Set the key signature in the live score.
AI agents use set_live_key_signature to create or update resources in Mcp Score — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mcp Score environment.
This tool creates or modifies score data reversibly. Setting a key signature is a standard Write operation—it changes the live score state but does not delete data, execute arbitrary code, or produce irreversible side effects. The user can undo or change the key signature again. The blast radius is limited to the current score's key signature property, making severity low.
From the tool's definition The tool name 'set_live_key_signature' and description 'Set the key signature in the live score' indicate a modification operation that changes musical notation metadata (key signature) in an active score document.
Documented attack patterns abuse exactly the kind of access set_live_key_signature gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Score, and nothing reaches the server without passing your rules. This is the rule we recommend for set_live_key_signature:
{
"version": "1",
"default": "deny",
"tools": {
"set_live_key_signature": {
"limits": [
{
"counter": "set_live_key_signature_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_live_key_signature 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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Set the key signature in the live score. It is categorised as a Write tool in the Mcp Score MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Score MCP server in PolicyLayer and add a rule for set_live_key_signature: 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 Score. Nothing to install.
set_live_key_signature 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 set_live_key_signature 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 set_live_key_signature. 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.
set_live_key_signature is provided by the Mcp Score MCP server (tskovlund/mcp-score). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Mcp Score, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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18 Mcp Score tools catalogued and risk-classified — across an index of 43,000+ MCP servers.