effect-composition

A set of coding rules for composing Effect layers, avoiding problematic Effect service patterns, applying Biome checks, and writing mocks. Effect is a TypeScript library for managing services and errors; Biome is a code-quality tool.

In plain words
What is it for?
Use it when writing or reviewing TypeScript code that uses Effect layers and services, Biome, or mocks.
Why use it?
It gives an agent specific guidance for keeping Effect-based code consistent and for avoiding service and mocking patterns the author considers problematic.

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/pauljphilp/effectiveagent/effect-composition
Clone the repo
git clone --depth 1 https://github.com/PaulJPhilp/EffectiveAgent

Made for: Cursor.

Per session 209 This file is loaded in full into every session.
When invoked 209 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00209 $0.00209
Opus 5 $0.00105 $0.00105
Sonnet 5 $0.00042 $0.00042
Haiku 4.5 $0.00021 $0.00021

Measured 2d ago against content hash d902db054c22, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

effect-composition 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 2d 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.

.cursor/rules/effect/effect-composition.mdc · 16 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. 2d ago First seen · 16 lines · 209 tokens per session scan A d902db054c22

Subscribe to this mod's changes

effect-composition is a cursor rule published in the GitHub repository PaulJPhilp/EffectiveAgent (11 stars, last pushed 9mo ago), with no licence file. It adds 209 tokens to every session, about $0.0010 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 2026-08-30.