update unit test

.github/workflows/deploy_dev_docs.yaml

@@ -40,7 +40,7 @@ jobs:
       group: docs-deployment
       cancel-in-progress: false
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           fetch-depth: 0 # Fetch all history for .GitInfo and .Lastmod
 
@@ -56,7 +56,7 @@ jobs:
           node-version: "22"
 
       - name: Cache dependencies
-        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5
+        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

.github/workflows/deploy_previous_version_docs.yaml

@@ -30,14 +30,14 @@ jobs:
 
     steps:
       - name: Checkout main branch (for latest templates and theme)
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           ref: 'main'
           submodules: 'recursive'
           fetch-depth: 0
 
       - name: Checkout old content from tag into a temporary directory
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           ref: ${{ github.event.inputs.version_tag }}
           path: 'old_version_source' # Checkout into a temp subdir

.github/workflows/deploy_versioned_docs.yaml

@@ -30,7 +30,7 @@ jobs:
       cancel-in-progress: false
     steps:
       - name: Checkout Code at Tag
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           ref: ${{ github.event.release.tag_name }}
 

.github/workflows/docs_preview_clean.yaml

@@ -34,7 +34,7 @@ jobs:
       group: "preview-${{ github.event.number }}"
       cancel-in-progress: true
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           ref: versioned-gh-pages
 

.github/workflows/docs_preview_deploy.yaml

@@ -49,7 +49,7 @@ jobs:
       group: "preview-${{ github.event.number }}"
       cancel-in-progress: true
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
         with:
           # Checkout the PR's HEAD commit (supports forks).
           ref: ${{ github.event.pull_request.head.sha }}
@@ -67,7 +67,7 @@ jobs:
           node-version: "22"
 
       - name: Cache dependencies
-        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5
+        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

.github/workflows/link_checker_workflow.yaml

@@ -22,10 +22,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
 
       - name: Restore lychee cache
-        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5
+        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5
         with:
           path: .lycheecache
           key: cache-lychee-${{ github.sha }}

.github/workflows/publish-mcp.yml

@@ -29,7 +29,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
 
       - name: Wait for image in Artifact Registry
         shell: bash

docs/en/getting-started/quickstart/js/genkit/quickstart.js

@@ -53,7 +53,7 @@ export async function main() {
 
   for (const query of queries) {
     conversationHistory.push({ role: "user", content: [{ text: query }] });
-    let response = await ai.generate({
+    const response = await ai.generate({
       messages: conversationHistory,
       tools: tools,
     });

docs/en/how-to/invoke_tool.md

@@ -13,12 +13,12 @@ The `invoke` command allows you to invoke tools defined in your configuration di
 
 {{< notice tip >}}
 **Keep configurations minimal:** The `invoke` command initializes *all* resources (sources, tools, etc.) defined in your configuration files during execution. To ensure fast response times, consider using a minimal configuration file containing only the tools you need for the specific invocation.
-{{< /notice >}}
+{{< notice tip >}}
 
-## Before you begin
+## Prerequisites
 
-1. Make sure you have the `toolbox` binary installed or built.
+- You have the `toolbox` binary installed or built.
-2. Make sure you have a valid tool configuration file (e.g., `tools.yaml`).
+- You have a valid tool configuration file (e.g., `tools.yaml`).
 
 ## Basic Usage
 

docs/en/resources/tools/cloudloggingadmin/_index.md

@@ -1,8 +0,0 @@
----
-title: "Cloud Logging Admin"
-linkTitle: "Cloud Logging Admin"
-type: docs
-weight: 1
-description: > 
-  Tools that work with Cloud Logging Admin Sources.
----

internal/server/api.go

@@ -19,7 +19,6 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
-	"strings"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
@@ -234,10 +233,11 @@ func toolInvokeHandler(s *Server, w http.ResponseWriter, r *http.Request) {
 
