---
title: "System One API. One endpoint."
description: "Call System One models through the System One API for classification, scoring, and yes/no checks. Get structured choices, scores, and probabilities; your application controls every action."
canonical: "https://system-one.dev/en/api"
language: "en"
---

# System One API. One endpoint.

Call System One models through the System One API for classification, scoring, and yes/no checks. Get structured choices, scores, and probabilities; your application controls every action.

HTTP + JSON · API key authentication · Prepaid credits

## Make your first HTTP request

Set SYSTEM_ONE_API_KEY on your server, then send the request to the endpoint shown above. Successful evaluations use your account credits.

```sh
curl 'https://system-one.dev/v1/systemone' \
  -H "Authorization: Bearer $SYSTEM_ONE_API_KEY" \
  -H 'Content-Type: application/json' \
  --data '{
    "state": { "message": "I was charged twice." },
    "questions": {
      "team": {
        "type": "choice",
        "instructions": "Who should handle this?",
        "criteria": {
          "billing": "Payments and refunds",
          "support": "Technical issues"
        }
      }
    }
  }'
```
## Three primitives for structured decisions

Send the context as state and define the questions to evaluate. Combine Choice, Score, and Noul in one request; each question is evaluated independently against the same state.

[Choose between Choice, Score, and Noul](https://docs.system-one.dev/en/docs/primitives)
## Choice: select an option

Define a set of options. Get the selected option, a probability for each option, and confidence.
## Score: rate against a rubric

Describe ordered levels. Get a probability-weighted score that can fall between them, along with the distribution and confidence.
## Noul: estimate a yes/no probability

Ask a yes/no question. Get P(true) from 0 to 1, then choose a threshold in your code when you need a boolean.
## Use the TypeScript SDK

Define questions with choice(), score(), and booleanQuestion(). Connect with the same API key and get typed results in your application.

[Connect SDK to hosted API](https://docs.system-one.dev/en/docs/getting-started)
## Compare Clairic and decision models

This list shows every decision model you can call on system-one.dev, including Clairic. Each page says what inputs it can read, how many questions you can ask at once, and how many credits a call costs.

### Jev

Provided by: system-one.dev

TypeSafe's decision model. It reads text and JSON and returns a choice, a score, or a yes/no answer.

- Provided by: system-one.dev
- 1 credit per question per 4KB
- Up to 32 questions · 64KB per request
- Inputs: text and JSON
- Pick one: up to 255 options; Score: 2–10 levels
- Released 2026-09-18

[Model page](https://system-one.dev/en/models/jev)

### Clef Flash

Provided by: system-one.dev

Structured classification and routing for high-volume, cost-sensitive work.

- Provided by: system-one.dev
- 3 credits per question per 4KB
- Up to 32 questions · 13MB per request
- Inputs: text, JSON, and images (PNG, JPEG, WebP)
- Images: up to 4 · 4MB each · 8MB total
- Pick one: up to 255 options; Score: 2–10 levels
- Released 2026-10-01

[Model page](https://system-one.dev/en/models/clef-flash)

### Clef

Provided by: system-one.dev

The highest-priced of the three Clef models. It reads text, JSON, and images and returns a choice, a score, or a yes/no answer.

- Provided by: system-one.dev
- 6 credits per question per 4KB
- Up to 32 questions · 13MB per request
- Inputs: text, JSON, and images (PNG, JPEG, WebP)
- Images: up to 4 · 4MB each · 8MB total
- Pick one: up to 255 options; Score: 2–10 levels
- Released 2026-10-01

[Model page](https://system-one.dev/en/models/clef)

### Clef Omni

Provided by: system-one.dev

A decision model that reads text and images and returns a choice, a score, or a yes/no answer.

- Provided by: system-one.dev
- 4 credits per question per 4KB
- Up to 32 questions · 13MB per request
- Inputs: text, JSON, and images (PNG, JPEG, WebP)
- Images: up to 4 · 4MB each · 8MB total
- Pick one: up to 255 options; Score: 2–10 levels
- Released 2026-10-09

[Model page](https://system-one.dev/en/models/clef-omni)

### Decider

Provided by: system-one.dev

Reads text and JSON and returns a choice, a score, or a yes/no answer.

- Provided by: system-one.dev
- 1 credit per question per 4KB
- Up to 32 questions · 64KB per request
- Inputs: text and JSON
- Pick one: up to 255 options; Score: 2–10 levels
- Released 2026-10-07

[Model page](https://system-one.dev/en/models/decider-v1-1)

### Clairic

Provided by: system-one.dev

An extraction model that returns typed values from text, JSON and images.

- Provided by: system-one.dev
- 2 credits per 4KB of input
- Inputs: text, JSON, and images (PNG, JPEG, WebP)
- Images: up to 4 · 4MB each · 8MB total
- Released 2026-10-19

[Model page](https://system-one.dev/en/models/clairic)

Prices are in credits. Token usage is shown for reference only; you are charged by model, number of questions and 4KB blocks.


## Start calling System One

### Create a key

Create an API key in the console and save it in your server environment. The full key is shown once.

### Send a request

Copy the cURL example, or use your HTTP client. No SDK installation is required.

### Review usage

Check request status, credit charges, and your remaining balance in the console.

## Authentication

Sign in or create an account, complete any required email verification, then open API keys and create a named key. The complete key is displayed once. Copy it into your server environment or secret manager. The website Playground uses the signed-in session; external applications use the platform key.

[Authentication](https://system-one.dev/en/auth.md)
## Failure and retry accounting

Credits are reserved before inference and returned on a recorded failed inference. A successful replay using the same Idempotency-Key and body incurs no new inference or debit while its replay record remains available. Different input with the same key is rejected. After a timeout or uncertain result, check recorded usage before retrying and preserve the key. Reconciliation can be pending; do not assume a refund until the recorded outcome confirms it.

## Start here

- [Developer documentation](https://docs.system-one.dev/en)
- [Versioning and deprecation](https://docs.system-one.dev/en/docs/api/versioning)
- [Idempotency and retries](https://docs.system-one.dev/en/docs/api/idempotency)
- [API errors](https://docs.system-one.dev/en/docs/api/errors)
- [TypeScript SDK](https://system-one.dev/en/sdk)
- [API reference](https://system-one.dev/en/api)
- [Models](https://system-one.dev/en/models)
- [Model catalog](https://docs.system-one.dev/en/docs/models)
- [Authentication](https://system-one.dev/en/auth.md)
- [Pricing](https://system-one.dev/en/pricing)
- [Credit billing](https://docs.system-one.dev/en/docs/billing)
- [OpenAPI specification](https://system-one.dev/openapi.json)
- [Agent integration guide](https://system-one.dev/en/skill.md)
- [System One for Coding Agents: Cursor, Claude Code, Codex](https://docs.system-one.dev/en/docs/coding-agents)
- [Installable coding-agent skill](https://system-one.dev/skills/system-one/SKILL.md)
- [About](https://system-one.dev/en/about)
- [Contact](https://system-one.dev/en/contact)
- [Playground samples](https://system-one.dev/en/demo)
- [Blog](https://system-one.dev/en/blog)
- [SDK source](https://github.com/ziyu/system-one-sdk)
- [@system-one-ai/core (npm)](https://www.npmjs.com/package/@system-one-ai/core)