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foxy-contexts

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Foxy contexts is a library for building context servers supporting Model Context Protocol

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<img alt="main logo" src="./docs/content/assets/logo.png" width="150"/>
   
   <br/>
   Foxy Contexts
</h1>

<h4 align="center">Build MCP Servers Declaratively in Golang</h4>

<p align="center">
  <a href="#features">Features</a> 🦊
  <a href="#tool-example">Tool Example</a> 🦊
  <a href="https://foxy-contexts.str4.io">Docs</a> 🦊
  <a href="https://github.com/strowk/foxy-contexts">Sources</a>
</p>

Foxy contexts is a Golang library for building context servers supporting [Model Context Protocol](https://modelcontextprotocol.io/).

This library only supports server side of the protocol. Using it you can build context servers using declarative approach, by defining [tools](https://modelcontextprotocol.io/docs/concepts/tools), [resources](https://modelcontextprotocol.io/docs/concepts/resources) and [prompts](https://modelcontextprotocol.io/docs/concepts/prompts) and then registering them with your app.Builder, which is using [uber's fx](https://github.com/uber-go/fx) App under the hood and you can inject into its container as well.

With this approach you can easily colocate call/read/get logic and definitions of your tools/resources/prompts in a way that every tool/resource/prompt is placed in a separate place, while Dependency Injection allows you to reuse shared parts like clients, database connections, etc.

## Features

Here is list of features that are implemented and planned:

- [x] Base (lifecycle/ping)
	- [ ] Progress (planned)
- [x] Transports
	- [x] Stdio Transport
	- [x] SSE Transport
	- [x] Streamable HTTP Transport (beta)
- [x] Tools
    - [x] Package toolinput helps define tools input schema and validate arriving input
- [ ] Resources
	- [x] Resources - static
	- [x] Resources - dynamic via Resource Providers
	- [ ] Resources - dynamic via Resource Templates (planned)
	- [ ] Resource Templates completion (planned)
	- [ ] Resource subscriptions
- [x] Prompts
- [x] Prompts Completion
- [x] Functional Testing package foxytest
- [x] Simple building of your MCP server with the power of Dependency Injection
- [ ] Logging via MCP (planned)
- [ ] Sampling (planned)
- [ ] Roots (planned)
- [ ] Pagination (planned)
- [ ] Notifications list_changed (planned)
- [x] Testing - functional tests with foxytest package

Check [docs](https://foxy-contexts.str4.io/) and [examples](https://github.com/strowk/foxy-contexts/tree/main/examples) to know more.

## Tool Example

For example try following

```bash
git clone https://github.com/strowk/foxy-contexts
cd foxy-contexts/examples/list_current_dir_files_tool
npx @modelcontextprotocol/inspector go run main.go
```
, then once inspector is started in browser open http://localhost:6274 and try to use list-current-dir-files.

Here's the code of that example from [examples/list_current_dir_files_tool/main.go](https://github.com/strowk/foxy-contexts/blob/main/examples/list_current_dir_files_tool/main.go) (in real world application you would probably want to split it into multiple files):

```go
package main

import (
	"fmt"
	"os"

"github.com/strowk/foxy-contexts/pkg/app"
	"github.com/strowk/foxy-contexts/pkg/fxctx"
	"github.com/strowk/foxy-contexts/pkg/mcp"
	"github.com/strowk/foxy-contexts/pkg/stdio"
	"go.uber.org/fx"
	"go.uber.org/fx/fxevent"
	"go.uber.org/zap"
)

// This example defines list-current-dir-files tool for MCP server, that prints files in the current directory
// , run it with:
// npx @modelcontextprotocol/inspector go run main.go
// , then in browser open http://localhost:6274
// , then click Connect
// , then click List Tools
// , then click list-current-dir-files

// NewListCurrentDirFilesTool defines a tool that lists files in the current directory
func NewListCurrentDirFilesTool() fxctx.Tool {
	return fxctx.NewTool(
		// This information about the tool would be used when it is listed:
		&mcp.Tool{
			Name:        "list-current-dir-files",
			Description: Ptr("Lists files in the current directory"),
			InputSchema: mcp.ToolInputSchema{
				Type:       "object",
				Properties: map[string]map[string]interface{}{},
				Required:   []string{},
			},
		},

// This is the callback that would be executed when the tool is called:
		func(_ context.Context, args map[string]interface{}) *mcp.CallToolResult {
			files, err := os.ReadDir(".")
			if err != nil {
				return &mcp.CallToolResult{
					IsError: Ptr(true),
					Meta:    map[string]interface{}{},
					Content: []interface{}{
						mcp.TextContent{
							Type: "text",
							Text: fmt.Sprintf("failed to read dir: %v", err),
						},
					},
				}
			}
			var contents []interface{} = make([]interface{}, len(files))
			for i, f := range files {
				contents[i] = mcp.TextContent{
					Type: "text",
					Text: f.Name(),
				}
			}

return &mcp.CallToolResult{
				Meta:    map[string]interface{}{},
				Content: contents,
				IsError: Ptr(false),
			}
		},
	)
}

func main() {
	app.
		NewBuilder().
		// adding the tool to the app
		WithTool(NewListCurrentDirFilesTool).
		// setting up server
		WithName("list-current-dir-files").
		WithVersion("0.0.1").
		WithTransport(stdio.NewTransport()).
		// Configuring fx logging to only show errors
		WithFxOptions(fx.Provide(func() *zap.Logger {
				cfg := zap.NewDevelopmentConfig()
				cfg.Level.SetLevel(zap.ErrorLevel)
				logger, _ := cfg.Build()
				return logger
			}),
			fx.Option(fx.WithLogger(
				func(logger *zap.Logger) fxevent.Logger {
					return &fxevent.ZapLogger{Logger: logger}
				},
			)),
		).
		Run()
}

func Ptr[T any](v T) *T {
	return &v
}

```

foxy-contexts

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