 	params, err := parameters.ParseParams(tool.GetParameters(), data, claimsFromAuth)
 	if err != nil {
-		// If auth error, return 401
+		// If auth error, return 401 or 403
-		if errors.Is(err, util.ErrUnauthorized) {
+		var clientServerErr *util.ClientServerError
+		if errors.As(err, &clientServerErr) && (clientServerErr.Code == http.StatusUnauthorized || clientServerErr.Code == http.StatusForbidden) {
 			s.logger.DebugContext(ctx, fmt.Sprintf("error parsing authenticated parameters from ID token: %s", err))
-			_ = render.Render(w, r, newErrResponse(err, http.StatusUnauthorized))
+			_ = render.Render(w, r, newErrResponse(err, clientServerErr.Code))
 			return
 		}
 		err = fmt.Errorf("provided parameters were invalid: %w", err)
@@ -259,34 +259,49 @@ func toolInvokeHandler(s *Server, w http.ResponseWriter, r *http.Request) {
 
 	// Determine what error to return to the users.
 	if err != nil {
-		errStr := err.Error()
+		var tbErr util.ToolboxError
-		var statusCode int
 
-		// Upstream API auth error propagation
+		if errors.As(err, &tbErr) {
-		switch {
+			switch tbErr.Category() {
-		case strings.Contains(errStr, "Error 401"):
+			case util.CategoryAgent:
-			statusCode = http.StatusUnauthorized
+				// Agent Errors -> 200 OK
-		case strings.Contains(errStr, "Error 403"):
+				s.logger.DebugContext(ctx, fmt.Sprintf("Tool invocation agent error: %v", err))
-			statusCode = http.StatusForbidden
+				_ = render.Render(w, r, newErrResponse(err, http.StatusOK))
-		}
+				return
 
-		if statusCode == http.StatusUnauthorized || statusCode == http.StatusForbidden {
+			case util.CategoryServer:
-			if clientAuth {
+				// Server Errors -> Check the specific code inside
-				// Propagate the original 401/403 error.
+				var clientServerErr *util.ClientServerError
-				s.logger.DebugContext(ctx, fmt.Sprintf("error invoking tool. Client credentials lack authorization to the source: %v", err))
+				statusCode := http.StatusInternalServerError // Default to 500
+
+				if errors.As(err, &clientServerErr) {
+					if clientServerErr.Code != 0 {
+						statusCode = clientServerErr.Code
+					}
+				}
+
+				// Process auth error
+				if statusCode == http.StatusUnauthorized || statusCode == http.StatusForbidden {
+					if clientAuth {
+						// Token error, pass through 401/403
+						s.logger.DebugContext(ctx, fmt.Sprintf("Client credentials lack authorization: %v", err))
+						_ = render.Render(w, r, newErrResponse(err, statusCode))
+						return
+					}
+					// ADC/Config error, return 500
+					statusCode = http.StatusInternalServerError
+				}
+
+				s.logger.ErrorContext(ctx, fmt.Sprintf("Tool invocation server error: %v", err))
 				_ = render.Render(w, r, newErrResponse(err, statusCode))
 				return
 			}
-			// ADC lacking permission or credentials configuration error.
+		} else {
-			internalErr := fmt.Errorf("unexpected auth error occured during Tool invocation: %w", err)
+			// Unknown error -> 500
-			s.logger.ErrorContext(ctx, internalErr.Error())
+			s.logger.ErrorContext(ctx, fmt.Sprintf("Tool invocation unknown error: %v", err))
-			_ = render.Render(w, r, newErrResponse(internalErr, http.StatusInternalServerError))
+			_ = render.Render(w, r, newErrResponse(err, http.StatusInternalServerError))
 			return
 		}
-		err = fmt.Errorf("error while invoking tool: %w", err)
-		s.logger.DebugContext(ctx, err.Error())
-		_ = render.Render(w, r, newErrResponse(err, http.StatusBadRequest))
-		return
 	}
 
 	resMarshal, err := json.Marshal(res)

internal/server/mcp.go

@@ -23,7 +23,6 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"strings"
 	"sync"
 	"time"
 
