# Lookup Source Code Context This tool looks up original source code context for a specific line and column position in compiled/minified code. ## Parameters: - line: The line number in the compiled code (1-based) - column: The column number in the compiled code - sourceMapUrl: The URL of the sou...
Part of the Source Map Parser server.
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AI agents call lookup_context to retrieve information from Source Map Parser 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 lookup_context 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": {
"lookup_context": {}
}
}See the full Source Map Parser policy for all 3 tools.
These attack patterns abuse exactly the kind of access lookup_context 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.
# Lookup Source Code Context This tool looks up original source code context for a specific line and column position in compiled/minified code. ## Parameters: - line: The line number in the compiled code (1-based) - column: The column number in the compiled code - sourceMapUrl: The URL of the source map file - contextLines (optional): Number of context lines to include before and after the target line (default: 5) ## Returns: - A JSON object containing the source code context snippet with file path, target line info, and surrounding context lines - Returns null if the position cannot be mapped. It is categorised as a Read tool in the Source Map Parser MCP Server, which means it retrieves data without modifying state.
Register the Source Map Parser MCP server in PolicyLayer and add a rule for lookup_context: 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 Source Map Parser. Nothing to install.
lookup_context 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 lookup_context 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 lookup_context. 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.
lookup_context is provided by the Source Map Parser MCP server (source-map-parser-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 3 Source Map Parser tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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