devutils-mcp-server

Instructions

Implementation Reference

• src/tools/text.ts:205-271 (handler)

  Implementation of the regex_test tool, which tests a regular expression against a string.

  server.tool(
    "regex_test",
    "Test a regular expression pattern against an input string. Returns all matches with groups and indices.",
    {
      pattern: z.string().describe("The regex pattern (without delimiters)"),
      flags: z
        .string()
        .default("g")
        .describe("Regex flags (default: 'g')"),
      input: z.string().describe("The string to test against"),
    },
    async ({ pattern, flags, input }) => {
      try {
        const regex = new RegExp(pattern, flags);
        const matches: Array<{
          match: string;
          index: number;
          groups: Record<string, string> | null;
        }> = [];
  
        let m;
        if (flags.includes("g")) {
          while ((m = regex.exec(input)) !== null) {
            matches.push({
              match: m[0],
              index: m.index,
              groups: m.groups ? { ...m.groups } : null,
            });
            if (matches.length > 100) break; // Safety limit
          }
        } else {
          m = regex.exec(input);
          if (m) {
            matches.push({
              match: m[0],
              index: m.index,
              groups: m.groups ? { ...m.groups } : null,
            });
          }
        }
  
        const result = {
          pattern,
          flags,
          input_length: input.length,
          matches_found: matches.length,
          matches,
        };
  
        return {
          content: [
            { type: "text" as const, text: JSON.stringify(result, null, 2) },
          ],
        };
      } catch (e) {
        return {
          content: [
            {
              type: "text" as const,
              text: `Error: Invalid regex — ${e instanceof Error ? e.message : String(e)}`,
            },
          ],
          isError: true,
        };
      }
    }
  );