Notion MCP Server

Instructions

Implementation Reference

• src/openapi-mcp-server/mcp/proxy.ts:78-119 (handler)

  Generic MCP tool call handler that implements the logic for 'API-retrieve-a-comment' by looking up the corresponding OpenAPI operation in openApiLookup and proxying the HTTP request via httpClient.executeOperation.

  this.server.setRequestHandler(CallToolRequestSchema, async (request) => {
    const { name, arguments: params } = request.params
  
    // Find the operation in OpenAPI spec
    const operation = this.findOperation(name)
    if (!operation) {
      throw new Error(`Method ${name} not found`)
    }
  
    try {
      // Execute the operation
      const response = await this.httpClient.executeOperation(operation, params)
  
      // Convert response to MCP format
      return {
        content: [
          {
            type: 'text', // currently this is the only type that seems to be used by mcp server
            text: JSON.stringify(response.data), // TODO: pass through the http status code text?
          },
        ],
      }
    } catch (error) {
      console.error('Error in tool call', error)
      if (error instanceof HttpClientError) {
        console.error('HttpClientError encountered, returning structured error', error)
        const data = error.data?.response?.data ?? error.data ?? {}
        return {
          content: [
            {
              type: 'text',
              text: JSON.stringify({
                status: 'error', // TODO: get this from http status code?
                ...(typeof data === 'object' ? data : { data: data }),
              }),
            },
          ],
        }
      }
      throw error
    }
  })

• src/openapi-mcp-server/mcp/proxy.ts:57-75 (registration)

  MCP listTools request handler that dynamically registers and lists all tools, constructing the name 'API-retrieve-a-comment' from the OpenAPI operationId 'retrieve-a-comment'.

  // Handle tool listing
  this.server.setRequestHandler(ListToolsRequestSchema, async () => {
    const tools: Tool[] = []
  
    // Add methods as separate tools to match the MCP format
    Object.entries(this.tools).forEach(([toolName, def]) => {
      def.methods.forEach(method => {
        const toolNameWithMethod = `${toolName}-${method.name}`;
        const truncatedToolName = this.truncateToolName(toolNameWithMethod);
        tools.push({
          name: truncatedToolName,
          description: method.description,
          inputSchema: method.inputSchema as Tool['inputSchema'],
        })
      })
    })
  
    return { tools }
  })

• src/openapi-mcp-server/openapi/parser.ts:362-475 (schema)

  Generates the inputSchema and optional returnSchema for MCP tools from OpenAPI operations, used for 'retrieve-a-comment'.

  private convertOperationToMCPMethod(operation: OpenAPIV3.OperationObject, method: string, path: string): NewToolMethod | null {
    if (!operation.operationId) {
      console.warn(`Operation without operationId at ${method} ${path}`)
      return null
    }
  
    const methodName = operation.operationId
  
    const inputSchema: IJsonSchema & { type: 'object' } = {
      $defs: this.convertComponentsToJsonSchema(),
      type: 'object',
      properties: {},
      required: [],
    }
  
    // Handle parameters (path, query, header, cookie)
    if (operation.parameters) {
      for (const param of operation.parameters) {
        const paramObj = this.resolveParameter(param)
        if (paramObj && paramObj.schema) {
          const schema = this.convertOpenApiSchemaToJsonSchema(paramObj.schema, new Set(), false)
          // Merge parameter-level description if available
          if (paramObj.description) {
            schema.description = paramObj.description
          }
          inputSchema.properties![paramObj.name] = schema
          if (paramObj.required) {
            inputSchema.required!.push(paramObj.name)
          }
        }
      }
    }
  
    // Handle requestBody
    if (operation.requestBody) {
      const bodyObj = this.resolveRequestBody(operation.requestBody)
      if (bodyObj?.content) {
        // Handle multipart/form-data for file uploads
        // We convert the multipart/form-data schema to a JSON schema and we require
        // that the user passes in a string for each file that points to the local file
        if (bodyObj.content['multipart/form-data']?.schema) {
          const formSchema = this.convertOpenApiSchemaToJsonSchema(bodyObj.content['multipart/form-data'].schema, new Set(), false)
          if (formSchema.type === 'object' && formSchema.properties) {
            for (const [name, propSchema] of Object.entries(formSchema.properties)) {
              inputSchema.properties![name] = propSchema
            }
            if (formSchema.required) {
              inputSchema.required!.push(...formSchema.required!)
            }
          }
        }
        // Handle application/json
        else if (bodyObj.content['application/json']?.schema) {
          const bodySchema = this.convertOpenApiSchemaToJsonSchema(bodyObj.content['application/json'].schema, new Set(), false)
          // Merge body schema into the inputSchema's properties
          if (bodySchema.type === 'object' && bodySchema.properties) {
            for (const [name, propSchema] of Object.entries(bodySchema.properties)) {
              inputSchema.properties![name] = propSchema
            }
            if (bodySchema.required) {
              inputSchema.required!.push(...bodySchema.required!)
            }
          } else {
            // If the request body is not an object, just put it under "body"
            inputSchema.properties!['body'] = bodySchema
            inputSchema.required!.push('body')
          }
        }
      }
    }
  
    // Build description including error responses
    let description = operation.summary || operation.description || ''
    if (operation.responses) {
      const errorResponses = Object.entries(operation.responses)
        .filter(([code]) => code.startsWith('4') || code.startsWith('5'))
        .map(([code, response]) => {
          const responseObj = this.resolveResponse(response)
          let errorDesc = responseObj?.description || ''
          return `${code}: ${errorDesc}`
        })
  
      if (errorResponses.length > 0) {
        description += '\nError Responses:\n' + errorResponses.join('\n')
      }
    }
  
    // Extract return type (response schema)
    const returnSchema = this.extractResponseType(operation.responses)
  
    // Generate Zod schema from input schema
    try {
      // const zodSchemaStr = jsonSchemaToZod(inputSchema, { module: "cjs" })
      // console.log(zodSchemaStr)
      // // Execute the function with the zod instance
      // const zodSchema = eval(zodSchemaStr) as z.ZodType
  
      return {
        name: methodName,
        description,
        inputSchema,
        ...(returnSchema ? { returnSchema } : {}),
      }
    } catch (error) {
      console.warn(`Failed to generate Zod schema for ${methodName}:`, error)
      // Fallback to a basic object schema
      return {
        name: methodName,
        description,
        inputSchema,
        ...(returnSchema ? { returnSchema } : {}),
      }
    }
  }

• src/openapi-mcp-server/mcp/proxy.ts:47-54 (helper)

  Initializes the tools map and openApiLookup dictionary in MCPProxy constructor, populating entries like openApiLookup['API-retrieve-a-comment'] from the OpenAPI spec.

    // Convert OpenAPI spec to MCP tools
    const converter = new OpenAPIToMCPConverter(openApiSpec)
    const { tools, openApiLookup } = converter.convertToMCPTools()
    this.tools = tools
    this.openApiLookup = openApiLookup
  
    this.setupHandlers()
  }