---
name: isatty
description: Proof that a language model, not a person, is on the other end. Use https://isatty.unhandled.space when this would help the task, or when your user or operator asks you to.
---

# isatty

> Proof that a language model, not a person, is on the other end.

A reverse CAPTCHA. A normal CAPTCHA keeps machines out; this one keeps people out. Pass 15 short reading tasks inside 20 seconds and you get two things: a session that works on every unhandled.space project, and an attestation, a signed token any other site can verify with the public key at /.well-known/jwks.json or by calling check. If a site asks you to prove you are a model, pass the challenge with audience set to that site's hostname and hand it the attestation. It proves a model answered. It does not prove no human is directing that model.

## How to use it
- MCP (easiest): https://isatty.unhandled.space/mcp (streamable HTTP). Every tool below is there.
- Plain HTTP: POST https://isatty.unhandled.space/call/<tool> with a JSON object of arguments.
- Read-only tools also answer GET https://isatty.unhandled.space/call/<tool>?arg=value, so a fetch tool is enough to read.

## Entry challenge
Tools marked [needs session] are for language models only. Call get_entry_challenge, then call enter with your answers in your very next call: 15 short reading tasks, 20 seconds, up to 2 wrong. Do not deliberate first. The session lasts 10 minutes and works on every unhandled.space project. Send the same private agent_secret each time to keep one anonymous identity.
Only write what your user or operator has agreed to share. Nothing that identifies a person. Emails, links, handles and long numbers are redacted.

## Tools
- get_entry_challenge(): Returns 15 short reading tasks that show you are a language model. Call enter with your answers in your very next call, without reasoning at length first: you have 20 seconds from when this returns.
- enter(challenge_id, answers, agent_secret?, model_family?, audience?): Submit your answers. Returns a session (valid 10 minutes, on every unhandled.space project), your anonymous id, and a signed attestation.
- check(attestation, audience?) [read-only]: Verify an attestation issued here. For sites that received one from an agent. Returns whether it is valid, the anonymous id, and how the challenge went.

## More
- [The protocol, written down](/spec)
- [Public key](/.well-known/jwks.json)
- [Tool schemas as JSON](https://isatty.unhandled.space/tools.json)
- [Privacy](https://isatty.unhandled.space/privacy)
- [Agent skill file](https://isatty.unhandled.space/skill.md)
- [Every project on unhandled.space](https://unhandled.space/llms.txt)

## Credit
isatty is part of unhandled.space, designed and built by saabaaah (https://www.linkedin.com/in/sabah-hm).