import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
ListPromptsRequestSchema,
GetPromptRequestSchema,
ListToolsRequestSchema,
CallToolRequestSchema,
} from "@modelcontextprotocol/sdk/types.js";
import { z } from "zod";
import { execFile } from "node:child_process";
import { promisify } from "node:util";
const execFileAsync = promisify(execFile);
// IMPORTANT: stdio MCP servers must not write logs to stdout.
// stdout is reserved for protocol messages.
function log(...args: unknown[]) {
process.stderr.write(args.map(String).join(" ") + "\n");
}
const server = new Server(
{ name: "mcp-house-rules", version: "0.1.0" },
{
capabilities: {
tools: {},
prompts: {},
},
}
);
// 1) List prompts: lets clients discover what templates exist.
server.setRequestHandler(ListPromptsRequestSchema, async () => {
return {
prompts: [
{
name: "house_rules",
description:
"Reusable instructions for how I want the assistant to behave (safe, scoped, and consistent).",
arguments: [
{
name: "mode",
description:
"Optional: what kind of work we are doing (review, triage, release-notes).",
required: false,
},
],
},
],
};
});
// 2) Get prompt: returns the actual prompt content.
server.setRequestHandler(GetPromptRequestSchema, async (request) => {
if (request.params.name !== "house_rules") {
throw new Error(`Unknown prompt: ${request.params.name}`);
}
const mode =
typeof request.params.arguments?.mode === "string"
? request.params.arguments.mode
: "general";
const text = [
"You are my coding assistant.",
"",
"Operating rules:",
"1) Prefer safe and reversible actions. Start read-only.",
"2) Summarize what you plan to do before you do it.",
"3) Keep scope small. If a task is large, propose the smallest next step.",
"4) Be explicit. Use checklists and concrete commands.",
"5) If you are blocked, ask one clarifying question. Otherwise proceed.",
"",
`Mode: ${mode}`,
"",
"When using tools:",
"- Explain which tool you are calling and why.",
"- If a tool can mutate data, confirm intent first.",
].join("\n");
return {
description: "My reusable assistant rules",
messages: [
{
role: "user",
content: [{ type: "text", text }],
},
],
};
});
// 3) Tool: git_context - fetches compact git context
const GitContextSchema = z.object({
repoPath: z.string().min(1).describe("Absolute path to a git repository"),
maxCommits: z.number().int().min(1).max(50).default(15),
});
server.setRequestHandler(ListToolsRequestSchema, async () => {
return {
tools: [
{
name: "git_context",
description:
"Fetches a compact git context bundle so the assistant stops asking for basic repo details.",
inputSchema: {
type: "object",
properties: {
repoPath: { type: "string", description: "Absolute repo path" },
maxCommits: {
type: "number",
description: "Max commits (1..50)",
default: 15,
},
},
required: ["repoPath"],
},
},
],
};
});
server.setRequestHandler(CallToolRequestSchema, async (request) => {
if (request.params.name !== "git_context") {
throw new Error(`Unknown tool: ${request.params.name}`);
}
const args = GitContextSchema.parse(request.params.arguments);
// Quick guardrail: fail nicely if this isn't a repo.
const isRepo = await execFileAsync("git", [
"-C",
args.repoPath,
"rev-parse",
"--is-inside-work-tree",
])
.then((r) => r.stdout.trim() === "true")
.catch(() => false);
if (!isRepo) {
return {
content: [
{
type: "text",
text: `Not a git repository: ${args.repoPath}`,
},
],
};
}
// Branch
const branch = await execFileAsync("git", [
"-C",
args.repoPath,
"rev-parse",
"--abbrev-ref",
"HEAD",
]).then((r) => r.stdout.trim());
// Recent commits
const commits = await execFileAsync("git", [
"-C",
args.repoPath,
"log",
"-n",
String(args.maxCommits),
"--pretty=format:%h %s",
]).then((r) => r.stdout.trim());
// Diffstat vs latest commit (simple, fast)
const diffstat = await execFileAsync("git", [
"-C",
args.repoPath,
"show",
"--stat",
"--oneline",
"-1",
]).then((r) => r.stdout.trim());
const payload = [
"# Repo Context",
`- Branch: ${branch}`,
"",
"## Recent commits",
commits ? commits.split("\n").map((l) => `- ${l}`).join("\n") : "- None",
"",
"## Latest commit diffstat",
"```",
diffstat,
"```",
].join("\n");
return {
content: [{ type: "text", text: payload }],
};
});
// Boot code for stdio transport
async function main() {
const transport = new StdioServerTransport();
await server.connect(transport);
log("mcp-house-rules running on stdio");
}
main().catch((err) => {
log("Fatal error:", err);
process.exit(1);
});
