The latest articles on DEV Community by ShipStack (@ship_stack). https://dev.to/ship_stack https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F4228124%2F57bdbf95-2f29-4704-a7b6-dfeabded5163.png https://dev.to/ship_stack en ShipStack Thu, 05 Nov 2026 09:26:59 +0000 https://dev.to/ship_stack/stop-cursor-from-rewriting-your-whole-file-a-10-line-project-rule-that-keeps-diffs-small-3lbd https://dev.to/ship_stack/stop-cursor-from-rewriting-your-whole-file-a-10-line-project-rule-that-keeps-diffs-small-3lbd <p>If you use Cursor's agent on a real codebase, you've probably seen it: you ask for a one-line fix and get back a diff that reformats imports, renames variables, and "improves" three functions you didn't touch.</p> <p>The fix that's worked best for me isn't a better prompt — it's a <strong>project rule</strong> that's always applied.</p> <h2> The rule </h2> <p>Create <code>.cursor/rules/small-diffs.mdc</code>:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight yaml"><code><span class="nn">---</span> <span class="na">description</span><span class="pi">:</span> <span class="s2">"</span><span class="s">Keep</span><span class="nv"> </span><span class="s">changes</span><span class="nv"> </span><span class="s">minimal</span><span class="nv"> </span><span class="s">and</span><span class="nv"> </span><span class="s">scoped"</span> <span class="na">alwaysApply</span><span class="pi">:</span> <span class="kc">true</span> <span class="nn">---</span> <span class="pi">-</span> <span class="s">Change only the lines required for the task. Do not reformat, reorder imports, or rename unrelated code.</span> <span class="pi">-</span> <span class="s">Before editing, state in one sentence which files and functions you will touch.</span> <span class="pi">-</span> <span class="s">If a fix needs changes outside that scope, stop and ask first.</span> <span class="pi">-</span> <span class="s">Match the existing style of the file, even if you'd write it differently.</span> <span class="pi">-</span> <span class="s">Never delete comments or tests unless asked.</span> <span class="pi">-</span> <span class="s">Prefer editing existing functions over adding new abstractions.</span> <span class="pi">-</span> <span class="s">After editing, list every file changed and why.</span> </code></pre> </div> <h2> Why it works </h2> <ul> <li> <strong>"State the scope first"</strong> makes the agent commit to a plan you can reject before any edit happens.</li> <li> <strong>"Stop and ask"</strong> turns silent scope creep into a question.</li> <li> <strong>"Match existing style"</strong> kills the reformat-everything diffs that make review painful.</li> <li> <strong>"List every file changed"</strong> gives you a free checklist for review.</li> </ul> <h2> Tips </h2> <ol> <li>Keep always-on rules short. Long rules get diluted; put specialised guidance in rules scoped with <code>globs</code> (e.g. <code>**/*.test.ts</code>) instead.</li> <li>One concern per rule file. Easier to toggle when debugging odd behaviour.</li> <li>Commit <code>.cursor/rules/</code> so your whole team gets the same behaviour.</li> <li>When the agent misbehaves, add one line to a rule rather than repeating yourself in chat.</li> </ol> <h2> Try it </h2> <p>Drop the file in, ask for a small fix, and compare the diff to what you got before. I'd be curious whether it helps on your codebase — tell me in the comments what rule you'd add.</p> <p><em>Disclosure: I'm the author of ShipStack's Cursor Rules + Skills Pack, a paid collection of rules like this one (testing, refactors, PR review, etc.). If this one helped, the rest are here: <a href="https://shipstack.sognia.workers.dev/cursor-pack" rel="noopener noreferrer">https://shipstack.sognia.workers.dev/cursor-pack</a> — but the rule above is free to use however you like.</em></p> cursor ai productivity webdev