diff --git a/internal/output/output.go b/internal/output/output.go
index c56c5d8..c8c6695 100644
--- a/internal/output/output.go
+++ b/internal/output/output.go
@@ -110,6 +110,22 @@ func (o Options) Active() bool {
 	return o.JSONSet || o.JQ != "" || o.Template != ""
 }
 
+// MarkWebMutuallyExclusive declares the standard output flags
+// (--json, --jq, --template) incompatible with --web on cmd. Call
+// from any builder that has both — without this, cobra silently lets
+// both groups coexist and runtime picks --web, discarding the
+// machine-readable request. The C-audit (C5, C15) flagged exactly
+// this footgun.
+//
+// Three independent pair-wise calls (rather than one quadruple call)
+// so cobra still allows the existing legal combinations among
+// --json / --jq / --template.
+func MarkWebMutuallyExclusive(cmd *cobra.Command) {
+	cmd.MarkFlagsMutuallyExclusive("web", FlagJSON)
+	cmd.MarkFlagsMutuallyExclusive("web", FlagJQ)
+	cmd.MarkFlagsMutuallyExclusive("web", FlagTemplate)
+}
+
 // validate enforces mutual exclusion across --jq / --template against
 // each other. --json may combine with --jq or --template because it
 // drives the *projection*; jq/template format the projection.
diff --git a/internal/output/output_test.go b/internal/output/output_test.go
index d568cc8..4bde80d 100644
--- a/internal/output/output_test.go
+++ b/internal/output/output_test.go
@@ -7,6 +7,8 @@ import (
 	"encoding/json"
 	"strings"
 	"testing"
+
+	"github.com/spf13/cobra"
 )
 
 // fakeExporter projects the supplied data through json.Marshal-friendly
@@ -204,3 +206,55 @@ func TestDefaultTemplateFuncs(t *testing.T) {
 		t.Errorf("color stub: got %q", got)
 	}
 }
+
+// TestMarkWebMutuallyExclusive: C-audit C5/C15. When a command has
+// both --web and the standard output flags, supplying both must be
+// rejected at parse time. Three pair-wise groups means --json + --jq
+// stays legal (existing legal combination).
+func TestMarkWebMutuallyExclusive(t *testing.T) {
+	t.Parallel()
+	for _, tc := range []struct {
+		name    string
+		args    []string
+		wantErr bool
+	}{
+		{"web alone", []string{"--web"}, false},
+		{"json alone", []string{"--json", "id"}, false},
+		{"jq alone", []string{"--jq", ".id"}, false},
+		{"template alone", []string{"--template", "{{.id}}"}, false},
+		{"json+jq still legal", []string{"--json", "id", "--jq", ".id"}, false},
+		{"web + json rejected", []string{"--web", "--json", "id"}, true},
+		{"web + jq rejected", []string{"--web", "--jq", ".id"}, true},
+		{"web + template rejected", []string{"--web", "--template", "{{.id}}"}, true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			cmd := newTestCmdWithWebAndOutput()
+			cmd.SetArgs(tc.args)
+			err := cmd.Execute()
+			gotErr := err != nil
+			if gotErr != tc.wantErr {
+				t.Errorf("err: got %v, wantErr=%v", err, tc.wantErr)
+			}
+			// cobra's group-message form: "if any flags in the group
+			// [a b] are set none of the others can be; [...] were all set"
+			if tc.wantErr && err != nil && !strings.Contains(err.Error(), "none of the others can be") {
+				t.Errorf("error should be cobra's mutex form; got: %v", err)
+			}
+		})
+	}
+}
+
+// newTestCmdWithWebAndOutput builds a no-op cobra command that has
+// both `--web` and the output flag set, with the mutex applied.
+func newTestCmdWithWebAndOutput() *cobra.Command {
+	var web bool
+	opts := &Options{}
+	cmd := &cobra.Command{
+		Use:  "x",
+		RunE: func(*cobra.Command, []string) error { return nil },
+	}
+	cmd.Flags().BoolVar(&web, "web", false, "")
+	AddFlags(cmd, opts)
+	MarkWebMutuallyExclusive(cmd)
+	return cmd
+}
diff --git a/pkg/cmd/issue/list/list.go b/pkg/cmd/issue/list/list.go
index 44a68c1..f9cb831 100644
--- a/pkg/cmd/issue/list/list.go
+++ b/pkg/cmd/issue/list/list.go
@@ -88,6 +88,7 @@ func NewCmd(f *cmdutil.Factory) *cobra.Command {
 	cmd.Flags().IntVarP(&opts.Limit, "limit", "L", DefaultLimit, "maximum number of issues to fetch")
 	cmd.Flags().BoolVarP(&opts.Web, "web", "w", false, "open the issues list in a browser")
 	output.AddFlags(cmd, &opts.Exporter)
+	output.MarkWebMutuallyExclusive(cmd)
 	return cmd
 }
 
