AI agents use prepend_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.
The tool adds content (a child block) to a document, which is a write operation that modifies data but remains reversible—blocks can be moved, edited, or deleted later. It does not delete data (Destructive), execute arbitrary code (Execute), or move money (Financial).
From the tool's definition Tool name 'prepend_block' and description '插入前置子块' (insert preceding/prepend child block) indicate the tool creates or adds a new block before an existing one in SiYuan's document structure. This modifies document hierarchy reversibly.
Documented attack patterns abuse exactly the kind of access prepend_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 prepend_block:
{
"version": "1",
"default": "deny",
"tools": {
"prepend_block": {
"limits": [
{
"counter": "prepend_block_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}prepend_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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插入前置子块. 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 prepend_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.
prepend_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 prepend_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 prepend_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.
prepend_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.