Effect TS

What it does

When your agent uses it

• Refactoring TypeScript code that uses Effect — when you see imports from effect
• Any @effect/ scoped package (schema
• The user asks about Effect patterns
• Migration from Promises/fp-ts/neverthrow to Effect

Example prompts

• “s useEffect, Redux side effects, or general English usage of”
• “/effect-ts”

What it can do on your machine

Read from SKILL.md and the folder at commit cf93c57. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are typescript).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Effect TS loads about 2k tokens when it runs, and up to ~392k if it reads all its reference files. Until then it costs about 235 tokens; SKILL.md has 399 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~235

When it runs · the whole SKILL.md, loaded when a task matches

~2k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~392k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from pproenca/dot-skills at commit cf93c57, republished under its MIT licence (© pproenca). 399 words, ~1,963 tokens.

name

effect-ts

description

Effect-TS library usage in TypeScript — Effect.gen generators, Schema.Struct/Schema.Class definitions, Layer/Context.Tag/Service patterns, Effect.pipe pipelines, Data.TaggedError/Data.Class error types, Ref/Queue/PubSub/Deferred concurrency primitives, Match module, Config providers, Scope/Exit/Cause/Runtime patterns, or any code using Effect's typed error channel (E parameter). Trigger when writing, reviewing, debugging, or refactoring TypeScript code that uses Effect — when you see imports from `effect`, `effect/*`, or any `@effect/*` scoped package (schema, platform, sql, opentelemetry, cli, cluster, rpc, vitest). Also trigger when the user asks about Effect patterns, migration from Promises/fp-ts/neverthrow to Effect, or how to structure an Effect application. Do NOT trigger for React's useEffect, Redux side effects, or general English usage of "effect" unless the context clearly involves the Effect-TS library.

//         ┌─── Success type
//         │        ┌─── Error type
//         │        │      ┌─── Required dependencies
//         ▼        ▼      ▼
Effect<Success, Error, Requirements>

import { Effect } from "effect"

// From sync values
const succeed = Effect.succeed(42)
const fail = Effect.fail(new Error("oops"))

// From sync code that may throw
const sync = Effect.try(() => JSON.parse(data))

// From promises
const async = Effect.tryPromise(() => fetch(url))

// From generators (recommended for complex flows)
const program = Effect.gen(function* () {
  const user = yield* getUser(id)
  const todos = yield* getTodos(user.id)
  return { user, todos }
})

// Async (returns Promise)
Effect.runPromise(program)

// With full Exit information
Effect.runPromiseExit(program)

// Sync (throws on async)
Effect.runSync(program)

import { Data, Effect } from "effect"

class NotFound extends Data.TaggedError("NotFound")<{
  readonly id: string
}> {}

class Unauthorized extends Data.TaggedError("Unauthorized")<{}> {}

// Error type is tracked: Effect<User, NotFound | Unauthorized>
const getUser = (id: string) =>
  Effect.gen(function* () {
    // ...
  })

import { Context, Effect, Layer } from "effect"

// Define a service
class UserRepo extends Context.Tag("UserRepo")<
  UserRepo,
  { readonly findById: (id: string) => Effect.Effect<User, NotFound> }
>() {}

// Use in effects — adds to Requirements channel
const program = Effect.gen(function* () {
  const repo = yield* UserRepo
  return yield* repo.findById("1")
})

// Implement with a Layer
const UserRepoLive = Layer.succeed(UserRepo, {
  findById: (id) => Effect.succeed({ id, name: "Alice" })
})

// Provide and run
program.pipe(Effect.provide(UserRepoLive), Effect.runPromise)

import { Schema } from "effect"

const User = Schema.Struct({
  id: Schema.Number,
  name: Schema.String,
  email: Schema.String.pipe(Schema.pattern(/@/))
})

type User = typeof User.Type

// Decode (parse + validate)
const decode = Schema.decodeUnknownSync(User)
const user = decode({ id: 1, name: "Alice", email: "a@b.com" })

import { Effect, pipe } from "effect"

// Data-last (pipe style)
const result = pipe(
  getTodos,
  Effect.map((todos) => todos.filter((t) => !t.done)),
  Effect.flatMap((active) => sendNotification(active.length)),
  Effect.catchTag("NetworkError", () => Effect.succeed("offline"))
)

// Fluent (method style)
const result2 = getTodos.pipe(
  Effect.map((todos) => todos.filter((t) => !t.done)),
  Effect.flatMap((active) => sendNotification(active.length))
)

© pproenca, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 23 other files (references) in skills/.experimental/effect-ts of pproenca/dot-skills.

• SKILL.md
• gotchas.md
• metadata.json
• references/_sections.md
• references/ai-integration.md
• references/code-style.md
• references/conc-concurrency.md
• references/core-concepts.md
• references/data-types.md
• references/error-management.md
• references/getting-paradigm.md
• references/getting-started.md
• references/micro-module.md
• references/migration-guides.md
• references/obs-observability.md
• references/plat-platform.md
• references/req-management.md
• references/resource-management.md
• references/sched-scheduling.md
• references/schema-advanced.md
• … and 4 more

Open the folder on GitHubat commit cf93c57