Read a single .mmd file from a GitHub repository. Only paths ending in .mmd are allowed. REQUIRES: Github-Token header (HTTP) or GITHUB_TOKEN / GH_TOKEN.
Risk signalsAccepts file system path (path)
Part of the Mermaid Mcp server.
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AI agents call read_mermaid_file to retrieve information from Mermaid Mcp without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though read_mermaid_file only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"read_mermaid_file": {}
}
}See the full Mermaid Mcp policy for all 17 tools.
These attack patterns abuse exactly the kind of access read_mermaid_file gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
Read a single .mmd file from a GitHub repository. Only paths ending in .mmd are allowed. REQUIRES: Github-Token header (HTTP) or GITHUB_TOKEN / GH_TOKEN.. It is categorised as a Read tool in the Mermaid Mcp MCP Server, which means it retrieves data without modifying state.
Register the Mermaid MCP server in PolicyLayer and add a rule for read_mermaid_file: 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 Mermaid Mcp. Nothing to install.
read_mermaid_file is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the read_mermaid_file 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 read_mermaid_file. 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.
read_mermaid_file is provided by the Mermaid MCP server (https://mcp.mermaidchart.com/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 17 Mermaid Mcp tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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