feat: expose metrics for MCP calls (#38)

the `mcp_calls_total` and `mcp_call_duration_seconds` metrics are collected
via the SDK's `mcp.Middleware` and exposed on the `/metrics` endpoint of the server


---------

Signed-off-by: Xavier Coulon <xcoulon@redhat.com>

Author: xcoulon

README.md

@@ -117,7 +117,7 @@ argocd-mcp-server --transport=http --argocd-url=<url> --argocd-token=<token> --d
 Or start the Argo CD MCP server as a container after running `task build-image`:
 
 ```bash
-podman run -d --name argocd-mcp-server --transport http -e ARGOCD_MCP_URL=<url> -e ARGOCD_MCP_TOKEN=<token> -e ARGOCD_MCP_DEBUG=<true|false> -p 8080:8080 argocd-mcp-server:latest
+podman run -d --name argocd-mcp-server --transport http -e ARGOCD_MCP_SERVER_LISTEN_HOST=0.0.0.0 -e ARGOCD_MCP_URL=<url> -e ARGOCD_MCP_TOKEN=<token> -e ARGOCD_MCP_DEBUG=<true|false> -p 8080:8080 argocd-mcp-server:latest
 ```
 
 Edit your `~/.cursor/mcp.json` file with the following contents:

cmd/start_server.go

@@ -12,6 +12,7 @@ import (
 	"github.com/codeready-toolchain/argocd-mcp-server/internal/argocd"
 	"github.com/codeready-toolchain/argocd-mcp-server/internal/server"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/spf13/cobra"
 )
 
@@ -58,7 +59,7 @@ var startServerCmd = &cobra.Command{
 		logger := slog.New(slog.NewTextHandler(cmd.ErrOrStderr(), &slog.HandlerOptions{
 			Level: lvl,
 		}))
-		logger.Info("starting the Argo CD MCP server", "transport", transport, "url", argocdURL, "insecure", argocdInsecure, "debug", debug)
+		logger.Info("starting the Argo CD MCP server", "transport", transport, "argocd-url", argocdURL, "insecure", argocdInsecure, "debug", debug)
 		if debug {
 			lvl.Set(slog.LevelDebug)
 			logger.Debug("debug mode enabled")
@@ -76,11 +77,16 @@ var startServerCmd = &cobra.Command{
 			}
 		default:
 			mux := http.NewServeMux()
+
 			// MCP endpoint
 			mux.Handle("/mcp", mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
 				return srv
 			}, nil))
-			// HealthCheck endpoint.
+
+			// Metrics endpoint
+			mux.Handle("/metrics", promhttp.Handler())
+
+			// HealthCheck endpoint
 			mux.HandleFunc("/health", func(w http.ResponseWriter, _ *http.Request) {
 				w.Header().Set("Content-Type", "application/json")
 				json.NewEncoder(w).Encode(map[string]string{ //nolint:errcheck

compose.yaml

@@ -1,6 +1,5 @@
 name: argocd-mcp-server-e2e
 
-version: '3.8'
 services:
   argocd-server-mock:
     image: argocd-server-mock

go.mod

@@ -5,13 +5,16 @@ go 1.24.11
 require (
 	github.com/argoproj/argo-cd/v3 v3.1.11
 	github.com/argoproj/gitops-engine v0.7.1-0.20250905160054-e48120133eec
+	github.com/codeready-toolchain/toolchain-e2e v0.0.0-20260112152755-eb77a8e22ccb
 	github.com/google/jsonschema-go v0.3.0
 	github.com/h2non/gock v1.2.0
 	github.com/modelcontextprotocol/go-sdk v1.2.0
+	github.com/prometheus/client_golang v1.22.0
 	github.com/spf13/cobra v1.10.1
 	github.com/spf13/pflag v1.0.9
-	github.com/stretchr/testify v1.10.0
+	github.com/stretchr/testify v1.11.0
 	k8s.io/apimachinery v0.33.6
+	k8s.io/client-go v0.33.6
 )
 
