Loki MCP Server

Implementation Reference

• src/index.ts:180-200 (handler)

  MCP tool handler for "get_labels". Logs execution, calls lokiClient.getLabels(), returns result as text content or standardized error.

  server.tool("get_labels", {}, async (_args, extra) => {
    logger.debug("All labels query tool execution", { extra });
  
    try {
      const labelsJson = await lokiClient.getLabels();
  
      return {
        content: [
          {
            type: "text",
            text: labelsJson,
          },
        ],
      };
    } catch (error) {
      logger.error("Labels query tool execution error", { error });
  
      // Create standardized error response
      return createToolErrorResponse(error, "Error getting labels");
    }
  });

• src/utils/loki-client.ts:301-323 (helper)

  LokiClient.getLabels() public method: fetches labels via HTTP helper and returns JSON string {"labels": [...]}, with error handling.

  async getLabels(): Promise<string> {
    this.logger.debug("Retrieving label list");
    try {
      const labels = await this.getLabelsViaHttp();
      return JSON.stringify({ labels });
    } catch (error: unknown) {
      const errorMsg = error instanceof Error ? error.message : String(error);
      this.logger.error("Getting labels failed", { error, errorMsg });
      if (error instanceof LokiClientError) {
        throw error;
      }
      throw new LokiClientError(
        "execution_failed",
        `Failed to get labels: ${errorMsg}`,
        {
          cause: error as Error,
          details: {
            command: "labels",
          },
        }
      );
    }
  }

• src/utils/loki-client.ts:329-416 (helper)

  Private getLabelsViaHttp(): Performs HTTP GET to /loki/api/v1/labels endpoint with auth headers, returns array of label names or throws LokiClientError.

  private async getLabelsViaHttp(): Promise<string[]> {
    try {
      const config = this.auth.getConfig();
  
      if (!config.addr) {
        throw new LokiClientError(
          "http_query_error",
          "Loki server address (addr) is not configured",
          { details: { command: "labels" } }
        );
      }
  
      // Build URL for labels endpoint
      const url = `${config.addr}/loki/api/v1/labels`;
  
      // Prepare request headers
      const headers: Record<string, string> = {};
  
      // Add authentication headers
      if (config.username && config.password) {
        const auth = Buffer.from(
          `${config.username}:${config.password}`
        ).toString("base64");
        headers["Authorization"] = `Basic ${auth}`;
      } else if (config.bearer_token) {
        headers["Authorization"] = `Bearer ${config.bearer_token}`;
      }
  
      if (config.tenant_id) {
        headers["X-Scope-OrgID"] = config.tenant_id;
      }
  
      if (config.org_id) {
        headers["X-Org-ID"] = config.org_id;
      }
  
      this.logger.debug("Executing HTTP labels query", {
        url,
        headers: {
          ...headers,
          Authorization: headers.Authorization ? "[REDACTED]" : undefined,
        },
      });
  
      // Make the HTTP request
      const response = await axios.get<{ status: string; data: string[] }>(
        url,
        {
          headers,
          // Handle TLS options
          ...(config.tls_skip_verify
            ? { httpsAgent: { rejectUnauthorized: false } }
            : {}),
        }
      );
  
      if (
        response.data &&
        response.data.data &&
        Array.isArray(response.data.data)
      ) {
        return response.data.data;
      }
  
      return [];
    } catch (error: unknown) {
      let errorMsg = "HTTP labels query failed";
      let errorDetails: Record<string, unknown> = { command: "labels" };
  
      if (axios.isAxiosError(error)) {
        const axiosError = error as AxiosError;
        errorMsg = `HTTP labels query failed: ${axiosError.message}`;
        errorDetails = {
          ...errorDetails,
          status: axiosError.response?.status,
          statusText: axiosError.response?.statusText,
          responseData: axiosError.response?.data,
        };
      } else if (error instanceof Error) {
        errorMsg = `HTTP labels query failed: ${error.message}`;
      }
  
      throw new LokiClientError("http_query_error", errorMsg, {
        cause: error as Error,
        details: errorDetails,
      });
    }
  }

• src/index.ts:180-200 (registration)

  Registration of the "get_labels" MCP tool with empty input schema and inline handler.

  server.tool("get_labels", {}, async (_args, extra) => {
    logger.debug("All labels query tool execution", { extra });
  
    try {
      const labelsJson = await lokiClient.getLabels();
  
      return {
        content: [
          {
            type: "text",
            text: labelsJson,
          },
        ],
      };
    } catch (error) {
      logger.error("Labels query tool execution error", { error });
  
      // Create standardized error response
      return createToolErrorResponse(error, "Error getting labels");
    }
  });