Borrowing it
Nothing to install: this file belongs to xyzzylabs/tc39-mcp. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/xyzzylabs/tc39-mcp/main/.github/copilot-instructions.mdgit clone --depth 1 https://github.com/xyzzylabs/tc39-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/instructions/xyzzylabs/tc39-mcp/copilot-instructions)<a href="https://agentmods.dev/instructions/xyzzylabs/tc39-mcp/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/xyzzylabs/tc39-mcp/copilot-instructions/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/xyzzylabs/tc39-mcp/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/xyzzylabs/tc39-mcp/copilot-instructions.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00747 | $0.00747 |
| Opus 5 | $0.00374 | $0.00374 |
| Sonnet 5 | $0.00149 | $0.00149 |
| Haiku 4.5 | $0.00075 | $0.00075 |
Grade A, and why
tc39-mcp copilot-instructions.md 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 8d 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.
How it starts
The opening of the file, as written. The whole thing — 63 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Copilot instructions for tc39-mcp
Guidance for GitHub Copilot — including Copilot code review — in this repository.
The authoritative rules live in AGENTS.md (the
cross-tool agent contract; CLAUDE.md and this file defer to it). Read
it first. The notes below restate the invariants a review should enforce
and flag the patterns that are intentional here, so reviews stay
signal-heavy.
What this project is
A read-only, public MCP server for the TC39 specs (ECMA-262 +
ECMA-402). It exposes structured clauses, AOID-aware search, in+out
cross-references, edition diffs, git history, test262 search, and
proposal lookup over the Model Context Protocol — locally over stdio or
hosted as a Cloudflare Worker over HTTP. Data is SHA-pinned and
auto-refreshes from the upstream tc39/* mains. The server is the
product: code, dependencies, and docs read as if written for any
reader of the TC39 specs, not one downstream consumer.
When reviewing, enforce these invariants
- The tool surface stays narrow. Every tool is read-only, deterministic, and a pure function of SHA-pinned data — no execution, no auth, no writes, no user-supplied code. Flag any new tool or schema change that breaks this.
- Nothing hosted-incompatible in the tool surface. No shell-out,
network call, or filesystem write that can't run behind a Cloudflare
Worker. The only subprocess in the whole server is
spec.history'sgit logagainst a vendored checkout — flag any new one. - Comments and docs describe the code, in general terms. Flag anything that only makes sense to a specific downstream consumer; it should describe the general behavior instead.
- Schemas are the contract. Input schemas use Zod; every exported
interface field carries a JSDoc comment (the
/toolspage is generated from these). A tool-schema change is breaking — flag a missingCHANGELOG.mdentry. docs/tools.mdis generated bynpm run docs:datafrom the schemas — never hand-edited. Flag manual edits.- Tests are co-located as
*.test.ts(worker tests underworker/src/**). A new tool needs a unit test and, after regeneration, adocs/tools.mdsection.
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.
- 8d ago First seen · 63 lines · 747 tokens per session scan A a74b63b808ca
tc39-mcp copilot-instructions.md is an instructions file published in the GitHub repository xyzzylabs/tc39-mcp (2 stars, last pushed yesterday), licensed MIT. It adds 747 tokens to every session, about $0.0037 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.
Other instructions, from other repositories
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AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
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vscode buildNext.instructions.md
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Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, applying the notice (cutover) and fallback chain (never fail the build).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
spec-kit AGENTS.md
AGENTS.md instructions for github/spec-kit, covering agents.md, about spec kit and specify, quickstart — add a new integration in 5 steps, integration architecture and integrationmanifest — file tracking.