Merge branch 'main' into mcp-client-go

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Alex Akimov 2026-01-28 21:10:32 +01:00 • committed by GitHub
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8 changed files with 295 additions and 12 deletions

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@ -0,0 +1,19 @@
# A Simple MCP Weather Server written in Go
See the [Quickstart](https://modelcontextprotocol.io/quickstart) tutorial for more information.
## Building
```bash
go build -o weather
```
## Running
```bash
./weather
```
The server will communicate via stdio and expose two MCP tools:
- `get_forecast` - Get weather forecast for a location (requires latitude and longitude)
- `get_alerts` - Get weather alerts for a US state (requires two-letter state code)

10
weather-server-go/go.mod Normal file
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@ -0,0 +1,10 @@
module github.com/modelcontextprotocol/quickstart-resources/weather-server-go
go 1.25.1
require github.com/modelcontextprotocol/go-sdk v1.0.0
require (
github.com/google/jsonschema-go v0.3.0 // indirect
github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
)

10
weather-server-go/go.sum Normal file
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@ -0,0 +1,10 @@
github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/jsonschema-go v0.3.0 h1:6AH2TxVNtk3IlvkkhjrtbUc4S8AvO0Xii0DxIygDg+Q=
github.com/google/jsonschema-go v0.3.0/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/modelcontextprotocol/go-sdk v1.0.0 h1:Z4MSjLi38bTgLrd/LjSmofqRqyBiVKRyQSJgw8q8V74=
github.com/modelcontextprotocol/go-sdk v1.0.0/go.mod h1:nYtYQroQ2KQiM0/SbyEPUWQ6xs4B95gJjEalc9AQyOs=
github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
golang.org/x/tools v0.34.0 h1:qIpSLOxeCYGg9TrcJokLBG4KFA6d795g0xkBkiESGlo=
golang.org/x/tools v0.34.0/go.mod h1:pAP9OwEaY1CAW3HOmg3hLZC5Z0CCmzjAF2UQMSqNARg=

