API reference

Spec: openapi.json (OpenAPI 3.1). Signup endpoints live at https://kilowatt.sh and need no auth.

Checkout: reserve a founding spot

POST /api/checkout

Creates a Stripe Checkout session (subscription mode) and returns its URL. The human opens it and pays. No auth.

Body (JSON, or application/x-www-form-urlencoded, which redirects straight to Checkout with 303):

Field Type Required Notes
plan string no pro ($39/month, default) or lite ($19/month)
email string no Prefills Checkout. Format and mail domain are checked
agent boolean no true if an AI agent is calling
ref string no Where you found Kilowatt (max 100 chars)

Responses:

Status Meaning
201 {"ok":true,"checkout_url":"https://checkout.stripe.com/...","session_id":"cs_...","plan":"pro","price_usd_month":39,"expires_at":"...","founding_spots_left":N}
400 Bad plan or email
409 founding_full (all 100 reserved; use the waitlist) or already_reserved (email already has a spot)
503 checkout_unavailable; use the waitlist

After payment, Stripe sends the subscriber to https://kilowatt.sh/welcome?session_id=..., which shows the spot number and a billing-portal button. The spot is recorded by a signature-verified Stripe webhook.

GET /api/checkout

checkout_open, founding_cap, founding_reserved, founding_spots_left, and the plans with prices.

Billing

Cancel anytime from the billing portal. Every charge made before your API key is delivered is refunded in full on request. If we don't deliver your key, we refund every charge. Manage or cancel at kilowatt.sh/account.

Waitlist (free, doesn't reserve a spot)

POST /api/waitlist

No auth. Idempotent per email (case-insensitive).

Field Type Required Notes
email string yes Max 254 chars; format and mail domain are checked
use_case string no Max 500 chars
agent boolean no true if an AI agent is submitting
plan string no pro, lite, or undecided
ref string no Max 100 chars. Also accepted as ?ref=

Headers: X-Client: <agent name> (optional, stored).

Status Meaning
201 Added. Body has position, message, and current counts
200 Email already registered; same body with already_registered: true
303 Form posts redirect to /?joined=<position>#join
400 Validation error: {"ok":false,"error":"..."}
429 Rate limited (5 new signups per 10 min per IP, 20 per /24 network). Retry-After header and retry_after_seconds

GET /api/waitlist

Counts: founding_cap, founding_reserved, founding_spots_left, checkout_open, waitlist_signups, total_signups. Real numbers; nothing is padded.

Data and MCP

Inference (with the API key you receive at launch)

Endpoint Compatible with
POST https://api.kilowatt.sh/v1/chat/completions OpenAI Chat Completions
GET https://api.kilowatt.sh/v1/models OpenAI models list
POST https://api.kilowatt.sh/v1/messages Anthropic Messages (Claude Code)

Model ids: deepseek-v4.1-flash, glm-5.3-flash, and auto (router). Auth: Authorization: Bearer <key> (OpenAI) or x-api-key / ANTHROPIC_AUTH_TOKEN (Anthropic). Limit errors are HTTP 429 with Retry-After. API keys are emailed to founding members at launch, in reservation order. Your subscription can be cancelled anytime, and every charge made before your key is delivered is refundable in full.

Agents: /docs/api.md is this page in markdown, or request it with Accept: text/markdown.