MCP Observatory

Instructions

Implementation Reference

• src/server.ts:101-125 (handler)

  The `diff_runs` tool is registered and implemented directly in `src/server.ts`. It takes `base` and `head` artifact paths as input, reads them, computes the diff using `diffArtifacts`, and returns a markdown representation.

  server.tool(
    "diff_runs",
    "Compare two run artifact files and return the diff showing regressions, recoveries, and schema drift.",
    {
      base: z.string().describe("Path to the base run artifact JSON file."),
      head: z.string().describe("Path to the head run artifact JSON file."),
    },
    async ({ base, head }) => {
      try {
        const baseArtifact = await readArtifact(base);
        const headArtifact = await readArtifact(head);
  
        if (baseArtifact.artifactType !== "run" || headArtifact.artifactType !== "run") {
          return { content: [{ type: "text" as const, text: "Both files must be run artifacts (not diff artifacts)." }], isError: true };
        }
  
        const diff = diffArtifacts(baseArtifact, headArtifact);
        const markdown = renderMarkdown(diff);
        return { content: [{ type: "text" as const, text: markdown }] };
      } catch (error) {
        const msg = error instanceof Error ? error.message : String(error);
        return { content: [{ type: "text" as const, text: `Error diffing runs: ${msg}` }], isError: true };
      }
    },
  );