244
weather-server-go/main.go Normal file
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@ -0,0 +1,244 @@
package main
import (
"cmp"
"context"
"encoding/json"
"fmt"
"io"
"log"
"net/http"
"strings"
"github.com/modelcontextprotocol/go-sdk/mcp"
)
const (
NWSAPIBase = "https://api.weather.gov"
UserAgent = "weather-app/1.0"
)
type ForecastInput struct {
Latitude float64 `json:"latitude" jsonschema:"Latitude of the location"`
Longitude float64 `json:"longitude" jsonschema:"Longitude of the location"`
}
type AlertsInput struct {
State string `json:"state" jsonschema:"Two-letter US state code (e.g. CA, NY)"`
}
type PointsResponse struct {
Properties struct {
Forecast string `json:"forecast"`
} `json:"properties"`
}
type ForecastResponse struct {
Properties struct {
Periods []ForecastPeriod `json:"periods"`
} `json:"properties"`
}
type ForecastPeriod struct {
Name string `json:"name"`
Temperature int `json:"temperature"`
TemperatureUnit string `json:"temperatureUnit"`
WindSpeed string `json:"windSpeed"`
WindDirection string `json:"windDirection"`
DetailedForecast string `json:"detailedForecast"`
}
type AlertsResponse struct {
Features []AlertFeature `json:"features"`
}
type AlertFeature struct {
Properties AlertProperties `json:"properties"`
}
type AlertProperties struct {
Event string `json:"event"`
AreaDesc string `json:"areaDesc"`
Severity string `json:"severity"`
Description string `json:"description"`
Instruction string `json:"instruction"`
}
func makeNWSRequest[T any](ctx context.Context, url string) (*T, error) {
req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
if err != nil {
return nil, fmt.Errorf("failed to create request: %w", err)
}
req.Header.Set("User-Agent", UserAgent)
req.Header.Set("Accept", "application/geo+json")
client := http.DefaultClient
resp, err := client.Do(req)
if err != nil {
return nil, fmt.Errorf("failed to make request to %s: %w", url, err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
body, _ := io.ReadAll(resp.Body)
return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, string(body))
}
var result T
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
return nil, fmt.Errorf("failed to decode response: %w", err)
}
return &result, nil
}
func formatAlert(alert AlertFeature) string {
props := alert.Properties
event := cmp.Or(props.Event, "Unknown")
areaDesc := cmp.Or(props.AreaDesc, "Unknown")
severity := cmp.Or(props.Severity, "Unknown")
description := cmp.Or(props.Description, "No description available")
instruction := cmp.Or(props.Instruction, "No specific instructions provided")
return fmt.Sprintf(`
Event: %s
Area: %s
Severity: %s
Description: %s
Instructions: %s
`, event, areaDesc, severity, description, instruction)
}
func formatPeriod(period ForecastPeriod) string {
return fmt.Sprintf(`
%s:
Temperature: %d°%s
Wind: %s %s
Forecast: %s
`, period.Name, period.Temperature, period.TemperatureUnit,
period.WindSpeed, period.WindDirection, period.DetailedForecast)
}
func getForecast(ctx context.Context, req *mcp.CallToolRequest, input ForecastInput) (
*mcp.CallToolResult, any, error,
) {
// Get points data
pointsURL := fmt.Sprintf("%s/points/%f,%f", NWSAPIBase, input.Latitude, input.Longitude)
pointsData, err := makeNWSRequest[PointsResponse](ctx, pointsURL)
if err != nil {
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "Unable to fetch forecast data for this location."},
},
}, nil, nil
}
// Get forecast data
forecastURL := pointsData.Properties.Forecast
if forecastURL == "" {
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "Unable to fetch forecast URL."},
},
}, nil, nil
}
forecastData, err := makeNWSRequest[ForecastResponse](ctx, forecastURL)
if err != nil {
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "Unable to fetch detailed forecast."},
},
}, nil, nil
}
// Format the periods
periods := forecastData.Properties.Periods
if len(periods) == 0 {
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "No forecast periods available."},
},
}, nil, nil
}
// Show next 5 periods
var forecasts []string
for i := range min(5, len(periods)) {
forecasts = append(forecasts, formatPeriod(periods[i]))
}
result := strings.Join(forecasts, "\n---\n")
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: result},
},
}, nil, nil
}
func getAlerts(ctx context.Context, req *mcp.CallToolRequest, input AlertsInput) (
*mcp.CallToolResult, any, error,
) {
// Build alerts URL
stateCode := strings.ToUpper(input.State)
alertsURL := fmt.Sprintf("%s/alerts/active/area/%s", NWSAPIBase, stateCode)
alertsData, err := makeNWSRequest[AlertsResponse](ctx, alertsURL)
if err != nil {
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "Unable to fetch alerts or no alerts found."},
},
}, nil, nil
}
// Check if there are any alerts
if len(alertsData.Features) == 0 {
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: "No active alerts for this state."},
},
}, nil, nil
}
// Format alerts
var alerts []string
for _, feature := range alertsData.Features {
alerts = append(alerts, formatAlert(feature))
}
result := strings.Join(alerts, "\n---\n")
return &mcp.CallToolResult{
Content: []mcp.Content{
&mcp.TextContent{Text: result},
},
}, nil, nil
}
func main() {
// Create MCP server
server := mcp.NewServer(&mcp.Implementation{
Name: "weather",
Version: "1.0.0",
}, nil)
// Add get_forecast tool
mcp.AddTool(server, &mcp.Tool{
Name: "get_forecast",
Description: "Get weather forecast for a location",
}, getForecast)
// Add get_alerts tool
mcp.AddTool(server, &mcp.Tool{
Name: "get_alerts",
Description: "Get weather alerts for a US state",
}, getAlerts)
// Run server on stdio transport
if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil {
log.Fatal(err)
}
}

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