A bounded JSFX authoring and validation guide for Pulp. JSFX is a scripting format used for audio effects in REAPER, and this guide covers only the listed supported sections rather than full REAPER compatibility.

Use it to validate .jsfx source files and create audio examples using @init, @slider, @block, and @sample; files using @gfx are outside its scope.

It makes the current support boundary clear and catches files that use unsupported features instead of implying they will run everywhere.

jsfx-subset — Skill for Claude Code by Generous-Corp: A bounded JSFX authoring and validation guide for Pulp.

Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo

git clone --depth 1 https://github.com/Generous-Corp/pulp

agentmods

npx agentmods add skills/generous-corp/pulp/jsfx-subset

Made for: Claude Code.

Or install pulp, the plugin that ships this one along with the rest of its 63 skills, 30 commands, 3 hooks, 1 MCP server.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/generous-corp/pulp/jsfx-subset.svg)](https://agentmods.dev/skills/generous-corp/pulp/jsfx-subset)

Your own site

<a href="https://agentmods.dev/skills/generous-corp/pulp/jsfx-subset"><img src="https://agentmods.dev/badge/skills/generous-corp/pulp/jsfx-subset.svg" alt="Measured on agentmods" height="20"></a>

Per session 31 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 620 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.

Model	Per session	Once invoked
Fable 5.1	$0.00031	$0.00620
Opus 5	$0.00015	$0.00310
Sonnet 5	$0.00006	$0.00124
Haiku 4.5	$0.00003	$0.00062

Measured yesterday against content hash c909f0ae652a, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

jsfx-subset 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.

.agents/skills/jsfx-subset/SKILL.md · 92 lines

How it starts

The opening of the file, as written. The whole thing — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.

JSFX Bounded Subset

Use this skill when a task involves Pulp's current JSFX support lane.

Truthful Position

Pulp supports a bounded audio-focused JSFX authoring lane, not full REAPER parity.

Supported now:

.jsfx source files
subset validation for @init, @slider, @block, @sample
slider declarations slider1..slider64
source-only examples that stay inside that subset

Not supported by this skill:

@gfx
file I/O
silent compatibility assumptions with REAPER
a shipped JSFX runtime/engine in Pulp core

Core Files

docs/guides/jsfx.md
tools/scripts/jsfx_subset.py
examples/jsfx-gain/
examples/jsfx-tremolo/
examples/jsfx-delay/

Recommended Workflow

1. Validate the file first

python3 tools/scripts/jsfx_subset.py doctor \
  --file examples/jsfx-gain/PulpJsfxGain.jsfx

Use --json when another tool or script needs structured output.

2. Stay inside the bounded subset

Allowed sections today:

@init
@slider
@block
@sample

If a file uses @gfx or another unsupported section, treat that as an explicit out-of-scope failure, not a bug in the validator.

3. Keep docs truthful

When updating this lane, keep these in sync:

docs/guides/jsfx.md
docs/reference/capabilities.md
docs/guides/examples.md
planning/v3-phase14-gap-closure-status.md

What To Check

For the current JSFX lane, verify:

desc: exists
slider declarations are sane and unique
unsupported sections fail clearly
docs do not imply full REAPER JSFX compatibility or a shipped runtime

Gotchas

Section directives can carry trailing arguments. REAPER documents @gfx WIDTH HEIGHT as the standard form for declaring the preferred plugin window size. Any future regex change to SECTION_PATTERN in tools/scripts/jsfx_subset.py must keep matching the @name <args> shape — anchoring to end-of-line silently lets @gfx 200 200 slip past the bounded-subset check (the exact bug the 2026-05-26 follow-up fixed). Regression coverage lives in tools/scripts/test_jsfx_subset.py::test_doctor_rejects_gfx_section_with_size_directive.

Read the full file on GitHub · 92 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.

yesterday First seen · 92 lines · 31 tokens per session scan A c909f0ae652a

Subscribe to this mod's changes

jsfx-subset is a skill published in the GitHub repository Generous-Corp/pulp (16 stars, last pushed yesterday), licensed MIT. It adds 31 tokens to every session and 620 once invoked, about $0.0002 per session on Opus 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 2026-09-04.

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