typescript-best-practices

A set of best practices for TypeScript, a programming language that adds type checking to JavaScript. It focuses on modeling data safely and avoiding unchecked values or casts.

In plain words
What is it for?
For reading or editing TypeScript and TSX files, especially when defining data variants, validating external input, and handling arrays or ranges safely.
Why use it?
It reduces bugs caused by ambiguous data shapes, unsafe assumptions, and turning off the type checker.

Skill for Claude CodeCodex

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 skills/painhardcore/pstack/typescript-best-practices
Any agent
npx skills add painhardcore/pstack --skill typescript-best-practices
Clone the repo
git clone --depth 1 https://github.com/painhardcore/pstack

Made for: Claude Code, Codex.

Per session 24 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 615 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 92% copy Near-identical to another mod 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 $0.00024 $0.00615
Opus 5 $0.00012 $0.00308
Sonnet 5 $0.00005 $0.00123
Haiku 4.5 $0.00002 $0.00061

Measured yesterday against content hash df0ecd7518b3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

typescript-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 yesterday.

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.

Origin

This is a copy

92% identical to typescript-best-practices — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.opencode/skills/typescript-best-practices/SKILL.md · 29 lines

What it actually says

TypeScript best practices

Apply the type-system-discipline principle skill first; this skill grounds it in TypeScript syntax.

Rule Summary
Discriminated unions Model variants with a kind literal discriminant so impossible states can't be represented. No optional-field bags.
Branded types Brand primitives with & { readonly __brand: "X" } so they can't be mixed up. Validate once at creation.
Constructive modeling Build the shape so the illegal value can't be constructed. [T, ...T[]] for non-empty, [T, T][] for even length, start plus duration for a range. Not a runtime guard, not a wish for refinement types.
Simplest total type Keep T[] while every operation on it stays total. Strengthen to NonEmpty<T> only where the loose type forces !, a cast, or a "should never happen" throw.
unknown over any External data is unknown. any disables type checking everywhere it touches.
No as casts Every as is a runtime crash waiting. Cast only after validation.
Narrowing hierarchy Discriminant switch > in operator > typeof/instanceof > user-defined type guard > as.
Type guards Must verify the claim. A lying guard is worse than as because the bug hides behind a name that says it's safe. Name them isX or hasX.
Exhaustiveness Inline const _exhaustive: never = x; in default arms so the compiler errors when a new variant is added.
satisfies over as Validates the value without widening literal types.
Boundary validation Parse where data crosses in, into a named domain type. Record<string, unknown> (however spelled) stops at that parse. Trust types inside. See the boundary-discipline principle skill.
Schema-derived types Reach for Pick/Omit/Parameters/ReturnType/Awaited/typeof before declaring a new interface.
Object args Pass objects, not positional, so argument order is self-documenting. Skip on hot paths (per-frame render, tokenizers, parsers).
Real tests Don't mock what you can run. Prefer the framework's real test primitives with leak/disposable checks, and verify UI in a running build. Mock only what you can't run locally.
Structured telemetry Prefer structured logger diagnostics with enough context to debug from an id. No console.log in shipped code.

Examples: references/patterns.md.

Files

What ships with it

1 file 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.

  1. yesterday First seen · 29 lines · 24 tokens per session scan A df0ecd7518b3

Subscribe to this mod's changes

typescript-best-practices is a skill published in the GitHub repository painhardcore/pstack (1 stars, last pushed 5d ago), licensed MIT. It adds 24 tokens to every session and 615 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. It is 92% identical to typescript-best-practices, differing in 2 lines, and is treated as a copy.

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