API-get-block-children
Retrieve child blocks from a Notion page using a block ID. Supports pagination with start cursor and page size to manage large datasets efficiently.
Instructions
Notion | Retrieve block children
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| block_id | Yes | Identifier for a [block](ref:block) | |
| page_size | No | The number of items from the full list desired in the response. Maximum: 100 | |
| start_cursor | No | If supplied, this endpoint will return a page of results starting after the cursor provided. If not supplied, this endpoint will return the first page of results. |
Implementation Reference
- Handler for callTool requests. For 'API-get-block-children', it looks up the corresponding OpenAPI operation by name, executes it via HTTPClient, and returns the JSON response as text content.
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 ${name} not found`) } try { // Execute the operation const response = await this.httpClient.executeOperation(operation, params) // Convert response to MCP format return { content: [ { type: 'text', // currently this is the only type that seems to be used by mcp server text: JSON.stringify(response.data), // TODO: pass through the http status code text? }, ], } } catch (error) { console.error('Error in tool call', error) if (error instanceof HttpClientError) { console.error('HttpClientError encountered, returning structured error', error) const data = error.data?.response?.data ?? error.data ?? {} return { content: [ { type: 'text', text: JSON.stringify({ status: 'error', // TODO: get this from http status code? ...(typeof data === 'object' ? data : { data: data }), }), }, ], } } throw error } }) - src/openapi-mcp-server/mcp/proxy.ts:58-75 (registration)Registration of listTools handler which dynamically lists all tools. 'API-get-block-children' is constructed as 'API-' + operationId (get-block-children) from the OpenAPI spec, truncated if necessary.
this.server.setRequestHandler(ListToolsRequestSchema, async () => { const tools: Tool[] = [] // Add methods as separate tools to match the MCP format Object.entries(this.tools).forEach(([toolName, def]) => { def.methods.forEach(method => { const toolNameWithMethod = `${toolName}-${method.name}`; const truncatedToolName = this.truncateToolName(toolNameWithMethod); tools.push({ name: truncatedToolName, description: method.description, inputSchema: method.inputSchema as Tool['inputSchema'], }) }) }) return { tools } }) - Generates the inputSchema and description for each MCP tool method based on the OpenAPI operation's parameters and requestBody. Used for 'get-block-children' operation.
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 } : {}), } } } - Converts OpenAPI spec to MCP tools structure. Defines tool names as 'API-{operationId}' (e.g., 'API-get-block-children'), builds tools record and openApiLookup used for dispatching.
convertToMCPTools(): { tools: Record<string, { methods: NewToolMethod[] }> openApiLookup: Record<string, OpenAPIV3.OperationObject & { method: string; path: string }> zip: Record<string, { openApi: OpenAPIV3.OperationObject & { method: string; path: string }; mcp: NewToolMethod }> } { const apiName = 'API' const openApiLookup: Record<string, OpenAPIV3.OperationObject & { method: string; path: string }> = {} const tools: Record<string, { methods: NewToolMethod[] }> = { [apiName]: { methods: [] }, } const zip: Record<string, { openApi: OpenAPIV3.OperationObject & { method: string; path: string }; mcp: NewToolMethod }> = {} for (const [path, pathItem] of Object.entries(this.openApiSpec.paths || {})) { if (!pathItem) continue for (const [method, operation] of Object.entries(pathItem)) { if (!this.isOperation(method, operation)) continue const mcpMethod = this.convertOperationToMCPMethod(operation, method, path) if (mcpMethod) { const uniqueName = this.ensureUniqueName(mcpMethod.name) mcpMethod.name = uniqueName mcpMethod.description = this.getDescription(operation.summary || operation.description || '') tools[apiName]!.methods.push(mcpMethod) openApiLookup[apiName + '-' + uniqueName] = { ...operation, method, path } zip[apiName + '-' + uniqueName] = { openApi: { ...operation, method, path }, mcp: mcpMethod } } } } return { tools, openApiLookup, zip } } - MCPProxy constructor initializes the server, HTTP client with Notion headers, converts OpenAPI to MCP tools/schemas, and sets up handlers. Called with 'Notion API' name.
constructor(name: string, openApiSpec: OpenAPIV3.Document) { this.server = new Server({ name, version: '1.0.0' }, { capabilities: { tools: {} } }) const baseUrl = openApiSpec.servers?.[0].url if (!baseUrl) { throw new Error('No base URL found in OpenAPI spec') } this.httpClient = new HttpClient( { baseUrl, headers: this.parseHeadersFromEnv(), }, openApiSpec, ) // Convert OpenAPI spec to MCP tools const converter = new OpenAPIToMCPConverter(openApiSpec) const { tools, openApiLookup } = converter.convertToMCPTools() this.tools = tools this.openApiLookup = openApiLookup this.setupHandlers() }