Instructions

Implementation Reference

• src/tools.ts:294-304 (handler)

  MCP tool handler for 'lookup_context'. Awaits parser instance, invokes parser.lookupContext with parameters, and returns JSON-formatted result as text content.

  handler: async ({ line, column, sourceMapUrl, contextLines }, getParser) => {
    const parser = await getParser();
    const result = await parser.lookupContext(line, column, sourceMapUrl, contextLines);
  
    return {
      content: [{
        type: "text",
        text: JSON.stringify(result, null, 2)
      }],
    }
  }

• src/tools.ts:280-293 (schema)

  Zod input schema for 'lookup_context' tool parameters: line (number), column (number), sourceMapUrl (string), contextLines (optional number, default 5).

  schema: {
    line: z.number({
      description: "The line number in the compiled code (1-based)",
    }),
    column: z.number({
      description: "The column number in the compiled code",
    }),
    sourceMapUrl: z.string({
      description: "The URL of the source map file",
    }),
    contextLines: z.number({
      description: "Number of context lines to include (default: 5)",
    }).optional().default(5),
  },

• src/tools.ts:263-305 (registration)

  Declarative tool definition object for 'lookup_context' in toolDefinitions array, used by registerTools to conditionally register the tool with the MCP server via server.tool().

      {
        name: "lookup_context",
        description: `
    # 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
  `,
        schema: {
          line: z.number({
            description: "The line number in the compiled code (1-based)",
          }),
          column: z.number({
            description: "The column number in the compiled code",
          }),
          sourceMapUrl: z.string({
            description: "The URL of the source map file",
          }),
          contextLines: z.number({
            description: "Number of context lines to include (default: 5)",
          }).optional().default(5),
        },
        handler: async ({ line, column, sourceMapUrl, contextLines }, getParser) => {
          const parser = await getParser();
          const result = await parser.lookupContext(line, column, sourceMapUrl, contextLines);
  
          return {
            content: [{
              type: "text",
              text: JSON.stringify(result, null, 2)
            }],
          }
        }
      },

• src/parser.ts:393-408 (helper)

  Core helper method in Parser class: lookupContext. Validates URL, fetches source map content, initializes parser, calls external sourceMapParser.lookup_context WASM function, and returns the source context result. Invoked by the tool handler.

  public async lookupContext(line: number, column: number, sourceMapUrl: string, contextLines: number = 5) {
    validateUrl(sourceMapUrl);
    await this.init();
  
    try {
      const sourceMapContent = await this.fetchSourceMapContent(sourceMapUrl);
      // Use the high-level lookup_context function directly
      const result = sourceMapParser.lookup_context(sourceMapContent, line, column, contextLines);
  
      return result;
    } catch (error) {
      throw new Error("lookup context error: " + (error instanceof Error ? error.message : error), {
        cause: error,
      });
    }
  }