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.
npx agentmods add rules/bowen31337/expressjs_mcp/mcp-conventionsgit clone --depth 1 https://github.com/bowen31337/expressjs_mcpWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/rules/bowen31337/expressjs_mcp/mcp-conventions)<a href="https://agentmods.dev/rules/bowen31337/expressjs_mcp/mcp-conventions"><img src="https://agentmods.dev/badge/rules/bowen31337/expressjs_mcp/mcp-conventions.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00006 | $0.00311 |
| Opus 5 | $0.00003 | $0.00156 |
| Sonnet 5 | $0.00001 | $0.00062 |
| Haiku 4.5 | $0.00001 | $0.00031 |
Grade A, and why
mcp-conventions 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 4d ago.
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.
What it actually says
MCP Tool Conventions
Tool Naming
title: Human-readable format like"GET /users"name: Safe identifier format like"GET_/users"(spaces → underscores)
Schema Structure
Tools must have consistent schema structure:
{
name: string, // Safe identifier
title: string, // Human readable
description: string, // What the tool does
inputSchema: object, // JSON Schema for input
outputSchema: object, // JSON Schema for output
examples: any[], // Usage examples
route: { method, path } // Original Express route info
}
HTTP Gateway Endpoints
GET /mcp/tools- List all available toolsPOST /mcp/invoke- Invoke a tool with{ toolName, args }
Response Format
Invocation responses follow this pattern:
// Success
{ ok: true, result: any, status: number }
// Error
{ ok: false, error: string }
Schema Priority
- Per-route zod annotations (
schemaAnnotations) - OpenAPI v3 specification (
openapioption) - Permissive fallback (
{ type: 'object', additionalProperties: true })
Auth Integration
- Reuse existing Express middleware chain
- No bypass of authentication/authorization
- Preserve 401/403 responses from middleware
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.
- 4d ago First seen · 47 lines · 6 tokens per session scan A 27b6e93a027a
mcp-conventions is a cursor rule published in the GitHub repository bowen31337/expressjs_mcp (1 stars, last pushed 1y ago), licensed MIT. It adds 6 tokens to every session and 311 once invoked, about $0.0000 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.
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