Add MCP server sub-command using mcp-go library

.gitignore

@@ -12,6 +12,7 @@
 *.out
 
 # Build artifacts
+slack
 slack-cli
 slack_*
 

README.md

@@ -37,12 +37,51 @@ Add this to your prompt (e.g. `AGENTS.md`):
 ```markdown
 - You can send messages to a Slack user by using the `slack send-message <channel|email> "<message>"` command.
 - The message supports Markdown formatting which will be automatically converted to Slack's Mrkdwn format.
+- For AI assistants supporting MCP (Model Context Protocol), you can use `slack mcp-server` to enable tool-based Slack integration.
 ```
 
 ## Usage
 
+### Direct CLI Usage
+
 ```bash
 Usage:
   slack configure                                   - configure Slack token (reads from stdin)
   slack send-message <channel|email> <message>      - send a message to a user
+  slack mcp-server                                  - start MCP server (Model Context Protocol)
+```
+
+**Example:**
+```bash
+slack send-message alex_collins@intuit.com "I love this tool! It makes Slack integration so easy."
 ```
+
+### MCP Server Mode
+
+The MCP (Model Context Protocol) server allows AI assistants and other tools to interact with Slack through a standardized JSON-RPC protocol over stdio. This enables seamless integration with AI coding assistants and other automation tools.
+
+**Setup:**
+
+1. First, configure your Slack token (stored securely in the system keyring):
+   ```bash
+   echo "xoxb-your-slack-token" | slack configure
+   ```
+
+2. Add the MCP server configuration to your MCP client:
+   ```json
+   {
+     "mcpServers": {
+       "slack": {
+         "command": "slack",
+         "args": ["mcp-server"]
+       }
+     }
+   }
+   ```
+
+The server exposes a `send_message` tool that accepts:
+- `identifier` - Slack channel ID (e.g., 'C1234567890') or user email address (e.g., 'user@example.com')
+- `message` - The message to send (supports Markdown formatting)
+
+**Example usage from an AI assistant:**
+> "Slack alex_collins@intuit.com to say how much you like this tool."

go.mod

@@ -3,15 +3,25 @@ module github.com/kitproj/slack-cli
 go 1.24.4
 
 require (
+	github.com/mark3labs/mcp-go v0.42.0
 	github.com/slack-go/slack v0.17.3
 	github.com/zalando/go-keyring v0.2.6
+	golang.org/x/term v0.36.0
 )
 
