Validate the YAML front matter of a markdown file against a JSON Schema.
AI agents call validate_front_matter to retrieve information from Obsidian Markdown Lint without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs schema validation on existing markdown file metadata. It reads and checks YAML front matter for conformance to a schema but does not create, modify, delete, or execute anything. It has no side effects on the file system or external services. The blast radius of misuse is minimal — at worst, it could report false validation results, but cannot harm data or trigger external actions.
From the tool's definition Tool description states 'Validate the YAML front matter of a markdown file against a JSON Schema' — this is a validation/checking operation with no data modification.
Attacks that exploit this kind of access
Validate the YAML front matter of a markdown file against a JSON Schema. It is categorised as a Read tool in the Obsidian Markdown Lint MCP Server, which means it retrieves data without modifying state.
Register the Obsidian Markdown Lint MCP server in PolicyLayer and add a rule for validate_front_matter: 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 Obsidian Markdown Lint. Nothing to install.
validate_front_matter 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 validate_front_matter 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 validate_front_matter. 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.
validate_front_matter is provided by the Obsidian Markdown Lint MCP server (psenger/obsidian-markdown-lint-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
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