A set of rules for writing safer TypeScript code, including checking unknown values, handling missing data, and using reusable type patterns.

Use it when defining type guards, handling optional fields, setting defaults, or writing generic functions and hooks.

It reduces errors caused by unexpected data, null or undefined values, and unclear types.

typescript — Cursor rule by kubev2v

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 rules/kubev2v/forklift-console-plugin/typescript

Clone the repo

git clone --depth 1 https://github.com/kubev2v/forklift-console-plugin

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.

When invoked 889 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

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	$0.00000	$0.00889
Opus 5	$0.00000	$0.00445
Sonnet 5	$0.00000	$0.00178
Haiku 4.5	$0.00000	$0.00089

Measured 2d ago against content hash ddb719c291b8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

typescript 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 2d 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.

.cursor/rules/typescript.mdc · 153 lines

How it starts

The opening of the file, as written. The whole thing — 153 lines — stays where its author put it; the contents beside it link to each section on GitHub.

TypeScript Guidelines (Supplement)

For core TypeScript conventions (type vs interface, no any, explicit return types, naming), see AGENTS.md. This rule adds advanced patterns.

1. Type Narrowing

Type Guard Functions

const isProvider = (obj: unknown): obj is V1beta1Provider => {
  return (
    typeof obj === 'object' &&
    obj !== null &&
    'kind' in obj &&
    obj.kind === 'Provider'
  );
};

Discriminated Unions

type FetchState<T> =
  | { status: 'loading' }
  | { status: 'error'; error: Error }
  | { status: 'success'; data: T };

2. Null & Undefined Handling

Optional Chaining for Deep Access

const providerName = provider?.metadata?.name;
const planStatus = plan?.status?.conditions?.[0]?.type;
const vmCount = plan?.spec?.vms?.length ?? 0;

Nullish Coalescing for Defaults

const namespace = provider?.metadata?.namespace ?? 'default';
const conditions = migration?.status?.conditions ?? [];

3. Generics

Constrained Generics

const getResourceName = <T extends { metadata?: { name?: string } }>(
  resource: T,
): string => {
  return resource.metadata?.name ?? 'Unknown';
};

Generic Hooks

const useForkliftResource = <T>(config: WatchConfig): [T | undefined, boolean, Error | undefined] => {
  // implementation
};

4. Utility Types

Built-in

type PartialProvider = Partial<V1beta1Provider>;
type ProviderIdentifier = Pick<V1beta1Provider, 'metadata'>;
type PlanWithoutStatus = Omit<V1beta1Plan, 'status'>;
type LabelMap = Record<string, string>;

Custom

type Nullable<T> = T | null;
type Maybe<T> = T | null | undefined;

type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends object ? DeepPartial<T[P]> : T[P];
};

5. Error Handling Types

type APIError = {
  code: number;
  message: string;
  details?: string;
};

type Result<T, E = APIError> =
  | { success: true; data: T }
  | { success: false; error: E };

Read the full file on GitHub · 153 lines

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.

2d ago First seen · 153 lines · 0 tokens per session scan A ddb719c291b8

Subscribe to this mod's changes

typescript is a cursor rule published in the GitHub repository kubev2v/forklift-console-plugin (11 stars, last pushed 2d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 889 tokens. 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.

Languages Writing and docs

typescript