 require (
 	al.essio.dev/pkg/shellescape v1.5.1 // indirect
+	github.com/bahlo/generic-list-go v0.2.0 // indirect
+	github.com/buger/jsonparser v1.1.1 // indirect
 	github.com/danieljoos/wincred v1.2.2 // indirect
 	github.com/godbus/dbus/v5 v5.1.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
 	github.com/gorilla/websocket v1.5.3 // indirect
+	github.com/invopop/jsonschema v0.13.0 // indirect
+	github.com/mailru/easyjson v0.7.7 // indirect
+	github.com/spf13/cast v1.7.1 // indirect
+	github.com/wk8/go-ordered-map/v2 v2.1.8 // indirect
+	github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
 	golang.org/x/sys v0.37.0 // indirect
-	golang.org/x/term v0.36.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,32 +1,61 @@
 al.essio.dev/pkg/shellescape v1.5.1 h1:86HrALUujYS/h+GtqoB26SBEdkWfmMI6FubjXlsXyho=
 al.essio.dev/pkg/shellescape v1.5.1/go.mod h1:6sIqp7X2P6mThCQ7twERpZTuigpr6KbZWtls1U8I890=
+github.com/bahlo/generic-list-go v0.2.0 h1:5sz/EEAK+ls5wF+NeqDpk5+iNdMDXrh3z3nPnH1Wvgk=
+github.com/bahlo/generic-list-go v0.2.0/go.mod h1:2KvAjgMlE5NNynlg/5iLrrCCZ2+5xWbdbCW3pNTGyYg=
+github.com/buger/jsonparser v1.1.1 h1:2PnMjfWD7wBILjqQbt530v576A/cAbQvEW9gGIpYMUs=
+github.com/buger/jsonparser v1.1.1/go.mod h1:6RYKKt7H4d4+iWqouImQ9R2FZql3VbhNgx27UK13J/0=
 github.com/danieljoos/wincred v1.2.2 h1:774zMFJrqaeYCK2W57BgAem/MLi6mtSE47MB6BOJ0i0=
 github.com/danieljoos/wincred v1.2.2/go.mod h1:w7w4Utbrz8lqeMbDAK0lkNJUv5sAOkFi7nd/ogr0Uh8=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
+github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
 github.com/go-test/deep v1.1.1 h1:0r/53hagsehfO4bzD2Pgr/+RgHqhmf+k1Bpse2cTu1U=
 github.com/go-test/deep v1.1.1/go.mod h1:5C2ZWiW0ErCdrYzpqxLbTX7MG14M9iiw8DgHncVwcsE=
 github.com/godbus/dbus/v5 v5.1.0 h1:4KLkAxT3aOY8Li4FRJe/KvhoNFFxo0m6fNuFUO8QJUk=
 github.com/godbus/dbus/v5 v5.1.0/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 h1:El6M4kTTCOh6aBiKaUGG7oYTSPP8MxqL4YI3kZKwcP4=
 github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510/go.mod h1:pupxD2MaaD3pAXIBCelhxNneeOaAeabZDe5s4K6zSpQ=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
 github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/invopop/jsonschema v0.13.0 h1:KvpoAJWEjR3uD9Kbm2HWJmqsEaHt8lBUpd0qHcIi21E=
+github.com/invopop/jsonschema v0.13.0/go.mod h1:ffZ5Km5SWWRAIN6wbDXItl95euhFz2uON45H2qjYt+0=
+github.com/josharian/intern v1.0.0/go.mod h1:5DoeVV0s6jJacbCEi61lwdGj/aVlrQvzHFFd8Hwg//Y=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/mailru/easyjson v0.7.7 h1:UGYAvKxe3sBsEDzO8ZeWOSlIQfWFlxbzLZe7hwFURr0=
+github.com/mailru/easyjson v0.7.7/go.mod h1:xzfreul335JAWq5oZzymOObrkdz5UnU4kGfJJLY9Nlc=
+github.com/mark3labs/mcp-go v0.42.0 h1:gk/8nYJh8t3yroCAOBhNbYsM9TCKvkM13I5t5Hfu6Ls=
+github.com/mark3labs/mcp-go v0.42.0/go.mod h1:YnJfOL382MIWDx1kMY+2zsRHU/q78dBg9aFb8W6Thdw=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
+github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/slack-go/slack v0.17.3 h1:zV5qO3Q+WJAQ/XwbGfNFrRMaJ5T/naqaonyPV/1TP4g=
 github.com/slack-go/slack v0.17.3/go.mod h1:X+UqOufi3LYQHDnMG1vxf0J8asC6+WllXrVrhl8/Prk=
+github.com/spf13/cast v1.7.1 h1:cuNEagBQEHWN1FnbGEjCXL2szYEXqfJPbP2HNUaca9Y=
+github.com/spf13/cast v1.7.1/go.mod h1:ancEpBxwJDODSW/UG4rDrAqiKolqNNh2DX3mk86cAdo=
 github.com/stretchr/objx v0.5.2 h1:xuMeJ0Sdp5ZMRXx/aWO6RZxdr3beISkG5/G/aIRr3pY=
 github.com/stretchr/objx v0.5.2/go.mod h1:FRsXN1f5AsAjCGJKqEizvkpNtU+EGNCLh3NxZ/8L+MA=
 github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
 github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/wk8/go-ordered-map/v2 v2.1.8 h1:5h/BUHu93oj4gIdvHHHGsScSTMijfx5PeYkE/fJgbpc=
+github.com/wk8/go-ordered-map/v2 v2.1.8/go.mod h1:5nJHM5DyteebpVlHnWMV0rPz6Zp7+xBAnxjb1X5vnTw=
+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=
 github.com/zalando/go-keyring v0.2.6 h1:r7Yc3+H+Ux0+M72zacZoItR3UDxeWfKTcabvkI8ua9s=
 github.com/zalando/go-keyring v0.2.6/go.mod h1:2TCrxYrbUNYfNS/Kgy/LSrkSQzZ5UPVH85RwfczwvcI=
-golang.org/x/sys v0.26.0 h1:KHjCJyddX0LoSTb3J+vWpupP9p0oznkqVk/IfjymZbo=
-golang.org/x/sys v0.26.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.37.0 h1:fdNQudmxPjkdUTPnLn5mdQv7Zwvbvpaxqs831goi9kQ=
 golang.org/x/sys v0.37.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/term v0.36.0 h1:zMPR+aF8gfksFprF/Nc/rd1wRS1EI6nDBGyWAvDzx2Q=
 golang.org/x/term v0.36.0/go.mod h1:Qu394IJq6V6dCBRgwqshf3mPF85AqzYEzofzRdZkWss=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

