diff --git a/docs/MCP.md b/docs/MCP.md
index 2e432ff..fa302a8 100644
--- a/docs/MCP.md
+++ b/docs/MCP.md
@@ -6,7 +6,7 @@ The trivy-operator-explorer **frontend** ships a built-in [Model Context Protoco
 
 Every read tool (`list_images`, `get_image`, `list_cves`, `list_images_with_cve`) accepts an optional `cluster` input. Set it to a cluster name to scope results to that cluster, or omit it to aggregate across all clusters in the bucket. The ignore-list tools are global (not cluster-scoped), matching the sqlite schema.
 
-The tools are intentionally primitives (`list_images`, `get_image`, `list_cves`, `list_images_with_cve`, `list_ignored_cves`, `ignore_cves`, `unignore_cves`) rather than task-specific helpers. An LLM client composes them to answer ad-hoc questions; worked examples are at the bottom of this page.
+The tools are intentionally primitives (`list_clusters`, `list_images`, `get_image`, `list_cves`, `list_images_with_cve`, `list_ignored_cves`, `ignore_cves`, `unignore_cves`) rather than task-specific helpers. An LLM client composes them to answer ad-hoc questions; worked examples are at the bottom of this page.
 
 ## Configuration
 
@@ -52,6 +52,10 @@ curl -sS -H 'Content-Type: application/json' \
 
 Each tool's full input/output JSON Schema is published over the MCP `tools/list` method. The summary below is the same `description` field returned in that listing.
 
+### `list_clusters` (read)
+
+List the cluster names whose trivy-operator reports are currently available. Call this first in a multi-cluster deployment, then pass a returned name as the optional `cluster` argument on the other read tools to scope results to that cluster (omit it to aggregate across all clusters). Takes no inputs; returns `{total, clusters}`.
+
 ### `list_images` (read)
 
 List every container image known to the cluster (scanned by trivy-operator plus any unscanned images detected via running pods). Returns per-image summary with vulnerability counts grouped by severity, fix-available counts, OS metadata, and the workloads that use the image. Mirrors the filters available at `/api/v1/images`.
diff --git a/internal/mcp/server.go b/internal/mcp/server.go
index a53b2f9..3b2c305 100644
--- a/internal/mcp/server.go
+++ b/internal/mcp/server.go
@@ -62,12 +62,19 @@ func newServer() *mcpsdk.Server {
 const serverInstructions = `Trivy Operator Explorer MCP server.
 
 Read-only and mutating tools for working with the vulnerability reports
-produced by Aqua Security's trivy-operator in a Kubernetes cluster, plus a
-persisted "ignored CVE" list.
+produced by Aqua Security's trivy-operator across one or more Kubernetes
+clusters (collected into a shared S3 bucket), plus a persisted "ignored CVE"
+list.
 
-Use the read tools (list_images, get_image, list_cves, list_images_with_cve,
-list_ignored_cves) to inspect findings, then use the mutating tools
-(ignore_cves, unignore_cves) to manage the ignore list per image.
+Use the read tools (list_clusters, list_images, get_image, list_cves,
+list_images_with_cve, list_ignored_cves) to inspect findings, then use the
+mutating tools (ignore_cves, unignore_cves) to manage the ignore list per image.
+
+Reports come from many clusters. Call list_clusters first to discover the
+available cluster names, then pass one as the optional "cluster" argument on
+list_images/get_image/list_cves/list_images_with_cve to scope results to that
+cluster. Omit "cluster" to aggregate across all clusters. The ignore list is
+global (not cluster-scoped).
 
 Every Vulnerability returned from list_images, get_image, list_cves, and
 list_images_with_cve includes the trivy classification fields "class" (e.g.
diff --git a/internal/mcp/tools.go b/internal/mcp/tools.go
index 9afeb57..7547546 100644
--- a/internal/mcp/tools.go
+++ b/internal/mcp/tools.go
@@ -22,6 +22,13 @@ const defaultRegistry = "index.docker.io"
 // declared via mcp.AddTool so the SDK auto-generates input/output JSON
 // Schemas from the Go types.
 func registerTools(s *mcpsdk.Server) {
+	mcpsdk.AddTool(s, &mcpsdk.Tool{
+		Name: "list_clusters",
+		Description: "List the cluster names whose trivy-operator reports are currently available. " +
+			"Use a returned name as the optional `cluster` argument on the other tools to scope " +
+			"results to a single cluster; omit `cluster` to aggregate across all of them.",
+	}, listClustersTool)
+
 	mcpsdk.AddTool(s, &mcpsdk.Tool{
 		Name: "list_images",
 		Description: "List every container image known to the cluster (scanned by trivy-operator " +
@@ -79,6 +86,27 @@ func registerTools(s *mcpsdk.Server) {
 	}, unignoreCVEsTool)
 }
 
+// ----- list_clusters -----
+
+// listClustersParams intentionally has no fields; list_clusters takes no input.
+type listClustersParams struct{}
+
+// listClustersResult wraps the cluster-name slice in an object so the
+// auto-generated MCP output schema has type "object", which the spec requires
+// for structured tool output.
+type listClustersResult struct {
+	Total    int      `json:"total"`
+	Clusters []string `json:"clusters"`
+}
+
+func listClustersTool(_ context.Context, _ *mcpsdk.CallToolRequest, _ listClustersParams) (*mcpsdk.CallToolResult, listClustersResult, error) {
+	clusters := source.ListClusters()
+	if clusters == nil {
+		clusters = []string{}
+	}
+	return nil, listClustersResult{Total: len(clusters), Clusters: clusters}, nil
+}
+
 // ----- list_images -----
 
 type listImagesParams struct {