AI agents use append_block to create or update resources in SiYuan MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your SiYuan MCP Server environment.
This tool creates or modifies document content by appending new blocks, which is reversible (blocks can be deleted or edited). It does not execute arbitrary code, delete data irreversibly, or move money. It falls under Write category as it creates/modifies data within the note system.
From the tool's definition Tool name 'append_block' and description '插入后置子块' (insert child block after) indicate creation/modification of document structure by appending blocks to existing blocks in SiYuan notes.
Documented attack patterns abuse exactly the kind of access append_block gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and SiYuan MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for append_block:
{
"version": "1",
"default": "deny",
"tools": {
"append_block": {
"limits": [
{
"counter": "append_block_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}append_block stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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插入后置子块. It is categorised as a Write tool in the SiYuan MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the SiYuan MCP Server MCP server in PolicyLayer and add a rule for append_block: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches SiYuan MCP Server. Nothing to install.
append_block is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the append_block rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for append_block. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
append_block is provided by the SiYuan MCP Server MCP server (xgq18237/siyuan_mcp_server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 52 SiYuan MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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52 SiYuan MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.