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.
This record as markdown: /tools/io-github-dave-london-build/yq.md
What yq does on Build
AI agents invoke yq to trigger actions in Build. 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
yq supports arbitrary expressions including write operations, file mutations, and shell-like pipelines. Even if the primary purpose is data transformation/querying, yq expressions can modify and overwrite files in place (e.g., `yq -i` for in-place edits), making this an Execute-level tool.
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 Build, 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 Build, 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 Build MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Build 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 Build. 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 Build 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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