diff --git a/AGENTS.md b/AGENTS.md
index 262672de..acde0eb7 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -141,7 +141,10 @@ Usage notes:
 - ALWAYS run `npm run lint` before committing - CI will fail otherwise
 - ALWAYS run `npm run pretty` to format code consistently
 - ESLint configuration in `.eslintrc.json` enforces React/JSX standards
-- Prettier configuration in `.prettierrc` handles formatting
+- Prettier configuration in `.prettierrc` handles formatting (100 char width, no semicolons, single quotes, trailing commas)
+
+✅ Good: `import Browser from 'webextension-polyfill'` (single quotes, no semicolon)
+❌ Bad: `import Browser from "webextension-polyfill";` (double quotes, semicolon)
 
 - Naming conventions: component directories use PascalCase; feature folders use kebab-case; entry files are typically `index.jsx` or `index.mjs`
 - Avoid heavy dependencies; if necessary, justify and keep bundle size under control
@@ -166,6 +169,7 @@ Usage notes:
 - Commit subject: imperative, capitalize first word; separate subject/body with a blank line; wrap at ~72 characters; explain what and why.
 - PRs: link related issues, summarize scope/behavior changes; include screenshots for UI changes.
 - Note i18n updates in PR description when `src/_locales/` changes.
+- If any validation step is skipped, include `Validation skipped: <reason>; <runtime impact or "no runtime files touched">` in the PR description.
 
 ### Directory Structure
 
@@ -204,7 +208,7 @@ src/
 
 ## Localization
 
-- Source of truth: `src/_locales/en/main.json`; do not change keys
+- Source of truth: `src/_locales/en/main.json`; do not change existing keys (only add new ones)
 - Add new strings to `en/main.json` first, then propagate to other locales
 - Register new locales in `src/_locales/resources.mjs`
 - Preserve placeholders and product names; keep punctuation/quotes intact
@@ -240,6 +244,8 @@ The extension supports multiple AI providers:
 - Updating API integration: Modify files in `src/services/apis/`
 - Adding new UI component: Create in `src/components/`
 
+**Note:** Ask before deleting/renaming files, modifying build config/manifests, or making changes that affect multiple site adapters. If the user explicitly requests one of these changes, proceed and document scope and risk in the PR summary.
+
 ## Time Expectations
 
 - Do not interrupt builds or long-running commands unless they appear hung or unresponsive.
@@ -252,12 +258,10 @@ The extension supports multiple AI providers:
 
 ## Critical Validation Steps
 
-1. ALWAYS run `npm run build` after any code changes
-2. ALWAYS manually load and test the built extension in a browser (no automated testing available)
-3. ALWAYS verify the build creates expected file structure (non-empty bundles, no missing files)
-4. ALWAYS test core extension functionality (popup, content script injection, keyboard shortcuts)
-
-Always build and manually test the extension in a browser before considering any change complete. Simply running the build is NOT sufficient - you must load the extension and test actual functionality.
+1. Runtime-impacting changes (`src/**`, `src/manifest*.json`, `build.mjs`, `package*.json`, `safari/**`): run `npm run build`, verify expected build artifacts, and run manual browser smoke tests.
+2. Behavior-adjacent localization changes (`src/_locales/**` only): run `npm run build` and manual browser smoke tests.
+3. Docs-only changes (`*.md`, `screenshots/**`): build/manual browser tests may be skipped, but the PR description must include `Validation skipped: docs-only change; no runtime files touched`.
+4. When in doubt, treat the change as runtime-impacting and execute the full validation flow.
 
 ---