AI agents use add_double_bar to create or update resources in Guitar Pro — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Guitar Pro environment.
This tool creates or modifies a musical notation element (a double bar) within a Guitar Pro file. It is reversible (the modification can be undone or overwritten), making it a Write operation. Severity is medium because misuse could corrupt a musical score, but the effect is limited to a single file and reversible.
From the tool's definition Tool name 'add_double_bar' combined with sibling tools that all modify Guitar Pro files (add_chord, add_gp_measure, add_gp_note, add_gp_track, etc.).
Documented attack patterns abuse exactly the kind of access add_double_bar gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Guitar Pro, and nothing reaches the server without passing your rules. This is the rule we recommend for add_double_bar:
{
"version": "1",
"default": "deny",
"tools": {
"add_double_bar": {
"limits": [
{
"counter": "add_double_bar_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_double_bar 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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add_double_bar. It is categorised as a Write tool in the Guitar Pro MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Guitar Pro MCP server in PolicyLayer and add a rule for add_double_bar: 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 Guitar Pro. Nothing to install.
add_double_bar 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 add_double_bar 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 add_double_bar. 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.
add_double_bar is provided by the Guitar Pro MCP server (wegitor/guitar-pro-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Guitar Pro, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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35 Guitar Pro tools catalogued and risk-classified — across an index of 43,000+ MCP servers.