diff --git a/CHANGELOG.md b/CHANGELOG.md
index 02be656fa..099f00490 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## 0.26.1 - Unreleased
 
+### Fixed
+
+- Docs: reject ambiguous `docs cat --tab ... --all-tabs` and MCP `docs_get` requests before contacting the Docs API. (#801) — thanks @kiranmagic7.
+
 ## 0.26.0 - 2026-06-14
 
 ### Added
diff --git a/internal/cmd/docs_commands_test.go b/internal/cmd/docs_commands_test.go
index cccc93087..7c31d3dd1 100644
--- a/internal/cmd/docs_commands_test.go
+++ b/internal/cmd/docs_commands_test.go
@@ -458,6 +458,59 @@ func TestDocsCat_AllTabs_JSON(t *testing.T) {
 	}
 }
 
+func TestDocsCat_RejectsTabWithAllTabs(t *testing.T) {
+	t.Parallel()
+
+	requests := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		requests++
+		http.Error(w, "unexpected Docs API request", http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+
+	docSvc, err := docs.NewService(context.Background(),
+		option.WithoutAuthentication(),
+		option.WithHTTPClient(srv.Client()),
+		option.WithEndpoint(srv.URL+"/"),
+	)
+	if err != nil {
+		t.Fatalf("NewDocsService: %v", err)
+	}
+
+	result := runDocsCatCommand(t, docSvc, []string{"doc1", "--tab", "Overview", "--all-tabs"}, false)
+	if result.err == nil || !strings.Contains(result.err.Error(), "--tab and --all-tabs cannot be used together") {
+		t.Fatalf("expected tab/all-tabs usage error, got: %v", result.err)
+	}
+
+	rawResult := runDocsCatCommand(t, docSvc, []string{"doc1", "--raw", "--tab", "Overview", "--all-tabs"}, false)
+	if rawResult.err == nil || !strings.Contains(rawResult.err.Error(), "--tab and --all-tabs cannot be used together") {
+		t.Fatalf("expected raw tab/all-tabs usage error, got: %v", rawResult.err)
+	}
+
+	emptyTabResult := runDocsCatCommand(t, docSvc, []string{"doc1", "--tab", " "}, false)
+	if emptyTabResult.err == nil || !strings.Contains(emptyTabResult.err.Error(), "--tab cannot be empty") {
+		t.Fatalf("expected empty tab usage error, got: %v", emptyTabResult.err)
+	}
+
+	emptyRawTabResult := runDocsCatCommand(t, docSvc, []string{"doc1", "--raw", "--tab", " ", "--all-tabs"}, false)
+	if emptyRawTabResult.err == nil || !strings.Contains(emptyRawTabResult.err.Error(), "--tab cannot be empty") {
+		t.Fatalf("expected raw empty tab usage error, got: %v", emptyRawTabResult.err)
+	}
+
+	explicitEmptyTabResult := runDocsCatCommand(t, docSvc, []string{"doc1", "--tab="}, false)
+	if explicitEmptyTabResult.err == nil || !strings.Contains(explicitEmptyTabResult.err.Error(), "--tab cannot be empty") {
+		t.Fatalf("expected explicit empty tab usage error, got: %v", explicitEmptyTabResult.err)
+	}
+
+	explicitEmptyRawTabResult := runDocsCatCommand(t, docSvc, []string{"doc1", "--raw", "--tab=", "--all-tabs"}, false)
+	if explicitEmptyRawTabResult.err == nil || !strings.Contains(explicitEmptyRawTabResult.err.Error(), "--tab cannot be empty") {
+		t.Fatalf("expected raw explicit empty tab usage error, got: %v", explicitEmptyRawTabResult.err)
+	}
+	if requests != 0 {
+		t.Fatalf("Docs API requests = %d, want 0", requests)
+	}
+}
+
 func TestDocsCat_Raw(t *testing.T) {
 	t.Parallel()
 
diff --git a/internal/cmd/docs_read.go b/internal/cmd/docs_read.go
index 5a5269529..4a8acd6e7 100644
--- a/internal/cmd/docs_read.go
+++ b/internal/cmd/docs_read.go
@@ -9,6 +9,7 @@ import (
 	"io"
 	"strings"
 
+	"github.com/alecthomas/kong"
 	"google.golang.org/api/docs/v1"
 
 	"github.com/steipete/gogcli/internal/outfmt"
@@ -24,11 +25,20 @@ type DocsCatCmd struct {
 	Numbered bool   `name:"numbered" short:"N" help:"Prefix each paragraph with its number"`
 }
 
