Claude Code Review MCP

Instructions

Implementation Reference

• src/index.ts:56-94 (handler)

  Primary asynchronous handler for the 'perform_code_review' tool, orchestrating git diff retrieval, LLM prompting, review generation, and error handling.

  async (params: CodeReviewToolParams) => {
    try {
      console.error(
        `[MCP Server Tool] Received 'perform_code_review' request. Target: ${params.target}, Provider: ${params.llmProvider}, Model: ${params.modelName}`
      );
  
      // Step 1: Get the diff from git
      const diffResult = await getGitDiffForReview(params);
      if (diffResult.noChanges) {
        return {
          content: [
            { type: "text", text: "No changes detected for review." },
          ],
        };
      }
  
      // Step 2: Prepare LLM prompt and get the review
      const reviewResult = await generateLLMReview(params, diffResult.diff);
  
      return {
        content: [{ type: "text", text: reviewResult }],
        isError: false, // Explicitly set isError
      };
    } catch (error: any) {
      console.error(
        "[MCP Server Tool] Error in 'perform_code_review' tool:",
        error.stack || error.message
      );
      return {
        isError: true,
        content: [
          {
            type: "text",
            text: `Error performing code review: ${error.message}`,
          },
        ],
      };
    }
  }

• src/config.ts:40-84 (schema)

  Zod schema (CodeReviewToolParamsSchema) defining and validating input parameters for the perform_code_review tool.

  export const CodeReviewToolParamsSchema = z.object({
    target: ReviewTargetEnum.describe(
      "The git target to review (e.g., 'staged', 'HEAD', or 'branch_diff')."
    ),
    taskDescription: z
      .string()
      .min(1)
      .describe(
        "Description of the task/feature/bugfix that led to these code changes."
      ),
    llmProvider: LLMProviderEnum.describe(
      "The LLM provider to use (google, openai, anthropic)."
    ),
    modelName: z
      .string()
      .min(1)
      .describe(
        "The specific model name from the provider (e.g., 'gemini-2.5-pro-preview-05-06', 'o4-mini', 'claude-3-7-sonnet-20250219')."
      ),
    reviewFocus: z
      .string()
      .optional()
      .describe(
        "Specific areas or aspects to focus the review on (e.g., 'security vulnerabilities', 'performance optimizations', 'adherence to SOLID principles')."
      ),
    projectContext: z
      .string()
      .optional()
      .describe(
        "General context about the project, its architecture, or coding standards."
      ),
    diffBase: z
      .string()
      .optional()
      .describe(
        "For 'branch_diff' target, the base branch or commit SHA to compare against (e.g., 'main', 'develop', 'specific-commit-sha'). Required if target is 'branch_diff'."
      ),
    maxTokens: z
      .number()
      .positive()
      .optional()
      .describe(
        "Maximum number of tokens to use for the LLM response. Defaults to 32000 if not specified."
      ),
  });

• src/index.ts:51-96 (registration)

  Registers the 'perform_code_review' tool with the MCP server using server.tool(), providing name, description, input schema, and handler.

  function registerCodeReviewTool(server: McpServer) {
    server.tool(
      "perform_code_review",
      "Performs a code review using a specified LLM on git changes. Requires being run from the root of a git repository.",
      CodeReviewToolParamsSchema.shape,
      async (params: CodeReviewToolParams) => {
        try {
          console.error(
            `[MCP Server Tool] Received 'perform_code_review' request. Target: ${params.target}, Provider: ${params.llmProvider}, Model: ${params.modelName}`
          );
  
          // Step 1: Get the diff from git
          const diffResult = await getGitDiffForReview(params);
          if (diffResult.noChanges) {
            return {
              content: [
                { type: "text", text: "No changes detected for review." },
              ],
            };
          }
  
