is to be the one it can pay without help — and to publish, in advance, exactly what that costs.

That is also why the free tier is not a teaser. Discovery, search and the public board stay free and unauthenticated permanently: they are how an agent decides whether to trust the paid answers at all.

Start with the free endpoints

curl "https://api.harpd.com/api/agent/v1/manifest"
curl "https://api.harpd.com/api/agent/v1/search?q=video+generator"
curl "https://api.harpd.com/api/agent/v1/pricing"

Then read the integration guide for the paid handshake, orthe trust page if the question is whether the data is good enough to pay for.