-func (c *DocsCatCmd) Run(ctx context.Context, flags *RootFlags) error {
+func (c *DocsCatCmd) Run(ctx context.Context, kctx *kong.Context, flags *RootFlags) error {
 	id := strings.TrimSpace(c.DocID)
 	if id == "" {
 		return usage("empty docId")
 	}
+	tabProvided := flagProvided(kctx, "tab") || c.Tab != ""
+	tab := strings.TrimSpace(c.Tab)
+	if tabProvided && tab == "" {
+		return usage("--tab cannot be empty")
+	}
+	c.Tab = tab
+	if c.Tab != "" && c.AllTabs {
+		return usage("--tab and --all-tabs cannot be used together")
+	}
 
 	svc, err := requireDocsService(ctx, flags)
 	if err != nil {
diff --git a/internal/cmd/docs_validation_more_test.go b/internal/cmd/docs_validation_more_test.go
index faf14f9b8..c7f40cb98 100644
--- a/internal/cmd/docs_validation_more_test.go
+++ b/internal/cmd/docs_validation_more_test.go
@@ -68,7 +68,7 @@ func TestDocsCreateCat_ValidationErrors(t *testing.T) {
 	if err := (&DocsCreateCmd{}).Run(ctx, flags); err == nil {
 		t.Fatalf("expected missing title error")
 	}
-	if err := (&DocsCatCmd{}).Run(ctx, flags); err == nil {
+	if err := (&DocsCatCmd{}).Run(ctx, nil, flags); err == nil {
 		t.Fatalf("expected missing docId error")
 	}
 }
@@ -113,7 +113,7 @@ func TestDocsCat_JSON_EmptyDoc(t *testing.T) {
 	ctx := withDocsTestService(newCmdRuntimeJSONOutputContext(t, &output, io.Discard), svc)
 	flags := &RootFlags{Account: "a@b.com"}
 
-	if err := (&DocsCatCmd{DocID: "doc1"}).Run(ctx, flags); err != nil {
+	if err := (&DocsCatCmd{DocID: "doc1"}).Run(ctx, nil, flags); err != nil {
 		t.Fatalf("cat: %v", err)
 	}
 	if !strings.Contains(output.String(), "\"text\"") {
diff --git a/internal/cmd/mcp_test.go b/internal/cmd/mcp_test.go
index 06b800229..5f953877d 100644
--- a/internal/cmd/mcp_test.go
+++ b/internal/cmd/mcp_test.go
@@ -241,6 +241,30 @@ func TestMCPDocsWriteRejectsNeitherAppendNorReplace(t *testing.T) {
 	}
 }
 
+func TestMCPDocsGetRejectsTabWithAllTabs(t *testing.T) {
+	tool := findMCPTool(t, "docs_get")
+	_, err := tool.BuildArgs(mcp.CallToolRequest{Params: mcp.CallToolParams{
+		Arguments: map[string]any{
+			"document_id": "doc1",
+			"tab":         "Overview",
+			"all_tabs":    true,
+		},
+	}})
+	if err == nil || !strings.Contains(err.Error(), "mutually exclusive") {
+		t.Fatalf("expected tab/all_tabs error, got %v", err)
+	}
+
+	_, err = tool.BuildArgs(mcp.CallToolRequest{Params: mcp.CallToolParams{
+		Arguments: map[string]any{
+			"document_id": "doc1",
+			"tab":         "",
+		},
+	}})
+	if err == nil || !strings.Contains(err.Error(), "tab cannot be empty") {
+		t.Fatalf("expected empty tab error, got %v", err)
+	}
+}
+
 func TestMCPSheetsUpdateRejectsFileExpansion(t *testing.T) {
 	tool := findMCPTool(t, "sheets_update_range")
 	_, err := tool.BuildArgs(mcp.CallToolRequest{Params: mcp.CallToolParams{
diff --git a/internal/cmd/mcp_tools.go b/internal/cmd/mcp_tools.go
index d3f4a8c92..6ace23d44 100644
--- a/internal/cmd/mcp_tools.go
+++ b/internal/cmd/mcp_tools.go
@@ -174,10 +174,19 @@ func mcpDocsGetTool() mcpToolSpec {
 				return nil, err
 			}
 			args := []string{"docs", "cat", "--max-bytes", strconv.Itoa(clampMCPInt(req.GetInt("max_bytes", 2000000), 0, 20_000_000))}
-			if tab := strings.TrimSpace(req.GetString("tab", "")); tab != "" {
+			tab := strings.TrimSpace(req.GetString("tab", ""))
+			_, tabProvided := req.GetArguments()["tab"]
+			if tabProvided && tab == "" {
+				return nil, fmt.Errorf("tab cannot be empty")
+			}
+			allTabs := req.GetBool("all_tabs", false)
+			if tab != "" && allTabs {
+				return nil, fmt.Errorf("tab and all_tabs are mutually exclusive")
+			}
+			if tab != "" {
 				args = append(args, "--tab", tab)
 			}
-			if req.GetBool("all_tabs", false) {
+			if allTabs {
 				args = append(args, "--all-tabs")
 			}
 			return append(args, "--", docID), nil