          // Step 2: Prepare LLM prompt and get the review
          const reviewResult = await generateLLMReview(params, diffResult.diff);
  
          return {
            content: [{ type: "text", text: reviewResult }],
            isError: false, // Explicitly set isError
          };
        } catch (error: any) {
          console.error(
            "[MCP Server Tool] Error in 'perform_code_review' tool:",
            error.stack || error.message
          );
          return {
            isError: true,
            content: [
              {
                type: "text",
                text: `Error performing code review: ${error.message}`,
              },
            ],
          };
        }
      }
    );
  }

• src/git-utils.ts:15-122 (helper)

  Helper function getGitDiff that retrieves git diff for specified target, called from tool handler.

  export function getGitDiff(target: ReviewTarget, baseBranch?: string): string {
    const execOptions: ExecSyncOptionsWithStringEncoding = {
      encoding: "utf8",
      maxBuffer: 20 * 1024 * 1024, // Increased to 20MB buffer
      stdio: ["pipe", "pipe", "pipe"], // pipe stderr to catch git errors
    };
  
    let command: string = "";
  
    try {
      // Verify it's a git repository first
      execSync("git rev-parse --is-inside-work-tree", {
        ...execOptions,
        stdio: "ignore",
      });
    } catch (error) {
      console.error(
        "[MCP Server Git] Current directory is not a git repository or git is not found."
      );
      throw new Error(
        "Execution directory is not a git repository or git command is not available. Please run from a git project root."
      );
    }
  
    try {
      switch (target) {
        case "staged":
          command = "git diff --staged --patch-with-raw --unified=10"; // More context
          break;
        case "HEAD":
          command = "git diff HEAD --patch-with-raw --unified=10";
          break;
        case "branch_diff":
          if (!baseBranch || baseBranch.trim() === "") {
            throw new Error(
              "Base branch/commit is required for 'branch_diff' target and cannot be empty."
            );
          }
          // Sanitize baseBranch to prevent command injection
          // Only allow alphanumeric characters, underscore, dash, dot, and forward slash
          const sanitizedBaseBranch = baseBranch.replace(
            /[^a-zA-Z0-9_.\-/]/g,
            ""
          );
          if (sanitizedBaseBranch !== baseBranch) {
            throw new Error(
              `Invalid characters in base branch name. Only alphanumeric characters, underscore, dash, dot, and forward slash are allowed. Received: "${baseBranch}"`
            );
          }
          // Fetch the base branch to ensure the diff is against the latest version of it
          // Note: This assumes the remote is named 'origin'
          const fetchCommand = `git fetch origin ${sanitizedBaseBranch}:${sanitizedBaseBranch} --no-tags --quiet`;
          try {
            execSync(fetchCommand, execOptions);
          } catch (fetchError: any) {
            // Log a warning but proceed; the branch might be local or already up-to-date
            console.warn(
              `[MCP Server Git] Warning during 'git fetch' for base branch '${sanitizedBaseBranch}': ${fetchError.message}. Diff will proceed with local state.`
            );
          }
          command = `git diff ${sanitizedBaseBranch}...HEAD --patch-with-raw --unified=10`;
          break;
        default:
          // This case should ideally be caught by Zod validation on parameters
          throw new Error(`Unsupported git diff target: ${target}`);
      }
  
      // Only log the command if in debug mode
      if (isDebugMode()) {
        console.log(`[MCP Server Git] Executing: ${command}`);
      }
      
      // Execute the command (execOptions has encoding:'utf8' so the result should already be a string)
      const diffOutput = execSync(command, execOptions);
      
      // Ensure we always have a string to work with
      // This is for type safety and to handle any unexpected Buffer return types
      const diffString = Buffer.isBuffer(diffOutput) ? diffOutput.toString('utf8') : String(diffOutput);
      
      if (!diffString.trim()) {
        return "No changes found for the specified target.";
      }
      return diffString;
    } catch (error: any) {
      const errorMessage =
        error.stderr?.toString().trim() || error.message || "Unknown git error";
      console.error(
        `[MCP Server Git] Error getting git diff for target "${target}" (base: ${
          baseBranch || "N/A"
        }):`
      );
      console.error(`[MCP Server Git] Command: ${command || "N/A"}`);
      
