AI agents use update_prompt to create or update resources in MCP Prompts Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MCP Prompts Server environment.
This tool creates or modifies data reversibly without deleting or destroying it (Write category). Severity is medium because misuse could result in prompt injection, altered system behaviors, or corrupted prompt templates, but effects are reversible through re-updates.
From the tool's definition Tool description states 'Update an existing prompt', which modifies existing data. The server description confirms it enables 'management...of prompts', indicating reversible modifications to stored prompt objects.
Documented attack patterns abuse exactly the kind of access update_prompt gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Prompts Server, and nothing reaches the server without passing your rules. This is the rule we recommend for update_prompt:
{
"version": "1",
"default": "deny",
"tools": {
"update_prompt": {
"limits": [
{
"counter": "update_prompt_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_prompt 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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Update an existing prompt. It is categorised as a Write tool in the MCP Prompts Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the MCP Prompts Server MCP server in PolicyLayer and add a rule for update_prompt: 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 MCP Prompts Server. Nothing to install.
update_prompt 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 update_prompt 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 update_prompt. 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.
update_prompt is provided by the MCP Prompts Server MCP server (sparesparrow/mcp-prompts). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 51 MCP Prompts Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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51 MCP Prompts Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.