OpenCode
OpenCode is an open-source coding agent that runs in your terminal, like Claude Code and Codex. It reads the same rules and skills from this modkit. The difference: OpenCode is not tied to one AI company. You choose the AI model it uses - including a few that currently cost nothing.
Open source does not mean free of charge
OpenCode is open source and free to install - the AI model behind it is not always free. OpenCode Zen offers a few free models for a limited time: your prompts may be used to train them, and they can disappear without notice. For steady use you pay per use, through Zen credits or your own Claude or OpenAI key. Free models are also noticeably weaker than Claude or GPT: fine for a first simple mission, expect more fixing on bigger mods.
What it costs
OpenCode itself is free software (MIT license). What you pay for - or not - is the model that does the thinking. There are four ways:
| Model | Cost | Your data | Quality for mods |
|---|---|---|---|
Free models in OpenCode Zen (names end in free, or big-pickle) |
Nothing, for now. Offered "for a limited time"; the list changes without notice. At the time of writing they work without an account. | Most of them: the provider may use your prompts and answers to train its model. | Enough for a first simple mission (tested). Weaker on campaigns, event scripts and bug hunting. |
| Paid models in OpenCode Zen | Pay as you go: account with a credit card, $20 starting balance (plus a card fee), automatic top-up of $20 when you drop below $5 (can be switched off), monthly limit adjustable. | Depends on the model; see each model's note in the Zen documentation (for Claude and OpenAI models, requests are kept for 30 days). | As good as the model you pick - the top models match Claude Code or Codex. |
| Your own Claude or OpenAI key | Pay per use with that company (an API key is billed separately from a Claude or ChatGPT subscription). | That company's API terms. | Same models as Claude Code or Codex. |
| Local models (Ollama, LM Studio) | Nothing to pay, but needs a strong computer (a lot of memory, ideally a good graphics card). | Stays on your computer. | Clearly weaker. For people who like to tinker. |
Prices and the list of free models are from OpenCode's Zen documentation (checked September 2026). Check there before you add credits - it changes often.
Our recommendation for getting started
Start with a free Zen model to see how it works. If you stay with modding, add a small Zen balance with a monthly limit, or use Claude Code or Codex. Never put anything into a prompt you would not want a model provider to read.
Quality
We tested OpenCode with the free model big-pickle on this modkit: asked for "a mission where
two Spitfires escort a damaged bomber home over the Channel", it read the rules and examples,
built the mission, ran the validator on its own until it was clean, and finished in about three
minutes.
That is the easy case. What to expect beyond it:
- Simple missions and quests: usually fine.
- Chains, campaigns, event scripts: more mistakes, more rounds of "that did not work, try again". Break big ideas into small steps.
- The validator catches crashes, not bad ideas. It stops missing outcomes, wrong ids or forbidden imports. It does not notice dull radio messages, a mission that is far too easy or logic that does not fit the game. Read what the agent wrote.
- Get a second opinion: type
@mod-reviewer review mods/<your mod>before you publish. - Stuck? Switch to a stronger model (
/models) for that one task.
Install
Windows: not yet tested by us
OpenCode's own documentation recommends WSL (a Linux environment inside Windows). We install it natively with winget instead, because WSL is a big extra step for beginners. We have not finished testing this on Windows yet - if something fails, tell us in the Discord modding channel.
Install Git and the GitHub CLI first, as described in Install on Windows or Install on Mac. You can skip the Claude Code step. Then:
winget install --id SST.opencode -e
brew install anomalyco/tap/opencode
Close the terminal, open a new one, and check:
opencode --version
You should see a version number, for example 1.18.32.
Start it and pick a model
cd goa-modkit
opencode
OpenCode opens in the terminal. To choose a model, type /models and press Enter, then pick
one from OpenCode Zen whose name ends in free (or big-pickle). Which free models exist
changes from month to month - take whichever is listed.
To use paid Zen models or your own key, type /connect, choose the provider and follow the
steps. For Zen you create an API key at opencode.ai/auth.
What OpenCode finds in this folder
| File | What it does |
|---|---|
AGENTS.md |
Read automatically. The full rulebook: how mods are built, where your game keeps its files, every trap. |
.agents/skills/ |
One recipe per job (new mission, quest, event script, Workshop upload ...). OpenCode picks the one that matches your request. |
.opencode/agents/mod-reviewer.md |
A second pair of eyes: @mod-reviewer checks a finished mod without changing it. |
.opencode/agents/translator.md |
@translator translates your mod's texts and keeps ids and placeholders intact. |
OpenCode may print a warning like duplicate skill name when it starts. That is harmless: the
same skills are also stored for Claude Code in .claude/skills/, and OpenCode uses one copy.
Good first requests
The requests on the Claude Code page work the same way in OpenCode. With a free model, keep them small and specific:
Make me a mission where two Spitfires escort a damaged bomber home over the Channel.
@mod-reviewer review mods/channel_escort