# Yagni

> Use the moment you reach for more than the task needs — a new abstraction, interface, config knob, or dependency, or anything kept \"for later\" — OR when the simple path tempts you to under-deliver: a stub, a TODO, or the smallest diff that patches a symptom while a sibling caller stays broken. Build only what the task needs, and make it run. Distinct from test-driven-development, which proves c…

- **Type:** Skill
- **Install:** `agentstack add skill-njoyimpeguy-augments-yagni`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [NjoyimPeguy](https://agentstack.voostack.com/s/njoyimpeguy)
- **Installs:** 0
- **Category:** [AI & ML](https://agentstack.voostack.com/c/ai-and-ml)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [NjoyimPeguy](https://github.com/NjoyimPeguy)
- **Source:** https://github.com/NjoyimPeguy/augments/tree/main/skills/common/yagni

## Install

```sh
agentstack add skill-njoyimpeguy-augments-yagni
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# YAGNI — build only what's needed, and make it work

You Ain't Gonna Need It: the cheapest code is the code you never write. But "less code" measures **design**, never **correctness or effort** — a smaller solution that doesn't solve the task isn't lean, it's *unfinished*. This is a discipline skill: under pressure you'll reach for the smallest diff, and the point is to keep that reflex aimed at *scope*, not at *finishing*.

## The one definition everything hangs on

**"Needed" = solves the task the user actually asked for, and runs.** Cutting scope is YAGNI. Cutting *behaviour the task requires* is under-delivery wearing YAGNI as a costume.

## Make the correct path the lazy path

"Be thorough" doesn't hold under pressure. Instead, see the shortcut's *real* cost: a stub is not less work — it's deferred work, plus the bug it ships, plus re-reading all this context when you come back to it. **Doing it right once is the lazier path.** Aim the laziness instinct at the complete solution instead of fighting it.

## The ladder — stop at the first rung that holds

1. **Does it need to exist at all?** Speculative need → skip it, say so in one line.
2. **Already in this codebase?** Reuse it — re-implementing what's a few files over is the most common waste.
3. **Standard library?** Use it.
4. **Native platform feature?** A built-in over a dependency; a constraint over hand-rolled code.
5. **An already-installed dependency?** Use it. Never add one for what a few lines do.
6. **One line?** One line.
7. **Only then:** the minimum code that *fully works*.

No unrequested abstraction: no interface with one implementation, no factory for one product, no config for a value that never changes.

## The ladder runs AFTER comprehension, never instead of it

Read the task and the code it touches; trace the real flow end to end; *then* minimise. The smallest change in the wrong place isn't lazy — it's a second bug. A bug fix targets the **root cause**: fix the shared function every caller routes through once — that is a *smaller* diff than one patch per caller, and patching only the named path leaves siblings broken. (Pair with `debugging`.)

## When you're tempted to call it done

| The thought | The reality |
| --- | --- |
| "Simplest version: just stub this / return a placeholder" | A stub is an *unsolved* task, not a simpler solution. |
| "I'll keep it minimal and leave a TODO" | YAGNI defers *unneeded* features, never *needed* behaviour. |
| "Shortest diff wins, so I'll touch the smallest spot" | Smallest diff in the wrong place is a second bug. |
| "Skipped the error/edge handling to stay lean" | Correctness is never the thing you minimise. |
| "Simple enough to be obviously right — didn't run it" | Unverified is not done. Run it. |
| "Deleted that code, it looked unused" | Removing needed behaviour to shrink the diff is under-delivery. |

## Hard stops

- **Minimal ≠ incomplete.** If it doesn't solve the task and run, it isn't done — "smaller" is only a tiebreaker between two solutions that *both fully work*.
- Before claiming done: it runs / passes its check; it handles the inputs the task implies; no TODO or placeholder sits on a path the task needs *now*. A stub on a required path is an automatic fail (confirm with `verifying-completion`).
- **Never minimise away:** input validation at a trust boundary, error handling that prevents data loss, security, accessibility, or anything the user explicitly asked for.

## Minimal vs unfinished

Before shipping, put every cut on the right list. **Minimal:** fewer abstractions, files, dependencies, lines — for the *same working behaviour*. **Unfinished:** missing behaviour, stubs, unhandled cases, untested logic, deleted-but-needed code. Cutting from the first list is the skill; cutting from the second is the failure this skill exists to stop.

## The one exception

A throwaway spike answering a single question, or pure config/content with no logic — there's no task-correctness to protect, so minimise freely. Everything with real behaviour gets the full discipline.

For the ladder in depth, worked minimal-vs-bloated examples, and the full carve-out list, see `references/yagni-in-depth.md`.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [NjoyimPeguy](https://github.com/NjoyimPeguy)
- **Source:** [NjoyimPeguy/augments](https://github.com/NjoyimPeguy/augments)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-njoyimpeguy-augments-yagni
- Seller: https://agentstack.voostack.com/s/njoyimpeguy
- Browse the marketplace: https://agentstack.voostack.com/browse

---
Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.