Prism MCP

Instructions

Implementation Reference

• src/tools/handlers.ts:148-184 (handler)

  The handler function `codeModeTransformHandler` that executes the code string against the provided data in a sandbox.

  export async function codeModeTransformHandler(args: unknown) {
    if (!isCodeModeTransformArgs(args)) {
      throw new Error("Invalid arguments for code_mode_transform");
    }
  
    const { data, code, language = "javascript", source_tool = "unknown" } = args;
  
    if (language.toLowerCase() !== "javascript") {
      return {
        content: [{ type: "text", text: "Unsupported language. Only 'javascript' is supported." }],
        isError: true,
      };
    }
  
    const beforeSizeKB = (Buffer.byteLength(data, "utf8") / 1024).toFixed(1);
    console.error(`[code_mode_transform] source=${source_tool}, input=${beforeSizeKB}KB`);
  
    const { stdout, error, executionTimeMs } = await runInSandbox(data, code);
  
    if (error) {
      return {
        content: [{ type: "text", text: `Sandboxed Execution Failed:\n${error}` }],
        isError: true,
      };
    }
  
    const finalOutput = stdout.trim() || "[No output from script]";
    const afterSizeKB = (Buffer.byteLength(finalOutput, "utf8") / 1024).toFixed(1);
    const reductionPct = (100 - (Number(afterSizeKB) / Number(beforeSizeKB)) * 100).toFixed(1);
  
    const header = `[code-mode-transform (${source_tool}): ${beforeSizeKB}KB -> ${afterSizeKB}KB (${reductionPct}% reduction) in ${executionTimeMs}ms]\n\n`;
  
    return {
      content: [{ type: "text", text: header + finalOutput }],
      isError: false,
    };
  }

• src/tools/definitions.ts:181-214 (schema)

  The definition of the `CODE_MODE_TRANSFORM_TOOL` including its input schema and description.

  export const CODE_MODE_TRANSFORM_TOOL: Tool = {
    name: "code_mode_transform",
    description:
      "A universal code-mode transformer. Takes RAW TEXT or JSON output from ANY MCP tool (GitHub, Firecrawl, chrome-devtools, camoufox, codegraphcontext, videoMcp, arxiv, etc.) " +
      "and runs a custom JavaScript code string against it in a secure QuickJS sandbox. " +
      "Use this as a second step after calling any tool that returns large payloads — pass the raw output as 'data' and a JS extraction script as 'code'. " +
      "Your script reads the 'DATA' global variable (a string of the tool output) and uses console.log() to print only the fields you need. " +
      "Typical use cases: extract only issue titles/IDs from GitHub list_issues, pull specific selectors from DOM snapshots, summarize crawl results, extract timestamps from video transcripts.",
    inputSchema: {
      type: "object",
      properties: {
        data: {
          type: "string",
          description: "The raw text or JSON output from another MCP tool to process.",
        },
        code: {
          type: "string",
          description:
            "JavaScript code to execute. The 'DATA' global variable contains the raw data string. Use console.log() to output your extraction. " +
            "Example: `var d = JSON.parse(DATA); console.log(d.items.map(function(i){return i.title}).join('\\n'));`",
        },
        language: {
          type: "string",
          description: "Language of the code. Only 'javascript' is supported.",
          default: "javascript",
        },
        source_tool: {
          type: "string",
          description: "Optional. Name of the MCP tool that produced the data (for logging/metrics only).",
        },
      },
      required: ["data", "code"],
    },
  };

• src/tools/definitions.ts:356-367 (helper)

  The `isCodeModeTransformArgs` type guard function used to validate the arguments for the tool.

  export function isCodeModeTransformArgs(
    args: unknown
  ): args is { data: string; code: string; language?: string; source_tool?: string } {
    return (
      typeof args === "object" &&
      args !== null &&
      "data" in args &&
      typeof (args as { data: string }).data === "string" &&
      "code" in args &&
      typeof (args as { code: string }).code === "string"
    );
  }