      // Only log the full error details in debug mode
      if (isDebugMode()) {
        console.error(
          `[MCP Server Git] Stderr: ${error.stderr?.toString().trim()}`
        );
        console.error(
          `[MCP Server Git] Stdout: ${error.stdout?.toString().trim()}`
        );
      }
      
      throw new Error(
        `Failed to get git diff. Git error: ${errorMessage}. Ensure you are in a git repository and the target/base is valid.`
      );
    }
  }

• src/llm-service.ts:34-135 (helper)

  Core helper getLLMReview for calling LLM providers to generate code review text based on prompt and diff.

  export async function getLLMReview<T extends LLMProvider>(
    provider: T,
    modelName: ModelName<T>,
    systemPrompt: string,
    userMessages: CoreMessage[],
    maxTokens: number = 32000
  ): Promise<string> {
    // Make sure we have the API key
    const apiKey = getApiKey(provider);
    if (!apiKey) {
      throw new Error(
        `API key for ${provider} is not configured. Please set the appropriate environment variable.`
      );
    }
  
    // Create the LLM client with proper provider configuration
    let llmClient;
    switch (provider) {
      case "google":
        // Create Google provider with explicit API key
        const googleAI = createGoogleGenerativeAI({
          apiKey,
        });
        llmClient = googleAI(modelName);
        break;
      case "openai":
        // Create OpenAI provider with explicit API key
        const openaiProvider = createOpenAI({
          apiKey,
        });
        llmClient = openaiProvider(modelName);
        break;
      case "anthropic":
        // Create Anthropic provider with explicit API key
        const anthropicProvider = createAnthropic({
          apiKey,
        });
        llmClient = anthropicProvider(modelName);
        break;
      default:
        throw new Error(`Unsupported LLM provider: ${provider}`);
    }
  
    try {
      if (isDebugMode()) {
        console.log(
          `[MCP Server LLM] Requesting review from ${provider} model ${modelName} with max tokens ${maxTokens}.`
        );
      } else {
        console.log(
          `[MCP Server LLM] Requesting review from ${provider} model ${modelName}.`
        );
      }
      
      const { text, finishReason, usage, warnings } = await generateText({
        model: llmClient,
        system: systemPrompt,
        messages: userMessages,
        maxTokens: maxTokens, // Now configurable with default value
        temperature: 0.2, // Lower temperature for more deterministic and factual reviews
      });
  
      if (warnings && warnings.length > 0) {
        warnings.forEach((warning) =>
          console.warn(`[MCP Server LLM] Warning from ${provider}:`, warning)
        );
      }
      
      if (isDebugMode() && usage) {
        console.log(
          `[MCP Server LLM] Review received from ${provider}. Finish Reason: ${finishReason}, Tokens Used: Input=${usage.promptTokens}, Output=${usage.completionTokens}`
        );
      } else {
        console.log(
          `[MCP Server LLM] Review received from ${provider}.`
        );
      }
      
      return text;
    } catch (error: any) {
      console.error(
        `[MCP Server LLM] Error getting LLM review from ${provider} (${modelName}):`,
        error
      );
      let detailedMessage = error.message;
      if (error.cause) {
        detailedMessage += ` | Cause: ${JSON.stringify(error.cause)}`;
      }
      // Attempt to get more details from common API error structures
      if (error.response && error.response.data && error.response.data.error) {
        detailedMessage += ` | API Error: ${JSON.stringify(
          error.response.data.error
        )}`;
      } else if (error.error && error.error.message) {
        // Anthropic SDK style
        detailedMessage += ` | API Error: ${error.error.message}`;
      }
      throw new Error(
        `LLM API call failed for ${provider} (${modelName}): ${detailedMessage}`
      );
    }
  }