Backends

A backend is an address and a model. ThinkThen speaks one wire shape, System One, and any server that speaks it can answer.

The built-in backends

Name one with --backend NAME or THINKTHEN_BACKEND. Each brings its own address, key variable and model.

This table gives the last thinkthen check of each built-in backend.

Any other server goes in through its address or the configuration file. Awesome ThinkThen lists more models and servers that pass the check.

With no backend named

A command that names no backend and no address sends every question to https://api.typesafe.ai/v1 with jev-1.13.0. It reads the key from THINKTHEN_API_KEY. The TypeSafe Jev page covers that backend.

question="Does the customer ask for a refund?"

printf '%s\n' "I want to send this back." |
thinkthen decide "$question" --plan |
head -1 |
jq .

{
  "url": "https://api.typesafe.ai/v1/systemone",
  "model": "jev-1.13.0",
  "key_env": "THINKTHEN_API_KEY",
  "request": {
    "state": "Each question quotes the text it asks about.",
    "model": "jev-1.13.0",
    "questions": {
      "q1": {
        "type": "noul",
        "instructions": "The text is \"I want to send this back.\\n\". Does the customer ask for a refund?"
      }
    }
  }
}

--plan sends nothing and needs no key. The plan holds the evidence, so treat it with the same care as the request.

The key

A named backend reads only its own key variables, and the first one that is not blank wins. With no backend named, the key comes from THINKTHEN_API_KEY. The command takes no flag and no file for a key. A key that is unset or blank exits 4 at any address but the three local hosts named below. The message names the variable and never a value.

The key goes only to the address you named. It never shows in a plan, a result, a saved answer, a log line, or an error. An address that holds the key is refused before anything is sent.

A plain http:// address may reach only localhost, 127.0.0.1 or [::1]. Any other http:// host is a usage error, because the key would cross the network in clear text. At those three hosts a request goes out with no key when the key variable is unset, whichever backend is named. Under http:// the tool ignores every proxy variable.

An address with a user name, a query, or a fragment is a usage error. The plan prints the address, and a saved answer keeps it.

Where your text goes

Each backend's own terms govern what it keeps. The default address sends your question and evidence to TypeSafe. Its customer agreement, data processing addendum, and privacy policy describe data handling. The privacy policy, checked 2026-09-28, gives no fixed retention period for API input. Check the terms that govern your account before you send sensitive text. The answer cache has its own storage setting.

Configuration · Every setting and its default · Test it before you trust it