diff --git a/tools/osv-linter/internal/pkgchecker/ecosystems.go b/tools/osv-linter/internal/pkgchecker/ecosystems.go
index 7152dce..52b62c3 100644
--- a/tools/osv-linter/internal/pkgchecker/ecosystems.go
+++ b/tools/osv-linter/internal/pkgchecker/ecosystems.go
@@ -133,7 +133,7 @@ func VersionsExistInEcosystem(pkg string, versions []string, ecosystem string) e
 	case "CRAN":
 		return nil
 	case "crates.io":
-		return nil
+		return versionsExistInCrates(pkg, versions)
 	case "Debian":
 		return nil
 	case "GIT":
diff --git a/tools/osv-linter/internal/pkgchecker/ecosystems_test.go b/tools/osv-linter/internal/pkgchecker/ecosystems_test.go
index 4eba81a..4875c49 100644
--- a/tools/osv-linter/internal/pkgchecker/ecosystems_test.go
+++ b/tools/osv-linter/internal/pkgchecker/ecosystems_test.go
@@ -2,6 +2,70 @@ package pkgchecker
 
 import "testing"
 
+func Test_versionsExistInCrates(t *testing.T) {
+	t.Parallel()
+
+	type args struct {
+		pkg      string
+		versions []string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+	}{
+		{
+			name: "multiple_versions_which_all_exist",
+			args: args{
+				pkg:      "defmt",
+				versions: []string{"0.0.0", "0.3.0", "0.3.100-rc.1", "1.0.0-rc.1", "1.0.1"},
+			},
+			wantErr: false,
+		},
+		{
+			name: "multiple_versions_with_one_that_does_not_exist",
+			args: args{
+				pkg:      "defmt",
+				versions: []string{"1.1", "0.3.6-beta", "1.1.2"},
+			},
+			wantErr: true,
+		},
+		{
+			name: "an_invalid_version",
+			args: args{
+				pkg:      "defmt",
+				versions: []string{"!"},
+			},
+			wantErr: true,
+		},
+		{
+			name: "an_invalid_package",
+			args: args{
+				pkg:      "!",
+				versions: []string{"1.0.0"},
+			},
+			wantErr: true,
+		},
+		{
+			name: "a_package_that_does_not_exit",
+			args: args{
+				pkg:      "not-a-real-package-hopefully",
+				versions: []string{"1.0.0"},
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			if err := versionsExistInCrates(tt.args.pkg, tt.args.versions); (err != nil) != tt.wantErr {
+				t.Errorf("versionsExistInCrates() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
 func Test_versionsExistInGo(t *testing.T) {
 	type args struct {
 		pkg      string
diff --git a/tools/osv-linter/internal/pkgchecker/version_check.go b/tools/osv-linter/internal/pkgchecker/version_check.go
index 227ada2..ec3fb33 100644
--- a/tools/osv-linter/internal/pkgchecker/version_check.go
+++ b/tools/osv-linter/internal/pkgchecker/version_check.go
@@ -15,6 +15,58 @@ import (
 	"golang.org/x/mod/semver"
 )
 
+// Confirm that all specified versions of a package exist in crates.io.
+func versionsExistInCrates(pkg string, versions []string) error {
+	packageInstanceURL := fmt.Sprintf("%s/%s", EcosystemBaseURLs["crates.io"], pkg)
+
+	resp, err := faulttolerant.Get(packageInstanceURL)
+	if err != nil {
+		return fmt.Errorf("unable to validate package: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unable to validate package: %q for %s", resp.Status, packageInstanceURL)
+	}
+
+	// Parse the known versions from the JSON.
+	respJSON, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return fmt.Errorf("unable to retrieve JSON for %q: %v", pkg, err)
+	}
+	// Fetch all known versions of package.
+	versionsInRepository := []string{}
+	releases := gjson.GetBytes(respJSON, "versions")
+	releases.ForEach(func(key, value gjson.Result) bool {
+		versionsInRepository = append(versionsInRepository, value.Get("num").String())
+		return true // keep iterating.
+	})
+	// Determine which referenced versions are missing.
+	versionsMissing := []string{}
+	for _, versionToCheckFor := range versions {
+		versionFound := false
+		vc, err := semantic.Parse(versionToCheckFor, "RubyGems")
+		if err != nil {
+			versionsMissing = append(versionsMissing, versionToCheckFor)
+			continue
+		}
+		for _, pkgversion := range versionsInRepository {
+			if r, err := vc.CompareStr(pkgversion); r == 0 && err == nil {
+				versionFound = true
+				break
+			}
+		}
+		if versionFound {
+			continue
+		}
+		versionsMissing = append(versionsMissing, versionToCheckFor)
+	}
+	if len(versionsMissing) > 0 {
+		return &MissingVersionsError{Package: pkg, Ecosystem: "RubyGems", Missing: versionsMissing, Known: versionsInRepository}
+	}
+
+	return nil
+}
+
 // Confirm that all specified versions of a package exist in Go.
 func versionsExistInGo(pkg string, versions []string) error {
 	if pkg == "stdlib" || pkg == "toolchain" {