building-with-typesafe-jev

[!NOTE] This is an unofficial, community skill. It is not made, reviewed, or endorsed by TypeSafe AI. TypeSafe publishes its own skill at typesafe-ai/skills. See How this differs from the official skill.

Coding agents treat Jev like one more chat model. This skill teaches them to design for it: typed questions, calibrated confidence, and links to 150+ community projects, sorted by how they work, with a code sketch for each pattern. It installs in Claude Code, Codex, Antigravity CLI, Muse, and Muse Code.

Jev is a System One model. It does not write text. You send it content and a set of typed questions, and it answers each one with a value and a calibrated probability, usually in 100 to 200 ms:

• Choice picks one option from a list. Example: route a ticket to billing, shipping, or support.
• Score places the content on a scale you describe. Example: grade a pull request from "ignores the spec" to "meets the spec".
• Noul gives the probability that a yes/no statement is true. Example: "this shell command deletes files outside the project."

Install

claude plugin marketplace add aaddrick/building-with-typesafe-jev

claude plugin install building-with-typesafe-jev@building-with-typesafe-jev

The skill loads on its own when you work on Jev code. To load it by hand, type:

/building-with-typesafe-jev:building-with-typesafe-jev

codex plugin marketplace add aaddrick/building-with-typesafe-jev

codex plugin add building-with-typesafe-jev@building-with-typesafe-jev

Start a new thread. Codex loads the skill when the task matches. To load it by hand, type:

$building-with-typesafe-jev:building-with-typesafe-jev

agy plugin install https://github.com/aaddrick/building-with-typesafe-jev

Check that it installed:

agy plugin list

Start a new session. Antigravity CLI loads the skill when the task matches. To load it by hand, type:

/building-with-typesafe-jev:building-with-typesafe-jev

Coming from Gemini CLI? If agy plugin import gemini brought this extension over, run the install command above anyway so the current copy replaces the imported one.

Muse loads skills from ~/workspace/skills/ on its own computer. Paste this command into a Muse chat and ask Muse to run it:

curl -fsSL https://raw.githubusercontent.com/aaddrick/building-with-typesafe-jev/main/scripts/install_muse.sh | bash

The script copies the skill folder there and rewrites the SKILL.md header into the shape Muse reads. Start a new chat. Muse loads the skill when the task matches. To update, run the command again.

Clone the repository:

git clone https://github.com/aaddrick/building-with-typesafe-jev.git

Install the skill for every project:

muse skills install building-with-typesafe-jev/skills/building-with-typesafe-jev --scope user

Check that it installed:

muse skills list

Start a new session. Muse Code loads the skill when the task matches. To load it by hand, type:

/building-with-typesafe-jev

Copy the skills/building-with-typesafe-jev/ folder into your agent's skills folder. Keep the whole folder. SKILL.md links to the files beside it.

Set up an API key (optional, recommended)

The skill works without a key. With TYPESAFE_API_KEY set in the agent's shell, the agent can check its design against the live API before the code reaches your project. That catches wrong field names, and questions Jev reads differently than you meant. Each call costs a fraction of a cent.

Step 1. Sign in at console.typesafe.ai and open API Keys in the sidebar.

Step 2. Click Create key at the top right.

Step 3. Name the key after where it will live, such as the machine or the agent. Then click Create key.

Step 4. Copy the key now. The console shows it once. If you lose it, create a new one and revoke the old one.

Keep the key in its own file, readable only by you, and export it as TYPESAFE_API_KEY. Agents often start shells without a terminal, so each section puts the key where those shells can see it. Pick your system.

Save the key to a private file:

mkdir -p ~/.config/typesafe && umask 077 && printf 'export TYPESAFE_API_KEY=%s\n' 'YOUR_KEY' > ~/.config/typesafe/env

Load it from ~/.zshenv. Every zsh reads that file, including shells that agents start without a terminal. ~/.zshrc is read only by interactive shells.

echo '[ -f ~/.config/typesafe/env ] && . ~/.config/typesafe/env' >> ~/.zshenv

Open a new terminal and check it. The command prints the length of the key, not the key:

echo ${#TYPESAFE_API_KEY}

Save the key to a private file:

mkdir -p ~/.config/typesafe && umask 077 && printf 'export TYPESAFE_API_KEY=%s\n' 'YOUR_KEY' > ~/.config/typesafe/env

Load it from the top of ~/.bashrc. Ubuntu, Debian, Mint, and Arch start ~/.bashrc with a line that stops early when no terminal is attached. A line below that guard never runs for agent shells. The top of the file is safe on every distribution:

sed -i '1i [ -f ~/.config/typesafe/env ] \&\& . ~/.config/typesafe/env' ~/.bashrc

Open a new terminal and check it:

echo ${#TYPESAFE_API_KEY}

Follow the macOS steps. zsh reads ~/.zshenv the same way on Linux.

fish reads every file in ~/.config/fish/conf.d/, with or without a terminal:

mkdir -p ~/.config/fish/conf.d; and echo 'set -gx TYPESAFE_API_KEY YOUR_KEY' > ~/.config/fish/conf.d/typesafe.fish; and chmod 600 ~/.config/fish/conf.d/typesafe.fish

string length -- $TYPESAFE_API_KEY

Store the key as a user environment variable. New terminals and apps see it. Terminals that are already open do not:

[Environment]::SetEnvironmentVariable('TYPESAFE_API_KEY', 'YOUR_KEY', 'User')

Open a new terminal and check it:

$env:TYPESAFE_API_KEY.Length

WSL: Windows variables do not reach WSL by default. Inside WSL, follow the Linux with bash steps.

An app you start from the dock, the start menu, or a desktop launcher does not read your shell files.

• Windows: the user environment variable above already covers these apps.
• Linux (systemd): add the line TYPESAFE_API_KEY=YOUR_KEY to ~/.config/environment.d/typesafe.conf, then log out and back in.
• macOS: start the app from a terminal, or set the variable in the app's own settings. macOS has no simple per-user file that desktop apps read.

Ask the agent to run echo ${#TYPESAFE_API_KEY} (or $env:TYPESAFE_API_KEY.Length on Windows). If it prints 0 o