Langfuse MCP Server

Instructions

Input Schema

Input Schema (JSON Schema)

Implementation Reference

• src/tools/get-metrics.ts:29-117 (handler)

  The core handler function that executes the get_metrics tool: validates args, calls Langfuse client.getMetrics, processes and aggregates the response data, and returns formatted JSON.
  export async function getMetrics( client: LangfuseAnalyticsClient, args: z.infer<typeof getMetricsSchema> ) { const filters: any[] = args.filters || []; // Add environment filter if specified if (args.environment) { filters.push({ column: 'environment', operator: 'equals', value: args.environment, type: 'string', }); } const response = await client.getMetrics({ view: args.view, from: args.from, to: args.to, metrics: args.metrics, dimensions: args.dimensions, filters, }); // Process the response into a structured format const metricsResult: MetricsResponse = { projectId: client.getProjectId(), from: args.from, to: args.to, view: args.view, metrics: [], dimensions: [], }; // Parse metrics data from response if (response.data && Array.isArray(response.data)) { // Aggregate metrics across all rows const aggregatedMetrics: Record<string, number> = {}; response.data.forEach((row: any) => { args.metrics.forEach(metric => { const key = `${metric.measure}_${metric.aggregation}`; // Metrics API returns aggregated field names like 'totalCost_sum', 'count_count' const aggregatedFieldName = `${metric.measure}_${metric.aggregation}`; if (row[aggregatedFieldName] !== undefined) { if (metric.aggregation === 'sum' || metric.aggregation === 'count') { aggregatedMetrics[key] = (aggregatedMetrics[key] || 0) + (row[aggregatedFieldName] || 0); } else if (metric.aggregation === 'avg') { // For average, we'll need to handle this differently aggregatedMetrics[key] = row[aggregatedFieldName] || 0; } } }); }); // Convert aggregated metrics to result format metricsResult.metrics = Object.entries(aggregatedMetrics).map(([key, value]) => { const [measure, aggregation] = key.split('_'); return { measure, aggregation, value }; }); // Extract dimension data if present if (args.dimensions && response.data.length > 0) { const dimensions = new Set<string>(); response.data.forEach((row: any) => { args.dimensions?.forEach(dim => { if (row[dim.field] !== undefined) { dimensions.add(`${dim.field}:${row[dim.field]}`); } }); }); metricsResult.dimensions = Array.from(dimensions).map(dimStr => { const [field, value] = dimStr.split(':'); return { field, value }; }); } } return { content: [ { type: 'text' as const, text: JSON.stringify(metricsResult, null, 2), }, ], }; }
• src/tools/get-metrics.ts:5-27 (schema)

  Zod schema defining the input parameters for the get_metrics tool, used for validation in the handler and dispatcher.
  export const getMetricsSchema = z.object({ from: z.string().datetime(), to: z.string().datetime(), view: z.enum(['traces', 'observations']).default('traces'), metrics: z.array(z.object({ measure: z.string(), aggregation: z.string(), })).default([ { measure: 'totalCost', aggregation: 'sum' }, { measure: 'totalTokens', aggregation: 'sum' }, { measure: 'count', aggregation: 'count' }, ]), dimensions: z.array(z.object({ field: z.string(), })).optional(), filters: z.array(z.object({ column: z.string(), operator: z.string(), value: z.any(), type: z.string().optional(), })).optional(), environment: z.string().optional(), });
• src/index.ts:1036-1039 (registration)

  Tool registration in the main switch dispatcher: parses arguments with schema and invokes the getMetrics handler.
  case 'get_metrics': { const args = getMetricsSchema.parse(request.params.arguments); return await getMetrics(this.client, args); }
• src/index.ts:298-346 (registration)

  Tool metadata registration including name, description, and JSON inputSchema in the listTools response.
  { name: 'get_metrics', description: 'Query aggregated metrics (costs, tokens, counts) with flexible filtering and dimensions.', inputSchema: { type: 'object', properties: { from: { type: 'string', format: 'date-time', description: 'Start timestamp (ISO 8601)', }, to: { type: 'string', format: 'date-time', description: 'End timestamp (ISO 8601)', }, view: { type: 'string', enum: ['traces', 'observations'], description: 'Data view to query (default: traces)', }, metrics: { type: 'array', items: { type: 'object', properties: { measure: { type: 'string' }, aggregation: { type: 'string' }, }, }, description: 'Metrics to aggregate', }, dimensions: { type: 'array', items: { type: 'object', properties: { field: { type: 'string' }, }, }, description: 'Dimensions to group by', }, environment: { type: 'string', description: 'Optional environment filter', }, }, required: ['from', 'to'], },
• src/index.ts:59-59 (registration)

  Import statement bringing in the getMetrics handler and schema from the tool module.
  import { getMetrics, getMetricsSchema } from './tools/get-metrics.js';