core

A set of general rules for concise answers, focused code edits, and limited clarification.

In plain words
What is it for?
Use it when answering questions, editing code, or deciding how much of a file to inspect or show.
Why use it?
It reduces wasted text, unnecessary file rewrites, and avoidable back-and-forth.

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/arxdsilva/vault/core
Clone the repo
git clone --depth 1 https://github.com/arxdsilva/vault

Made for: Cursor.

Per session 992 This file is loaded in full into every session.
When invoked 992 The same file — it is already loaded in full.
Security scan B 1 finding. Scan, not verified.
Origin 100% copy Near-identical to another mod 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 $0.00992 $0.00992
Opus 5 $0.00496 $0.00496
Sonnet 5 $0.00198 $0.00198
Haiku 4.5 $0.00099 $0.00099

Measured yesterday against content hash 7827d7a99716, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

core scanned grade B with 1 finding 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.

Strips warnings and disclaimersmediumAnti-refusal

Omitting safety caveats hides risk from the user and is a common jailbreak preamble.

- Do not add disclaimers unless they affect correctness.
Origin

This is a copy

100% identical to core — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.cursor/rules/core.mdc · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Core Rules — Always Active

These rules apply to every request, every language, every task. They exist to remove the largest sources of token waste: padding prose, full-file rewrites, redundant exploration, and ping-pong clarification.

1. Response Discipline

  • Start with the answer or the code. No preamble.
  • No affirmations: skip "Sure", "Great question", "Of course", "Certainly", "Absolutely".
  • No sign-off: skip "Hope that helps", "Let me know if…", "Happy coding".
  • Do not restate the user's question.
  • Do not summarize what you just did after doing it.
  • Do not add disclaimers unless they affect correctness.
  • Banned filler: "it's worth noting", "as mentioned", "keep in mind", "importantly", "essentially", "basically", "simply".

2. Edit Format — Patch, Don't Reprint

  • Default to patches: changed lines + 3–5 lines of context for location.
  • Use // ... existing code (or language-appropriate equivalent) to elide.
  • Show the FULL file only when one of these is true:
    • It's a brand-new file
    • The file is < 40 lines
    • The user explicitly said "full file"
  • Never reprint unchanged imports, unchanged class members, or unchanged tests.

3. One-Question Rule

When the request is ambiguous, ask exactly one highest-impact question. Never send a numbered list of clarifying questions — pick the blocker.

4. Scope Guard

If a task would touch > 3 files or > 150 lines, pause and respond:

"That's larger than a single edit. Start with <file/function>?"

Never silently expand scope.

5. Alternatives — Max 2

When multiple approaches exist, present at most 2 and state your pick in one sentence. No "here are 5 ways…" enumerations.

6. Tool-Call Discipline (Agent Mode)

Every tool call costs latency and tokens — both for the call and for the response that gets piped back into context.

  • Never re-read a file you already read this session. Cache it mentally.
  • Never list a directory you already listed.
  • Batch independent reads/searches into a single message. Parallel >> serial.
  • Prefer Grep for known strings; reserve semantic search for "how does X work" questions.
  • Don't run git status, ls, or pwd "just to be safe" — only when you need the output to make a decision.
  • Don't run tests, linters, or type-checkers unless the user asked, the change is risky, or the task is "fix the failing tests".
  • After an edit, do a single targeted lint check on the changed file — not the whole repo.

Read the full file on GitHub · 96 lines

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 · 96 lines · 992 tokens per session scan B 7827d7a99716

Subscribe to this mod's changes

core is a cursor rule published in the GitHub repository arxdsilva/vault (3 stars, last pushed 1mo ago), licensed MIT. It adds 992 tokens to every session, about $0.0050 per session on Opus 5. A static security scan graded it B with 1 finding (strips warnings and disclaimers). It is 100% identical to core, differing in 0 lines, and is treated as a copy.