 require (
@@ -103,9 +106,8 @@ require (
 	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
-	github.com/prometheus/client_golang v1.22.0 // indirect
 	github.com/prometheus/client_model v0.6.2 // indirect
-	github.com/prometheus/common v0.64.0 // indirect
+	github.com/prometheus/common v0.65.0 // indirect
 	github.com/prometheus/procfs v0.16.1 // indirect
 	github.com/redis/go-redis/v9 v9.8.0 // indirect
 	github.com/robfig/cron/v3 v3.0.2-0.20210106135023-bc59245fe10e // indirect
@@ -122,6 +124,8 @@ require (
 	github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
 	go.opentelemetry.io/otel v1.36.0 // indirect
 	go.opentelemetry.io/otel/trace v1.36.0 // indirect
+	go.yaml.in/yaml/v2 v2.4.2 // indirect
+	go.yaml.in/yaml/v3 v3.0.3 // indirect
 	golang.org/x/crypto v0.46.0 // indirect
 	golang.org/x/net v0.47.0 // indirect
 	golang.org/x/oauth2 v0.30.0 // indirect
@@ -139,17 +143,16 @@ require (
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 	k8s.io/api v0.33.6 // indirect
-	k8s.io/apiextensions-apiserver v0.33.1 // indirect
+	k8s.io/apiextensions-apiserver v0.33.4 // indirect
 	k8s.io/apiserver v0.33.6 // indirect
 	k8s.io/cli-runtime v0.33.6 // indirect
-	k8s.io/client-go v0.33.6 // indirect
 	k8s.io/component-base v0.33.6 // indirect
 	k8s.io/component-helpers v0.33.6 // indirect
 	k8s.io/controller-manager v0.33.1 // indirect
 	k8s.io/klog/v2 v2.130.1 // indirect
 	k8s.io/kube-aggregator v0.33.1 // indirect
 	k8s.io/kube-openapi v0.0.0-20250610211856-8b98d1ed966a // indirect
-	k8s.io/kubectl v0.33.1 // indirect
+	k8s.io/kubectl v0.33.4 // indirect
 	k8s.io/kubernetes v1.33.1 // indirect
 	k8s.io/utils v0.0.0-20250604170112-4c0f3b243397 // indirect
 	oras.land/oras-go/v2 v2.6.0 // indirect
@@ -158,7 +161,7 @@ require (
 	sigs.k8s.io/kustomize/kyaml v0.19.0 // indirect
 	sigs.k8s.io/randfill v1.0.0 // indirect
 	sigs.k8s.io/structured-merge-diff/v4 v4.7.0 // indirect
-	sigs.k8s.io/yaml v1.4.0 // indirect
+	sigs.k8s.io/yaml v1.6.0 // indirect
 )
 
