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Notion MCP Server

by gendosu

API-patch-block-children

Append child content to a Notion block or page using the Notion MCP Server. Specify block ID and array of child blocks to add content after an existing block, enhancing workspace organization.

Instructions

Notion | Append block children

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
afterNoThe ID of the existing block that the new block should be appended after.
block_idYesIdentifier for a [block](ref:block). Also accepts a [page](ref:page) ID.
childrenYesChild content to append to a container block as an array of [block objects](ref:block)

Implementation Reference

  • Generic MCP tool execution handler for all tools derived from OpenAPI spec, including "API-patch-block-children". It resolves the tool name to the corresponding OpenAPI operation (PATCH /v1/blocks/{block_id}/children), executes the HTTP request via HttpClient, and formats the response as MCP 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
      }
    })
  • MCP tool listing handler that registers all OpenAPI-derived tools, constructing names like "API-patch-block-children" from 'API' + operationId 'patch-block-children', including description and inputSchema.
    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 MCP tool definitions (name, description, inputSchema) from OpenAPI operations, creating the "API-patch-block-children" tool from Notion's patchBlockChildren operation including schema for path param block_id and body.
    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 }
    }
  • Initializes the MCPProxy by converting Notion OpenAPI spec to internal tools map and openApiLookup (used for dispatching), including the entry for "API-patch-block-children".
      const converter = new OpenAPIToMCPConverter(openApiSpec)
      const { tools, openApiLookup } = converter.convertToMCPTools()
      this.tools = tools
      this.openApiLookup = openApiLookup
    
      this.setupHandlers()
    }
  • Dispatches to HttpClient.executeOperation which performs the actual HTTP PATCH request for the tool.
    const response = await this.httpClient.executeOperation(operation, params)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

C2.9/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries full burden but only states the action without behavioral details. It doesn't disclose if this is a mutation (implied by 'Append'), permission requirements, rate limits, error conditions, or what happens on success/failure, which is inadequate for a tool that modifies data.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely concise with just three words, front-loading key information ('Notion | Append block children') without waste. Every word contributes to understanding the tool's domain and action efficiently.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (mutation with 3 parameters, no output schema, and no annotations), the description is incomplete. It lacks details on behavior, return values, error handling, and how it differs from siblings, making it insufficient for safe and effective use by an AI agent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so parameters are well-documented in the schema. The description adds no additional meaning beyond implying 'append' relates to 'block children', but doesn't explain parameter interactions or constraints, meeting the baseline for high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Append') and resource ('block children') with platform context ('Notion'), making the purpose understandable. However, it doesn't distinguish this from sibling tools like 'API-update-a-block' or 'API-get-block-children' beyond the 'append' verb, missing explicit differentiation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is provided on when to use this tool versus alternatives. The description lacks context about prerequisites (e.g., needing an existing block), exclusions, or comparisons to siblings like 'API-update-a-block' or 'API-get-block-children', leaving usage ambiguous.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.