@@ -444,15 +443,12 @@ func httpHandler(s *Server, w http.ResponseWriter, r *http.Request) {
 		code := rpcResponse.Error.Code
 		switch code {
 		case jsonrpc.INTERNAL_ERROR:
+			// Map Internal RPC Error (-32603) to HTTP 500
 			w.WriteHeader(http.StatusInternalServerError)
 		case jsonrpc.INVALID_REQUEST:
-			errStr := err.Error()
+			var clientServerErr *util.ClientServerError
-			if errors.Is(err, util.ErrUnauthorized) {
+			if errors.As(err, &clientServerErr) {
-				w.WriteHeader(http.StatusUnauthorized)
+				w.WriteHeader(clientServerErr.Code)
-			} else if strings.Contains(errStr, "Error 401") {
-				w.WriteHeader(http.StatusUnauthorized)
-			} else if strings.Contains(errStr, "Error 403") {
-				w.WriteHeader(http.StatusForbidden)
 			}
 		}
 	}

internal/server/mcp/v20241105/method.go

@@ -21,7 +21,6 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
-	"strings"
 
 	"github.com/googleapis/genai-toolbox/internal/prompts"
 	"github.com/googleapis/genai-toolbox/internal/server/mcp/jsonrpc"
@@ -124,7 +123,12 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	}
 	if clientAuth {
 		if accessToken == "" {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, "missing access token in the 'Authorization' header", nil), util.ErrUnauthorized
+			errMsg := "missing access token in the 'Authorization' header"
+			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, errMsg, nil), util.NewClientServerError(
+				errMsg,
+				http.StatusUnauthorized,
+				nil,
+			)
 		}
 	}
 
@@ -172,7 +176,11 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// Check if any of the specified auth services is verified
 	isAuthorized := tool.Authorized(verifiedAuthServices)
 	if !isAuthorized {
-		err = fmt.Errorf("unauthorized Tool call: Please make sure your specify correct auth headers: %w", util.ErrUnauthorized)
+		err = util.NewClientServerError(
+			"unauthorized Tool call: Please make sure you specify correct auth headers",
+			http.StatusUnauthorized,
+			nil,
+		)
 		return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
 	}
 	logger.DebugContext(ctx, "tool invocation authorized")
@@ -194,30 +202,44 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// run tool invocation and generate response.
 	results, err := tool.Invoke(ctx, resourceMgr, params, accessToken)
 	if err != nil {
-		errStr := err.Error()
+		var tbErr util.ToolboxError
-		// Missing authService tokens.
+
-		if errors.Is(err, util.ErrUnauthorized) {
+		if errors.As(err, &tbErr) {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+			switch tbErr.Category() {
-		}
+			case util.CategoryAgent:
-		// Upstream auth error
+				// MCP - Tool execution error
-		if strings.Contains(errStr, "Error 401") || strings.Contains(errStr, "Error 403") {
+				// Return SUCCESS but with IsError: true
-			if clientAuth {
+				text := TextContent{
-				// Error with client credentials should pass down to the client
+					Type: "text",
-				return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+					Text: err.Error(),
+				}
+				return jsonrpc.JSONRPCResponse{
+					Jsonrpc: jsonrpc.JSONRPC_VERSION,
+					Id:      id,
+					Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
+				}, nil
+
+			case util.CategoryServer:
+				// MCP Spec - Protocol error
+				// Return JSON-RPC ERROR
+				var clientServerErr *util.ClientServerError
+				rpcCode := jsonrpc.INTERNAL_ERROR // Default to Internal Error (-32603)
+
+				if errors.As(err, &clientServerErr) {
+					if clientServerErr.Code == http.StatusUnauthorized || clientServerErr.Code == http.StatusForbidden {
+						if clientAuth {
+							rpcCode = jsonrpc.INVALID_REQUEST
+						} else {
+							rpcCode = jsonrpc.INTERNAL_ERROR
+						}
+					}
+				}
+				return jsonrpc.NewError(id, rpcCode, err.Error(), nil), err
 			}
-			// Auth error with ADC should raise internal 500 error
+		} else {
+			// Unknown error -> 500
 			return jsonrpc.NewError(id, jsonrpc.INTERNAL_ERROR, err.Error(), nil), err
 		}
-
-		text := TextContent{
-			Type: "text",
-			Text: err.Error(),
-		}
-		return jsonrpc.JSONRPCResponse{
-			Jsonrpc: jsonrpc.JSONRPC_VERSION,
-			Id:      id,
-			Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
-		}, nil
 	}
 
 	content := make([]TextContent, 0)

internal/server/mcp/v20250326/method.go

@@ -21,7 +21,6 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
-	"strings"
 