main.go

@@ -30,6 +30,7 @@ func main() {
 		fmt.Fprintln(w)
 		fmt.Fprintln(w, "  slack configure                                   - configure Slack token (reads from stdin)")
 		fmt.Fprintln(w, "  slack send-message <channel|email> <message>      - send a message to a user")
+		fmt.Fprintln(w, "  slack mcp-server                                  - start MCP server (Model Context Protocol)")
 		fmt.Fprintln(w)
 	}
 	flag.Parse()
@@ -49,6 +50,8 @@ func run(ctx context.Context, args []string) error {
 	switch args[0] {
 	case "configure":
 		return configureToken(ctx)
+	case "mcp-server":
+		return runMCPServer(ctx)
 	case "send-message":
 		if len(args) < 3 {
 			return fmt.Errorf("usage: slack send-message <channel|email> <message>")

mcp.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/mark3labs/mcp-go/server"
+	"github.com/slack-go/slack"
+)
+
+// runMCPServer starts the MCP server that communicates over stdio using the mcp-go library
+func runMCPServer(ctx context.Context) error {
+	token := getToken()
+	if token == "" {
+		return fmt.Errorf("Slack token must be set (use 'slack configure' or set SLACK_TOKEN env var)")
+	}
+
+	// disable HTTP/2 support as it causes issues with some proxies
+	http.DefaultTransport.(*http.Transport).ForceAttemptHTTP2 = false
+	api := slack.New(token)
+
+	// Create a new MCP server
+	s := server.NewMCPServer(
+		"slack-cli-mcp-server",
+		"0.1.0",
+		server.WithToolCapabilities(true),
+	)
+
+	// Define the send_message tool
+	sendMessageTool := mcp.NewTool("send_message",
+		mcp.WithDescription("Send a message to a Slack channel or user. You can specify either a channel ID or a user's email address. The message supports Markdown formatting which will be automatically converted to Slack's Mrkdwn format."),
+		mcp.WithString("identifier",
+			mcp.Required(),
+			mcp.Description("The Slack channel ID (e.g., 'C1234567890') or user email address (e.g., 'user@example.com')"),
+		),
+		mcp.WithString("message",
+			mcp.Required(),
+			mcp.Description("The message to send. Supports Markdown formatting."),
+		),
+	)
+
+	// Add the tool handler
+	s.AddTool(sendMessageTool, func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+		identifier, err := request.RequireString("identifier")
+		if err != nil {
+			return mcp.NewToolResultError(fmt.Sprintf("Missing or invalid 'identifier' argument: %v", err)), nil
+		}
+
+		message, err := request.RequireString("message")
+		if err != nil {
+			return mcp.NewToolResultError(fmt.Sprintf("Missing or invalid 'message' argument: %v", err)), nil
+		}
+
+		// Send the message using the existing sendMessage function
+		err = sendMessage(ctx, api, identifier, message)
+		if err != nil {
+			return mcp.NewToolResultError(fmt.Sprintf("Error: %v", err)), nil
+		}
+
+		return mcp.NewToolResultText(fmt.Sprintf("Message sent successfully to %s", identifier)), nil
+	})
+
+	// Start the stdio server
+	return server.ServeStdio(s)
+}

mcp_test.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"context"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestRun_MCPServer(t *testing.T) {
+	// Set SLACK_TOKEN env var to get past token check
+	oldToken := os.Getenv("SLACK_TOKEN")
+	os.Setenv("SLACK_TOKEN", "test-token")
+	defer func() {
+		if oldToken == "" {
+			os.Unsetenv("SLACK_TOKEN")
+		} else {
+			os.Setenv("SLACK_TOKEN", oldToken)
+		}
+	}()
+
+	// Test that mcp-server sub-command is recognized (won't actually run the server in this test)
+	// We would need to mock stdin/stdout to fully test this
+	args := []string{"mcp-server"}
+
+	// We can't easily test the full server without mocking stdin/stdout
+	// but we can verify the command is recognized and doesn't return "unknown sub-command"
+	_ = args
+	// This test just verifies the test setup works
+}
+
+func TestRun_MCPServerMissingToken(t *testing.T) {
+	// Unset SLACK_TOKEN env var
+	oldToken := os.Getenv("SLACK_TOKEN")
+	os.Unsetenv("SLACK_TOKEN")
+	defer func() {
+		if oldToken != "" {
+			os.Setenv("SLACK_TOKEN", oldToken)
+		}
+	}()
+
+	ctx := context.Background()
+	err := run(ctx, []string{"mcp-server"})
+
+	if err == nil {
+		t.Error("Expected error for missing token, got nil")
+	}
+
+	if !strings.Contains(err.Error(), "Slack token must be set") {
+		t.Errorf("Expected 'Slack token must be set' error, got: %v", err)
+	}
+}