diff --git a/pkg/cmd/issue/view/view.go b/pkg/cmd/issue/view/view.go
index 8496c25..b788421 100644
--- a/pkg/cmd/issue/view/view.go
+++ b/pkg/cmd/issue/view/view.go
@@ -65,6 +65,7 @@ func NewCmd(f *cmdutil.Factory) *cobra.Command {
 	cmd.Flags().BoolVarP(&opts.Web, "web", "w", false, "open the issue in a browser")
 	cmd.Flags().BoolVarP(&opts.Comments, "comments", "c", false, "include the comment thread inline")
 	output.AddFlags(cmd, &opts.Exporter)
+	output.MarkWebMutuallyExclusive(cmd)
 	return cmd
 }
 
diff --git a/pkg/cmd/pr/list/list.go b/pkg/cmd/pr/list/list.go
index 1458e5b..b3bc350 100644
--- a/pkg/cmd/pr/list/list.go
+++ b/pkg/cmd/pr/list/list.go
@@ -89,6 +89,7 @@ func NewCmd(f *cmdutil.Factory) *cobra.Command {
 	cmd.Flags().IntVarP(&opts.Limit, "limit", "L", DefaultLimit, "maximum number of PRs to fetch")
 	cmd.Flags().BoolVarP(&opts.Web, "web", "w", false, "open the PR list in a browser")
 	output.AddFlags(cmd, &opts.Exporter)
+	output.MarkWebMutuallyExclusive(cmd)
 	return cmd
 }
 
diff --git a/pkg/cmd/pr/view/view.go b/pkg/cmd/pr/view/view.go
index ce89b0a..47ff5c4 100644
--- a/pkg/cmd/pr/view/view.go
+++ b/pkg/cmd/pr/view/view.go
@@ -69,6 +69,7 @@ func NewCmd(f *cmdutil.Factory) *cobra.Command {
 	cmd.Flags().BoolVarP(&opts.Web, "web", "w", false, "open the PR in a browser")
 	cmd.Flags().BoolVarP(&opts.Comments, "comments", "c", false, "include the conversation thread inline")
 	output.AddFlags(cmd, &opts.Exporter)
+	output.MarkWebMutuallyExclusive(cmd)
 	return cmd
 }
 
diff --git a/pkg/cmd/repo/view/view.go b/pkg/cmd/repo/view/view.go
index 5018bd0..088fb4b 100644
--- a/pkg/cmd/repo/view/view.go
+++ b/pkg/cmd/repo/view/view.go
@@ -74,6 +74,7 @@ func NewCmd(f *cmdutil.Factory) *cobra.Command {
 	cmd.Flags().BoolVarP(&opts.Web, "web", "w", false, "open the repository in the browser")
 	cmd.Flags().StringVarP(&opts.Branch, "branch", "b", "", "branch to view the README from (default: default branch)")
 	output.AddFlags(cmd, &opts.Exporter)
+	output.MarkWebMutuallyExclusive(cmd)
 	return cmd
 }