 	"github.com/googleapis/genai-toolbox/internal/prompts"
 	"github.com/googleapis/genai-toolbox/internal/server/mcp/jsonrpc"
@@ -124,7 +123,12 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	}
 	if clientAuth {
 		if accessToken == "" {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, "missing access token in the 'Authorization' header", nil), util.ErrUnauthorized
+			errMsg := "missing access token in the 'Authorization' header"
+			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, errMsg, nil), util.NewClientServerError(
+				errMsg,
+				http.StatusUnauthorized,
+				nil,
+			)
 		}
 	}
 
@@ -172,7 +176,11 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// Check if any of the specified auth services is verified
 	isAuthorized := tool.Authorized(verifiedAuthServices)
 	if !isAuthorized {
-		err = fmt.Errorf("unauthorized Tool call: Please make sure your specify correct auth headers: %w", util.ErrUnauthorized)
+		err = util.NewClientServerError(
+			"unauthorized Tool call: Please make sure you specify correct auth headers",
+			http.StatusUnauthorized,
+			nil,
+		)
 		return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
 	}
 	logger.DebugContext(ctx, "tool invocation authorized")
@@ -194,31 +202,45 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// run tool invocation and generate response.
 	results, err := tool.Invoke(ctx, resourceMgr, params, accessToken)
 	if err != nil {
-		errStr := err.Error()
+		var tbErr util.ToolboxError
-		// Missing authService tokens.
+
-		if errors.Is(err, util.ErrUnauthorized) {
+		if errors.As(err, &tbErr) {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+			switch tbErr.Category() {
-		}
+			case util.CategoryAgent:
-		// Upstream auth error
+				// MCP - Tool execution error
-		if strings.Contains(errStr, "Error 401") || strings.Contains(errStr, "Error 403") {
+				// Return SUCCESS but with IsError: true
-			if clientAuth {
+				text := TextContent{
-				// Error with client credentials should pass down to the client
+					Type: "text",
-				return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+					Text: err.Error(),
+				}
+				return jsonrpc.JSONRPCResponse{
+					Jsonrpc: jsonrpc.JSONRPC_VERSION,
+					Id:      id,
+					Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
+				}, nil
+
+			case util.CategoryServer:
+				// MCP Spec - Protocol error
+				// Return JSON-RPC ERROR
+				var clientServerErr *util.ClientServerError
+				rpcCode := jsonrpc.INTERNAL_ERROR // Default to Internal Error (-32603)
+
+				if errors.As(err, &clientServerErr) {
+					if clientServerErr.Code == http.StatusUnauthorized || clientServerErr.Code == http.StatusForbidden {
+						if clientAuth {
+							rpcCode = jsonrpc.INVALID_REQUEST
+						} else {
+							rpcCode = jsonrpc.INTERNAL_ERROR
+						}
+					}
+				}
+				return jsonrpc.NewError(id, rpcCode, err.Error(), nil), err
 			}
-			// Auth error with ADC should raise internal 500 error
+		} else {
+			// Unknown error -> 500
 			return jsonrpc.NewError(id, jsonrpc.INTERNAL_ERROR, err.Error(), nil), err
 		}
-		text := TextContent{
-			Type: "text",
-			Text: err.Error(),
-		}
-		return jsonrpc.JSONRPCResponse{
-			Jsonrpc: jsonrpc.JSONRPC_VERSION,
-			Id:      id,
-			Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
-		}, nil
 	}
-
 	content := make([]TextContent, 0)
 
 	sliceRes, ok := results.([]any)

internal/server/mcp/v20250618/method.go

@@ -21,7 +21,6 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
-	"strings"
 