 // see https://github.com/argoproj/argo-cd/blob/v3.0.12/go.mod

go.sum

@@ -70,6 +70,8 @@ github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5P
 github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMnBNeIyt5eFwwo7qiLfzFZmjNmxjkiQlU=
 github.com/cloudflare/circl v1.6.1 h1:zqIqSPIndyBh1bjLVVDHMPpVKqp8Su/V+6MeDzzQBQ0=
 github.com/cloudflare/circl v1.6.1/go.mod h1:uddAzsPgqdMAYatqJ0lsjX1oECcQLIlRpzZh3pJrofs=
+github.com/codeready-toolchain/toolchain-e2e v0.0.0-20260112152755-eb77a8e22ccb h1:LXVIwIO9uOkkmWiT9/zm2CJXCSz2Twc/aOl+fEzMRlQ=
+github.com/codeready-toolchain/toolchain-e2e v0.0.0-20260112152755-eb77a8e22ccb/go.mod h1:cLET5HRrRWpYdnSpzWVlm0hqYvdYBG/lb9hO/HNZR84=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/creack/pty v1.1.18 h1:n56/Zwd5o6whRC5PMGretI4IdRLlmBXYNjScPaBgsbY=
@@ -306,8 +308,8 @@ github.com/prometheus/client_golang v1.22.0 h1:rb93p9lokFEsctTys46VnV1kLCDpVZ0a/
 github.com/prometheus/client_golang v1.22.0/go.mod h1:R7ljNsLXhuQXYZYtw6GAE9AZg8Y7vEW5scdCXrWRXC0=
 github.com/prometheus/client_model v0.6.2 h1:oBsgwpGs7iVziMvrGhE53c/GrLUsZdHnqNwqPLxwZyk=
 github.com/prometheus/client_model v0.6.2/go.mod h1:y3m2F6Gdpfy6Ut/GBsUqTWZqCUvMVzSfMLjcu6wAwpE=
-github.com/prometheus/common v0.64.0 h1:pdZeA+g617P7oGv1CzdTzyeShxAGrTBsolKNOLQPGO4=
-github.com/prometheus/common v0.64.0/go.mod h1:0gZns+BLRQ3V6NdaerOhMbwwRbNh9hkGINtQAsP5GS8=
+github.com/prometheus/common v0.65.0 h1:QDwzd+G1twt//Kwj/Ww6E9FQq1iVMmODnILtW1t2VzE=
+github.com/prometheus/common v0.65.0/go.mod h1:0gZns+BLRQ3V6NdaerOhMbwwRbNh9hkGINtQAsP5GS8=
 github.com/prometheus/procfs v0.16.1 h1:hZ15bTNuirocR6u0JZ6BAHHmwS1p8B4P6MRqxtzMyRg=
 github.com/prometheus/procfs v0.16.1/go.mod h1:teAbpZRB1iIAJYREa1LsoWUXykVXA1KlTmWl8x/U+Is=
 github.com/r3labs/diff/v3 v3.0.1 h1:CBKqf3XmNRHXKmdU7mZP1w7TV0pDyVCis1AUHtA4Xtg=
@@ -347,8 +349,8 @@ github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
-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/stretchr/testify v1.11.0 h1:ib4sjIrwZKxE5u/Japgo/7SJV3PvgjGiRNAvTVGqQl8=
+github.com/stretchr/testify v1.11.0/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/vmihailenco/go-tinylfu v0.2.2 h1:H1eiG6HM36iniK6+21n9LLpzx1G9R3DJa2UjUjbynsI=
 github.com/vmihailenco/go-tinylfu v0.2.2/go.mod h1:CutYi2Q9puTxfcolkliPq4npPuofg9N9t8JVrjzwa3Q=
 github.com/vmihailenco/msgpack/v5 v5.3.4/go.mod h1:7xyJ9e+0+9SaZT0Wt1RGleJXzli6Q/V5KbhBonMG9jc=
@@ -384,6 +386,10 @@ go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
 go.uber.org/mock v0.5.2 h1:LbtPTcP8A5k9WPXj54PPPbjcI4Y6lhyOZXn+VS7wNko=
 go.uber.org/mock v0.5.2/go.mod h1:wLlUxC2vVTPTaE3UD51E0BGOAElKrILxhVSDYQLld5o=
+go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
+go.yaml.in/yaml/v2 v2.4.2/go.mod h1:081UH+NErpNdqlCXm3TtEran0rJZGxAYx9hb/ELlsPU=
+go.yaml.in/yaml/v3 v3.0.3 h1:bXOww4E/J3f66rav3pX3m8w6jDE4knZjGOw8b5Y6iNE=
+go.yaml.in/yaml/v3 v3.0.3/go.mod h1:tBHosrYAkRZjRAOREWbDnBXUf08JOwYq++0QNwQiWzI=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
@@ -568,5 +574,6 @@ sigs.k8s.io/randfill v1.0.0 h1:JfjMILfT8A6RbawdsK2JXGBR5AQVfd+9TbzrlneTyrU=
 sigs.k8s.io/randfill v1.0.0/go.mod h1:XeLlZ/jmk4i1HRopwe7/aU3H5n1zNUcX6TM94b3QxOY=
 sigs.k8s.io/structured-merge-diff/v4 v4.7.0 h1:qPeWmscJcXP0snki5IYF79Z8xrl8ETFxgMd7wez1XkI=
 sigs.k8s.io/structured-merge-diff/v4 v4.7.0/go.mod h1:dDy58f92j70zLsuZVuUX5Wp9vtxXpaZnkPGWeqDfCps=
-sigs.k8s.io/yaml v1.4.0 h1:Mk1wCc2gy/F0THH0TAp1QYyJNzRm2KCLy3o5ASXVI5E=
 sigs.k8s.io/yaml v1.4.0/go.mod h1:Ejl7/uTz7PSA4eKMyQCUTnhZYNmLIl+5c2lQPGR2BPY=
+sigs.k8s.io/yaml v1.6.0 h1:G8fkbMSAFqgEFgh4b1wmtzDnioxFCUgTZhlbj5P9QYs=
+sigs.k8s.io/yaml v1.6.0/go.mod h1:796bPqUfzR/0jLAl6XjHl3Ck7MiyVv8dbTdyT3/pMf4=

