Harper MCP

Harper MCP

Guidelines for exposing a Harper instance as a Model Context Protocol (MCP) server and for building the tools, prompts, and resources AI clients consume. Harper implements MCP Streamable HTTP (spec rev 2025-06-18) with two independent profiles: application (your app's surface) and operations (Harper administration).

When to Use

Reference these guidelines when:

• Enabling or configuring the MCP endpoint on a Harper instance
• Connecting an MCP client (Claude, agent frameworks, custom HTTP code) to Harper
• Deciding what tools an AI should see for a schema, or trimming that surface
• Exposing custom behavior (mcpTools), prompt templates (mcpPrompts), or content (mcpResources) to AI clients
• Protecting a public or anonymous-accessible MCP endpoint (rate limits, durable quotas, hardening)
• Debugging MCP wire errors (session/protocol headers, 400s, SSE)

How It Works

1. Start with enabling-mcp to mount a profile, then connecting-clients for the handshake contract.
2. For the tool surface, consult automatic-verb-tools first — most CRUD needs are covered with zero code — and reach for custom-mcp-tools only for real behavior.
3. For content and templates, use custom-mcp-resources and custom-mcp-prompts; resources-surface explains what exists without any code.
4. Before any public exposure, work through security-posture's checklist and configure rate-limiting (+ durable-quotas for cost-bearing tools).

Examples

See the concrete examples embedded in each rule (curl handshakes, static mcpTools/mcpResources declarations, quota-hook implementations, and hardening configs).

Rule Categories by Priority

Quick Reference

1. Setup & Connection (HIGH)

• enabling-mcp — How to enable and configure Harper's MCP server profiles (application and operations).
• connecting-clients — How MCP clients connect to Harper - the initialize handshake, session and protocol-version headers, and authentication.

2. Tools & Prompts (HIGH)

• automatic-verb-tools — How Harper auto-generates CRUD MCP tools from exported tables, with RBAC filtering and allow/deny/maxTools controls.
• custom-mcp-tools — How to expose custom instance methods as MCP tools via static mcpTools, including the anonymous-exposure security model.
• custom-mcp-prompts — How to publish reusable prompt templates to MCP clients via static mcpPrompts.

3. Resources (MEDIUM)

• resources-surface — The MCP resources surface - harper:// metadata URIs, harper+rest:// table descriptors, templates, subscriptions, and list_changed notifications.
• custom-mcp-resources — How to serve custom content (docs pages, reports, binaries) as MCP resources via static mcpResources with URI templates and completions.

4. Operations & Security (HIGH)

• rate-limiting — MCP tools/call rate limiting - per-tool, per-session, and per-client-identity token buckets, and the identityHeader trust model.
• durable-quotas — Operator-pluggable durable quotas for MCP tools/call via the server.setMcpQuotaHandler registration hook, with a race-safe counter pattern.
• security-posture — The MCP security model - anonymous access, RBAC boundaries, origin validation, audit logging, and the hardening checklist for public instances.

How to Use

Read individual rule files for detailed explanations and code examples:

rules/enabling-mcp.md
rules/connecting-clients.md
rules/custom-mcp-tools.md
rules/custom-mcp-resources.md
rules/security-posture.md

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md