 	"github.com/googleapis/genai-toolbox/internal/prompts"
 	"github.com/googleapis/genai-toolbox/internal/server/mcp/jsonrpc"
@@ -117,7 +116,12 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	}
 	if clientAuth {
 		if accessToken == "" {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, "missing access token in the 'Authorization' header", nil), util.ErrUnauthorized
+			errMsg := "missing access token in the 'Authorization' header"
+			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, errMsg, nil), util.NewClientServerError(
+				errMsg,
+				http.StatusUnauthorized,
+				nil,
+			)
 		}
 	}
 
@@ -165,7 +169,11 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// Check if any of the specified auth services is verified
 	isAuthorized := tool.Authorized(verifiedAuthServices)
 	if !isAuthorized {
-		err = fmt.Errorf("unauthorized Tool call: Please make sure your specify correct auth headers: %w", util.ErrUnauthorized)
+		err = util.NewClientServerError(
+			"unauthorized Tool call: Please make sure you specify correct auth headers",
+			http.StatusUnauthorized,
+			nil,
+		)
 		return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
 	}
 	logger.DebugContext(ctx, "tool invocation authorized")
@@ -187,29 +195,44 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// run tool invocation and generate response.
 	results, err := tool.Invoke(ctx, resourceMgr, params, accessToken)
 	if err != nil {
-		errStr := err.Error()
+		var tbErr util.ToolboxError
-		// Missing authService tokens.
+
-		if errors.Is(err, util.ErrUnauthorized) {
+		if errors.As(err, &tbErr) {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+			switch tbErr.Category() {
-		}
+			case util.CategoryAgent:
-		// Upstream auth error
+				// MCP - Tool execution error
-		if strings.Contains(errStr, "Error 401") || strings.Contains(errStr, "Error 403") {
+				// Return SUCCESS but with IsError: true
-			if clientAuth {
+				text := TextContent{
-				// Error with client credentials should pass down to the client
+					Type: "text",
-				return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+					Text: err.Error(),
+				}
+				return jsonrpc.JSONRPCResponse{
+					Jsonrpc: jsonrpc.JSONRPC_VERSION,
+					Id:      id,
+					Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
+				}, nil
+
+			case util.CategoryServer:
+				// MCP Spec - Protocol error
+				// Return JSON-RPC ERROR
+				var clientServerErr *util.ClientServerError
+				rpcCode := jsonrpc.INTERNAL_ERROR // Default to Internal Error (-32603)
+
+				if errors.As(err, &clientServerErr) {
+					if clientServerErr.Code == http.StatusUnauthorized || clientServerErr.Code == http.StatusForbidden {
+						if clientAuth {
+							rpcCode = jsonrpc.INVALID_REQUEST
+						} else {
+							rpcCode = jsonrpc.INTERNAL_ERROR
+						}
+					}
+				}
+				return jsonrpc.NewError(id, rpcCode, err.Error(), nil), err
 			}
-			// Auth error with ADC should raise internal 500 error
+		} else {
+			// Unknown error -> 500
 			return jsonrpc.NewError(id, jsonrpc.INTERNAL_ERROR, err.Error(), nil), err
 		}
-		text := TextContent{
-			Type: "text",
-			Text: err.Error(),
-		}
-		return jsonrpc.JSONRPCResponse{
-			Jsonrpc: jsonrpc.JSONRPC_VERSION,
-			Id:      id,
-			Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
-		}, nil
 	}
 
 	content := make([]TextContent, 0)

internal/server/mcp/v20251125/method.go

@@ -21,7 +21,6 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
-	"strings"
 
 	"github.com/googleapis/genai-toolbox/internal/prompts"
 	"github.com/googleapis/genai-toolbox/internal/server/mcp/jsonrpc"
@@ -117,7 +116,12 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	}
 	if clientAuth {
 		if accessToken == "" {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, "missing access token in the 'Authorization' header", nil), util.ErrUnauthorized
+			errMsg := "missing access token in the 'Authorization' header"
+			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, errMsg, nil), util.NewClientServerError(
+				errMsg,
+				http.StatusUnauthorized,
+				nil,
+			)
 		}
 	}
 