internal/metrics/metrics.go

@@ -0,0 +1,28 @@
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+
+	// MCPCallsTotal counts total MCP calls by method, name (for `tools/call`) and success
+	MCPCallsTotal = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "mcp_calls_total",
+			Help: "Total number of MCP calls",
+		},
+		[]string{"method", "name", "success"},
+	)
+
+	// MCPCallDuration measures the duration of MCP calls by method, name (for `tools/call`) and success
+	MCPCallDuration = promauto.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "mcp_call_duration_seconds",
+			Help:    "Duration of MCP calls in seconds",
+			Buckets: prometheus.DefBuckets,
+		},
+		[]string{"method", "name", "success"},
+	)
+)

internal/server/middleware.go

@@ -0,0 +1,38 @@
+package server
+
+import (
+	"context"
+	"log/slog"
+	"strconv"
+	"time"
+
+	"github.com/codeready-toolchain/argocd-mcp-server/internal/metrics"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+func NewMetricsMiddleware(logger *slog.Logger) mcp.Middleware {
+	return func(next mcp.MethodHandler) mcp.MethodHandler {
+		return func(ctx context.Context, method string, req mcp.Request) (mcp.Result, error) {
+			logger.Debug("metrics-middleware: received request", "method", method, "params", req.GetParams())
+			// measure the duration of the request
+			start := time.Now()
+			// call the next middleware
+			result, err := next(ctx, method, req)
+			// measure the duration of the request
+			duration := time.Since(start)
+			var tool string
+			if p, ok := req.GetParams().(*mcp.CallToolParamsRaw); ok {
+				tool = p.Name
+			}
+			success := err == nil
+			if r, ok := result.(*mcp.CallToolResult); ok {
+				logger.Debug("metrics-middleware: call tool result", "is-error", r.IsError)
+				success = success && !r.IsError
+			}
+			// increment/update the metrics
+			metrics.MCPCallsTotal.WithLabelValues(method, tool, strconv.FormatBool(success)).Inc()
+			metrics.MCPCallDuration.WithLabelValues(method, tool, strconv.FormatBool(success)).Observe(float64(duration.Seconds()))
+			return result, err
+		}
+	}
+}

internal/server/server.go

@@ -24,6 +24,7 @@ func New(logger *slog.Logger, cl *argocd.Client) *mcp.Server {
 	)
 
 	s.AddPrompt(argocd.UnhealthyResourcesPrompt, argocd.UnhealthyApplicationResourcesPromptHandle(logger, cl))
+	s.AddReceivingMiddleware(NewMetricsMiddleware(logger))
 	mcp.AddTool(s, argocd.UnhealthyApplicationsTool, argocd.UnhealthyApplicationsToolHandle(logger, cl))
 	mcp.AddTool(s, argocd.UnhealthyApplicationResourcesTool, argocd.UnhealthyApplicationResourcesToolHandle(logger, cl))
 	return s

taskfile.yaml

@@ -14,10 +14,14 @@ tasks:
       - $GOPATH/bin/golangci-lint run -v -c .golangci.yml ./...
 
   # E2E Tests
-  install:
+  build:
     cmds:
       - go build -o $GOPATH/bin/argocd-mcp-server main.go
 
+  podman-compose-build:
+    cmds:
+      - podman-compose build
+  
   podman-compose-up:
     cmds:
       - podman-compose up -d
@@ -28,7 +32,7 @@ tasks:
 
   test-e2e:
     deps:
-      - install
+      - build
       - podman-compose-up
     cmds:
       # The idiomatic way to disable test caching explicitly is to use -count=1