buildin-mcp

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Append children blocks

buildin_append_block_children

Append child blocks to a parent block or page using block types like paragraph, heading, list, and media. Returns the created blocks.

Instructions

Append one or more child blocks to a parent block (or page). children is an array of block objects ({type, data}). Returns the list of created blocks.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "block_id": "<block_id>",
      "children": "<children>"
    },
    "name": "buildin_append_block_children"
  }
}

Input Schema

Name	Required	Description
`block_id`	Yes	Buildin object ID (UUID-like).
`children`	Yes
`after`	No	Optional: ID of the child to insert the new children after.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.1Jun 18, 2026

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 bears full responsibility for behavioral disclosure. It states that the tool appends children and returns created blocks, but does not mention that this is a write operation, potential for data modification, permission requirements, rate limits, or error scenarios.

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 highly concise: two sentences that front-load the purpose and quickly explain the children format and return value. Every sentence earns its place without redundancy.

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 complexity of the input schema (many block types, nested rich text), the description is too sparse. It lacks information on allowed block types, nesting capabilities, error handling, and pagination of results. No output schema is provided, but the return value is mentioned, though not fully specified.

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 67%, so the description adds some value by summarizing the children parameter as an array of {type, data} objects. However, it does not elaborate on block_id or after beyond what the schema provides, and the schema already contains detailed structure for block objects.

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 child blocks to a parent block/page) and the resource (parent block/page). It indicates the input format (array of block objects with type and data) and the return value (list of created blocks). However, it does not distinguish from similar sibling tools like buildin_insert_blocks.

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 such as buildin_insert_blocks or buildin_append_markdown. The description does not specify prerequisites, limitations, or contexts where this tool is appropriate.

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