@@ -165,7 +169,11 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// Check if any of the specified auth services is verified
 	isAuthorized := tool.Authorized(verifiedAuthServices)
 	if !isAuthorized {
-		err = fmt.Errorf("unauthorized Tool call: Please make sure your specify correct auth headers: %w", util.ErrUnauthorized)
+		err = util.NewClientServerError(
+			"unauthorized Tool call: Please make sure you specify correct auth headers",
+			http.StatusUnauthorized,
+			nil,
+		)
 		return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
 	}
 	logger.DebugContext(ctx, "tool invocation authorized")
@@ -187,29 +195,44 @@ func toolsCallHandler(ctx context.Context, id jsonrpc.RequestId, resourceMgr *re
 	// run tool invocation and generate response.
 	results, err := tool.Invoke(ctx, resourceMgr, params, accessToken)
 	if err != nil {
-		errStr := err.Error()
+		var tbErr util.ToolboxError
-		// Missing authService tokens.
+
-		if errors.Is(err, util.ErrUnauthorized) {
+		if errors.As(err, &tbErr) {
-			return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+			switch tbErr.Category() {
-		}
+			case util.CategoryAgent:
-		// Upstream auth error
+				// MCP - Tool execution error
-		if strings.Contains(errStr, "Error 401") || strings.Contains(errStr, "Error 403") {
+				// Return SUCCESS but with IsError: true
-			if clientAuth {
+				text := TextContent{
-				// Error with client credentials should pass down to the client
+					Type: "text",
-				return jsonrpc.NewError(id, jsonrpc.INVALID_REQUEST, err.Error(), nil), err
+					Text: err.Error(),
+				}
+				return jsonrpc.JSONRPCResponse{
+					Jsonrpc: jsonrpc.JSONRPC_VERSION,
+					Id:      id,
+					Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
+				}, nil
+
+			case util.CategoryServer:
+				// MCP Spec - Protocol error
+				// Return JSON-RPC ERROR
+				var clientServerErr *util.ClientServerError
+				rpcCode := jsonrpc.INTERNAL_ERROR // Default to Internal Error (-32603)
+
+				if errors.As(err, &clientServerErr) {
+					if clientServerErr.Code == http.StatusUnauthorized || clientServerErr.Code == http.StatusForbidden {
+						if clientAuth {
+							rpcCode = jsonrpc.INVALID_REQUEST
+						} else {
+							rpcCode = jsonrpc.INTERNAL_ERROR
+						}
+					}
+				}
+				return jsonrpc.NewError(id, rpcCode, err.Error(), nil), err
 			}
-			// Auth error with ADC should raise internal 500 error
+		} else {
+			// Unknown error -> 500
 			return jsonrpc.NewError(id, jsonrpc.INTERNAL_ERROR, err.Error(), nil), err
 		}
-		text := TextContent{
-			Type: "text",
-			Text: err.Error(),
-		}
-		return jsonrpc.JSONRPCResponse{
-			Jsonrpc: jsonrpc.JSONRPC_VERSION,
-			Id:      id,
-			Result:  CallToolResult{Content: []TextContent{text}, IsError: true},
-		}, nil
 	}
 
 	content := make([]TextContent, 0)

internal/server/mcp_test.go

@@ -231,7 +231,7 @@ func TestMcpEndpointWithoutInitialized(t *testing.T) {
 				"id":      "tools-call-tool4",
 				"error": map[string]any{
 					"code":    -32600.0,
-					"message": "unauthorized Tool call: Please make sure your specify correct auth headers: unauthorized",
+					"message": "unauthorized Tool call: Please make sure you specify correct auth headers: <nil>",
 				},
 			},
 		},
@@ -834,7 +834,7 @@ func TestMcpEndpoint(t *testing.T) {
 						"id":      "tools-call-tool4",
 						"error": map[string]any{
 							"code":    -32600.0,
-							"message": "unauthorized Tool call: Please make sure your specify correct auth headers: unauthorized",
+							"message": "unauthorized Tool call: Please make sure you specify correct auth headers: <nil>",
 						},
 					},
 				},

internal/tools/bigquery/bigqueryconversationalanalytics/bigqueryconversationalanalytics.go

