es-toolkit is a JavaScript utility library providing commonly used functions such as debouncing, delaying, chunking, summing, and selecting values, with TypeScript types and a compatibility layer for Lodash. JavaScript and TypeScript developers use it when they need utility code with small bundles and performance-focused implementations, while the catalogue skills support AI coding tools working with the library.
Borrowing it
Nothing to install: this file belongs to toss/es-toolkit. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/toss/es-toolkit/main/AGENTS.mdgit clone --depth 1 https://github.com/toss/es-toolkitWrote 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.
[](https://agentmods.dev/instructions/toss/es-toolkit/agents-md)<a href="https://agentmods.dev/instructions/toss/es-toolkit/agents-md"><img src="https://agentmods.dev/badge/instructions/toss/es-toolkit/agents-md/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.
<a href="https://agentmods.dev/instructions/toss/es-toolkit/agents-md"><img src="https://agentmods.dev/badge/instructions/toss/es-toolkit/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.02089 | $0.02089 |
| Opus 5.5 | $0.00836 | $0.00836 |
| Sonnet 5.5 | $0.00418 | $0.00418 |
| Haiku 4.5 | $0.00209 | $0.00209 |
Grade A, and why
es-toolkit AGENTS.md 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 152 lines — stays where its author put it; the contents beside it link to each section on GitHub.
es-toolkit LLM coding agent instructions
This file gives LLM coding agents the context they need to contribute to es-toolkit. Read it before making changes, and follow it together with .github/CONTRIBUTING.md (and its translations).
Project overview
es-toolkit is a modern, high-performance JavaScript utility library with a small bundle size and strong type annotations. It provides a curated set of utilities that are difficult to write with built-in JavaScript methods but are commonly needed in real-world projects, such as delay, windowed, keyBy, mapValues, camelCase, and toSnakeCaseKeys.
The library is split into two entry points:
es-toolkit— the strict, opinionated main library. Focused on the 85% use case with a simple interface, no complex options, and modern JavaScript semantics.es-toolkit/compat— a Lodash-compatible variant intended to make migration from Lodash easy. Compat is feature-complete; only behavior fixes against Lodash are accepted, not new functions.
es-toolkit is a zero-dependency library and ships with no runtime dependencies.
Development environment
- Primary environment: Node.js v24 (see
.nvmrcfor the exact version) - Recommended editor: Visual Studio Code
- Package manager: Yarn v4, installed via Corepack. See the package manager section in CONTRIBUTING.md for details.
To get started:
corepack enable
yarn install
Common commands:
yarn vitest run # Run all tests
yarn vitest run src/array/chunk # Run tests for a specific function
yarn lint # ESLint
tsc --noEmit # Typecheck
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.
- 1mo ago First seen · 152 lines · 2,089 tokens per session scan A 06a16c14cc06
es-toolkit AGENTS.md is an instructions file published in the GitHub repository toss/es-toolkit (11,378 stars, last pushed yesterday), licensed MIT. It adds 2,089 tokens to every session, about $0.0084 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.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
deno copilot-instructions.md
Copilot instructions for denoland/deno, covering deno development guide for github copilot, network access, high level overview, key directories and key files to understand first.