What is effect-best-practices?

A coding guide for Effect-TS, a TypeScript library for describing computations, errors, and dependencies, plus effect-atom React components. It sets patterns for services, typed errors, dependency layers, composition, and schema imports.

Use it when writing or reviewing Effect.Service, Schema.TaggedError, Layer composition, or effect-atom React code, especially when composing operations with pipe and handling typed errors.

It keeps Effect-TS code consistent and makes errors and dependencies explicit. It also prevents use of the deprecated @effect/schema package.

effect-best-practices — Skill for Claude Code and Codex by betalyra

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.

Any agent

npx skills add betalyra/effect-skills --skill effect-best-practices

Clone the repo

git clone --depth 1 https://github.com/betalyra/effect-skills

Made for: Claude Code, Codex.

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/betalyra/effect-skills/effect-best-practices/github.svg)](https://agentmods.dev/skills/betalyra/effect-skills/effect-best-practices)

Your own site

<a href="https://agentmods.dev/skills/betalyra/effect-skills/effect-best-practices"><img src="https://agentmods.dev/badge/skills/betalyra/effect-skills/effect-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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/betalyra/effect-skills/effect-best-practices"><img src="https://agentmods.dev/badge/skills/betalyra/effect-skills/effect-best-practices.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 45 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,743 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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	$0.00045	$0.03743
Opus 5.5	$0.00018	$0.01497
Sonnet 5.5	$0.00009	$0.00749
Haiku 4.5	$0.00005	$0.00374

Measured 2mo ago against content hash b53b6903a438, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

effect-best-practices 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 2mo 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.

effect-best-practices/SKILL.md · 482 lines

How it starts

The opening of the file, as written. The whole thing — 482 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Effect-TS Best Practices

This skill enforces opinionated, consistent patterns for Effect-TS codebases. These patterns optimize for type safety, testability, observability, and maintainability.

Core Principles

Effect Type Signature

Effect<Success, Error, Requirements>
//      ↑        ↑       ↑
//      |        |       └── Dependencies (provided via Layers)
//      |        └── Expected errors (typed, must be handled)
//      └── Success value

Data-First Piped Style

ALWAYS prefer data-first pipe style for composition:

// ✅ GOOD: Data-first with pipe
const result = value.pipe(
  Effect.map((n) => n * 2),
  Effect.flatMap((n) => processValue(n)),
  Effect.catchTag("NetworkError", () => Effect.succeed(fallback)),
);

// ❌ BAD: Function-first style
const result = Effect.catchTag(
  Effect.flatMap(
    Effect.map(value, (n) => n * 2),
    (n) => processValue(n),
  ),
  "NetworkError",
  () => Effect.succeed(fallback),
);

"@effect/schema" is deprecated

Don't try to install nor import from "@effect/schema", it is deprecated. Instead just import from "effect" package.

// ✅ GOOD
import { Schema } from "effect";

// ❌ BAD
import { Schema } from "@effect/schema";

Quick Reference: Critical Rules

Category	DO	DON'T
Services	`Effect.Service`	`Context.Tag` for business logic
Dependencies	`dependencies: [Dep.Default]` at the top of the service	Manual `Layer.provide` at usage sites
Errors	`Schema.TaggedError` with `message` and `cause` fields	Plain classes or generic Error
Error Specificity	`UserNotFoundError`, `SessionExpiredError`	Generic `NotFoundError`, `BadRequestError`
Error Handling	`catchTag` (supports multiple tags) / `catchTags`	`catchAll` or `mapError`
IDs	`Schema.UUID.pipe(Schema.brand("@App/EntityId"))`	Plain `string` for entity IDs
Functions	`Effect.fn("Service.method")`	Anonymous generators
Logging	`Effect.log` with structured data	`console.log`
Config	`Config.*` with validation	`process.env` directly
Options	`Option.match` with both cases	`Option.getOrThrow`
Nullability	`Option<T>` in domain types	`null`/`undefined`
Atoms	`Atom.make` outside components	Creating atoms inside render
Atom State	`Atom.keepAlive` for global state	Forgetting keepAlive for persistent state
Atom Updates	`useAtomSet` in React components	`Atom.update` imperatively from React
Atom Cleanup	`get.addFinalizer()` for side effects	Missing cleanup for event listeners
Atom Results	`Result.builder` with `onErrorTag`	Ignoring loading/error states

Read the full file on GitHub · 482 lines

Files

What ships with it

11 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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.

2mo ago First seen · 482 lines · 45 tokens per session scan A b53b6903a438

Subscribe to this mod's changes

effect-best-practices is a skill published in the GitHub repository betalyra/effect-skills (20 stars, last pushed 3mo ago), licensed MIT. It adds 45 tokens to every session and 3,743 once invoked, about $0.0002 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.

Frontend Languages React TypeScript effect effect-ts skills skills-sh

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