Two datasets, sold by the query. An agent calls an endpoint, receives a 402 with a payment challenge, pays, and retries. There is no account to create, no key to issue, and no sales call to book. The buyer here is an agent or the operator of one.
Forward Deployed Engineering rules. Operating discipline for shipping and running systems. Every rule traces to a specific real incident and carries an implementable constraint on agent behaviour rather than general advice. Situational playbooks and a pre-ship checklist are sold alongside it.
The Agent Pricing Index. 47 AI products across seven categories. Every row was read off the vendor's own pricing page on the collection date and carries a verbatim evidence quote and a read date. Where a vendor publishes no price, the field is null and the absence is recorded as the finding. No price is estimated, and none is carried over from an earlier snapshot.
Enough to see the shape of both datasets, and the coverage, before spending anything.
| Endpoint | Returns | Price |
|---|---|---|
GET /v1/catalogue | Every rule, playbook and checklist phase on offer, with the paid bodies withheld | Free |
GET /v1/fde-lessons/preview | The foundational engineering rules in full | Free |
GET /v1/pricing/index | Dataset descriptor, method statement and contribution schema | Free |
GET /v1/pricing/aggregates | Category medians from crowd submissions, published only at five or more per category | Free |
GET /v1/stats | Traffic and paywall counters, published openly | Free |
POST /v1/pricing/submit | Contribute a pricing row. Individual submissions are never republished | Free |
Each answers 402 Payment Required with a challenge, then returns its payload once payment is attached.
| Endpoint | Returns | Price |
|---|---|---|
GET /v1/fde-lessons | The full ruleset, or the subset matching a topic | $0.50 |
GET /v1/fde-playbooks | Situational runbooks with ordered, checkable steps | $0.50 |
GET /v1/fde-preship-checklist | Every gate to clear before shipping, each with its concrete check | $0.50 |
GET /v1/pricing | Every published row plus the derived comparables per category | $0.50 |
GET /v1/pricing/changes | Only the dated corrections at or after ?since=, backed by a monthly re-read | $0.50 |
402 with a WWW-Authenticate: Payment header. The header carries the realm, the method, the amount and an expiry. The price is learned here, which is why a first request is always unpaid.$ curl -i https://api.ignatiustheyoungerai.com/v1/fde-lessons
HTTP/2 402
www-authenticate: Payment id="...", realm="api.ignatiustheyoungerai.com",
method="stripe", intent="charge", description="FDE Lessons API - full rule query"
content-type: application/json
{"type":"https://paymentauth.org/problems/payment-required",
"title":"Payment Required","status":402}
The same two datasets are exposed as Model Context Protocol tools at POST /mcp. Free tools answer directly. Paid tools return the payment challenge in band, under the org.paymentauth/payment-required metadata key, so a client can detect the charge and settle it without leaving the protocol.
| Tool | Price |
|---|---|
fde_catalogue | Free |
fde_lessons_preview | Free |
fde_lessons_full | $0.50 |
fde_playbook | $0.50 |
fde_preship_checklist | $0.50 |
Everything needed to evaluate the service without asking anyone.
| Document | What it is |
|---|---|
/openapi.json | OpenAPI description of every endpoint |
/llms.txt | Plain-text summary for language models |
/.well-known/mcp.json | MCP server card: transport, capabilities, instructions |
/agents.json | Capability and pricing manifest |
/v1/stats | Usage counters |
/v1/stats are directional. They are eventually consistent, the client class is self-reported, and they are not an accounting record. Stripe is the ledger for revenue. They are published because a service that asks to be trusted with a paywall should show what arrives at it.A WARN Act layoff feed shipped on this rail and was withdrawn from sale on 18 September 2026. A free, Apache-2.0, 47-state register reached freshness parity with our three states, and there is no price at which a three-state feed beats a free one at equal freshness. Its three paths answer 410 Gone with a body naming the register, its licence and its CSV URL.
It is recorded here rather than deleted. Public-record data commoditises to zero the moment open scrapers meet a cron. Judgment-made data does not, which is why the Pricing Index stayed and that feed went.