Visual Studio Code is a code editor that supports editing, navigating, understanding, debugging, and extending software projects. Developers use it for the edit-build-debug cycle, and the catalogue add-ons provide skills, instructions, and agents for working within the editor.
Borrowing it
Nothing to install: this file belongs to microsoft/vscode. 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/microsoft/vscode/main/.github/instructions/css-best-practices.instructions.mdgit clone --depth 1 https://github.com/microsoft/vscodeWrote 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/microsoft/vscode/css-best-practices)<a href="https://agentmods.dev/instructions/microsoft/vscode/css-best-practices"><img src="https://agentmods.dev/badge/instructions/microsoft/vscode/css-best-practices/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/microsoft/vscode/css-best-practices"><img src="https://agentmods.dev/badge/instructions/microsoft/vscode/css-best-practices.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 | $0.00305 | $0.00305 |
| Opus 5.5 | $0.00122 | $0.00122 |
| Sonnet 5.5 | $0.00061 | $0.00061 |
| Haiku 4.5 | $0.00030 | $0.00030 |
Grade A, and why
vscode css-best-practices.instructions.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
CSS Best Practices
Selectors
- Avoid
:has()selectors. Because their result depends on descendant state, DOM mutations can invalidate styles on ancestors and cause expensive style recalculation, especially when selectors are broadly scoped. Instead, represent the state explicitly with a class or data attribute on the smallest container you own, and scope selectors to that marker. Add and remove the marker together with the state it represents. - Never add a new match on the
classattribute by substring ([class*="…"],[class^="…"],[class$="…"]). A single such selector anywhere in the workbench stylesheet defeats Blink's per-class invalidation: everyclassListchange then forces a style recalculation for that element, even when no rule references the class that changed. Measured on a 3.7k-node workbench, the ten[class*="monaco-decoration-itemColor"]selectors in the Modern UI tab styles alone made a full style recalculation 2.4x slower. When a class carries a generated suffix, have the code that applies it also set a stable marker class (seeDECORATION_LABEL_COLOR_CLASS) and match that instead. Existingcodicon-*substring selectors are a grandfathered compatibility contract and must only be changed in a dedicated, separately validated codicon migration.
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.
- 1mo ago Changed · +33 tokens per session 9b48526e10b1
- 1mo ago First seen · 12 lines · 272 tokens per session scan A 92e9835ddb8c
vscode css-best-practices.instructions.md is an instructions file published in the GitHub repository microsoft/vscode (193,657 stars, last pushed today), licensed MIT. It adds 305 tokens to every session, about $0.0012 per session on Opus 5.5. 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 2026-08-30.
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