Fantasy

Build AI agents with Go. Multi-provider, multi-model, one API.

1. Choose a model and provider
2. Add some tools
3. Compile to native machine code and let it rip

Note

Fantasy is currently a preview. Expect API changes.

import"charm.land/fantasy"import"charm.land/fantasy/providers/openrouter"// Choose your fave provider.provider, err:=openrouter.New(openrouter.WithAPIKey(myHotKey))
iferr!=nil {
fmt.Fprintln(os.Stderr, "Whoops:", err)
os.Exit(1)
}
ctx:=context.Background()
// Pick your fave model.model, err:=provider.LanguageModel(ctx, "moonshotai/kimi-k2")
iferr!=nil {
fmt.Fprintln(os.Stderr, "Dang:", err)
os.Exit(1)
}
// Make your own tools.cuteDogTool:=fantasy.NewAgentTool(
"cute_dog_tool",
"Provide up-to-date info on cute dogs.",
fetchCuteDogInfoFunc,
)
// Equip your agent.agent:=fantasy.NewAgent(
model,
fantasy.WithSystemPrompt("You are a moderately helpful, dog-centric assistant."),
fantasy.WithTools(cuteDogTool),
)
// Put that agent to work!constprompt="Find all the cute dogs in Silver Lake, Los Angeles."result, err:=agent.Generate(ctx, fantasy.AgentCall{Prompt: prompt})
iferr!=nil {
fmt.Fprintln(os.Stderr, "Oof:", err)
os.Exit(1)
}
fmt.Println(result.Response.Content.Text())

🍔 For the full implementation and more see the examples directory.

Multi-model? Multi-provider?

Yeah! Fantasy is designed to support a wide variety of providers and models under a single API. While many providers such as Microsoft Azure, Amazon Bedrock, and OpenRouter have dedicated packages in Fantasy, many others work just fine with openaicompat, the generic OpenAI-compatible layer. That said, if you find a provider that’s not compatible and needs special treatment, please let us know in an issue (or open a PR).

Work in Progress

We built Fantasy to power Crush, a hot coding agent for glamourously invincible development. Given that, Fantasy does not yet support things like:

• Image models
• Audio models
• PDF uploads
• Provider tools (e.g. web_search)

For things you’d like to see supported, PRs are welcome.

Whatcha think?

We’d love to hear your thoughts on this project. Need help? We gotchu. You can find us on:

• Slack
• Discord
• Twitter
• The Fediverse
• Bluesky

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Part of Charm.

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