mcp-surface

A set of rules for an MCP gateway, a service that gives coding agents access to tools. It keeps the gateway small, makes agents check available capabilities first, and uses live descriptions as the source of truth.

In plain words
What is it for?
For designing and maintaining MCP tools, capability checks, bytecode simulation access, validation schemas, builds, and related documentation.
Why use it?
It prevents the gateway from filling up with separate tools for every protocol feature and reduces errors caused by outdated documentation or unsupported requests.

Cursor rule for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/feelyourprotocol/mcp-gateway/mcp-surface
Clone the repo
git clone --depth 1 https://github.com/feelyourprotocol/mcp-gateway

Made for: Cursor.

Per session 309 This file is loaded in full into every session.
When invoked 309 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00309 $0.00309
Opus 5 $0.00154 $0.00154
Sonnet 5 $0.00062 $0.00062
Haiku 4.5 $0.00031 $0.00031

Measured yesterday against content hash e0dafc26808c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mcp-surface scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/rules/mcp-surface.mdc · 36 lines

What it actually says

MCP surface (gateway)

Few generic tools

  • Tools are verbs (probe, simulate, later generate), not per-EIP endpoints
  • Do not add simulate_eip8024 or similar — EIP modules live in the engine catalog
  • New query shape → one new generic tool + engine function

Descriptions are the prompt

  • Tool description strings must mention Amsterdam, runnable EIPs, and caller-supplied bytecode
  • describe_capabilities: probe first — forks, runnable modules, opcodes/encoding
  • run_evm_bytecode: point at probe; no demo programs shipped

Probe-first for runtime agents

  • Human and runtime agents should call describe_capabilities before simulate
  • Live describeCapabilities() is authoritative — not stale markdown in the repo

After gateway changes

  1. npm run build in mcp-gateway
  2. npm run build in mcp-execution-engine if engine API changed
  3. Restart MCP server in Cursor (Settings → MCP)
  4. Update mcp-docs tool pages + llms.txt when behavior or tool list changes

Schemas

  • Zod in src/schemas/ — source of truth for validation
  • Copy JSON schema to website/mcp-docs/public/schemas/ when inputs change
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 36 lines · 309 tokens per session scan A e0dafc26808c

Subscribe to this mod's changes

mcp-surface is a cursor rule published in the GitHub repository feelyourprotocol/mcp-gateway (0 stars, last pushed yesterday), licensed MIT. It adds 309 tokens to every session, about $0.0015 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.