@@ -184,7 +184,7 @@ func (t Tool) Invoke(ctx context.Context, resourceMgr tools.SourceProvider, para
 	if source.UseClientAuthorization() {
 		// Use client-side access token
 		if accessToken == "" {
-			return nil, fmt.Errorf("tool is configured for client OAuth but no token was provided in the request header: %w", util.ErrUnauthorized)
+			return nil, util.NewClientServerError("tool is configured for client OAuth but no token was provided in the request header", http.StatusUnauthorized, nil)
 		}
 		tokenStr, err = accessToken.ParseBearerToken()
 		if err != nil {

internal/tools/tools.go

@@ -17,6 +17,7 @@ package tools
 import (
 	"context"
 	"fmt"
+	"net/http"
 	"slices"
 	"strings"
 
@@ -80,7 +81,7 @@ type AccessToken string
 func (token AccessToken) ParseBearerToken() (string, error) {
 	headerParts := strings.Split(string(token), " ")
 	if len(headerParts) != 2 || strings.ToLower(headerParts[0]) != "bearer" {
-		return "", fmt.Errorf("authorization header must be in the format 'Bearer <token>': %w", util.ErrUnauthorized)
+		return "", util.NewClientServerError("authorization header must be in the format 'Bearer <token>'", http.StatusUnauthorized, nil)
 	}
 	return headerParts[1], nil
 }

internal/util/errors.go

@@ -0,0 +1,61 @@
+// Copyright 2026 Google LLC
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package util
+
+import "fmt"
+
+type ErrorCategory string
+
+const (
+	CategoryAgent  ErrorCategory = "AGENT_ERROR"
+	CategoryServer ErrorCategory = "SERVER_ERROR"
+)
+
+// ToolboxError is the interface all custom errors must satisfy
+type ToolboxError interface {
+	error
+	Category() ErrorCategory
+}
+
+// Agent Errors return 200 to the sender
+type AgentError struct {
+	Msg   string
+	Cause error
+}
+
+func (e *AgentError) Error() string { return e.Msg }
+
+func (e *AgentError) Category() ErrorCategory { return CategoryAgent }
+
+func (e *AgentError) Unwrap() error { return e.Cause }
+
+func NewAgentError(msg string, cause error) *AgentError {
+	return &AgentError{Msg: msg, Cause: cause}
+}
+
+// ClientServerError returns 4XX/5XX error code
+type ClientServerError struct {
+	Msg   string
+	Code  int
+	Cause error
+}
+
+func (e *ClientServerError) Error() string { return fmt.Sprintf("%s: %v", e.Msg, e.Cause) }
+
+func (e *ClientServerError) Category() ErrorCategory { return CategoryServer }
+
+func (e *ClientServerError) Unwrap() error { return e.Cause }
+
+func NewClientServerError(msg string, code int, cause error) *ClientServerError {
+	return &ClientServerError{Msg: msg, Code: code, Cause: cause}
+}

internal/util/parameters/parameters.go

@@ -19,6 +19,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"net/http"
 	"reflect"
 	"regexp"
 	"slices"
@@ -118,7 +119,7 @@ func parseFromAuthService(paramAuthServices []ParamAuthService, claimsMap map[st
 		}
 		return v, nil
 	}
-	return nil, fmt.Errorf("missing or invalid authentication header: %w", util.ErrUnauthorized)
+	return nil, util.NewClientServerError("missing or invalid authentication header", http.StatusUnauthorized, nil)
 }
 
 // CheckParamRequired checks if a parameter is required based on the required and default field.

internal/util/util.go

@@ -17,7 +17,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -188,5 +187,3 @@ func InstrumentationFromContext(ctx context.Context) (*telemetry.Instrumentation
 	}
 	return nil, fmt.Errorf("unable to retrieve instrumentation")
 }
-
-var ErrUnauthorized = errors.New("unauthorized")