This record as markdown: /tools/io-github-dave-london-npm/yq.md
What yq does on Npm
AI agents invoke yq to trigger actions in Npm. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
Why yq is rated High
The tool executes arbitrary yq expressions against files or inline data. yq expressions can read, modify, and write back structured data files. Since it accepts arbitrary expressions and can write transformed results (potentially back to files), this goes beyond a simple read operation.
From the tool's definition Processes and transforms YAML, JSON, XML, TOML, and properties files using yq expressions
Attacks that exploit this kind of access
The rule that runs yq safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Npm, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For yq, this is the rule to start with:
yq stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Npm, apply this rule, and every yq call is checked against it from then on.
Questions about yq
Processes and transforms YAML, JSON, XML, TOML, and properties files using yq expressions. Accepts input from a file path or inline string. Returns the transformed result. It is categorised as a Execute tool in the Npm MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Npm MCP server in PolicyLayer and add a rule for yq: 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 Npm. Nothing to install.
yq is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the yq 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 yq. 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.
yq is provided by the Npm MCP server (Dave-London/Pare). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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