swc-plugin

A set of development notes for building an SWC plugin. SWC is a fast tool that transforms and compiles JavaScript and TypeScript code.

In plain words
What is it for?
Use it to understand the expected SWC plugin design and to run or update its test fixtures.
Why use it?
It points developers to the plugin specification and the project’s test process, reducing uncertainty when changing plugin behavior.

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/vercel/workflow/swc-plugin
Clone the repo
git clone --depth 1 https://github.com/vercel/workflow

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 87 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found 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 $0.00000 $0.00087
Opus 5 $0.00000 $0.00044
Sonnet 5 $0.00000 $0.00017
Haiku 4.5 $0.00000 $0.00009

Measured yesterday against content hash e2bf93ea5d66, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

swc-plugin 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 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.

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.

.cursor/rules/swc-plugin.mdc · 10 lines

What it actually says

SWC plugin development notes

The specification for how to plugin is meant to work can be found in spec.md.

To test the plugin, run pnpm test inside swc-plugin-workflow. If changes have been made, use UPDATE=1 pnpm test to have the fixtures be updated to pass the tests.

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 · 10 lines · 0 tokens per session scan A e2bf93ea5d66

Subscribe to this mod's changes

swc-plugin is a cursor rule published in the GitHub repository vercel/workflow (2,363 stars, last pushed 3d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 87 tokens. 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.