typescript-patterns

typescript-patterns is a cursor rule for Codex from prisma/prisma-next. It costs 0 tokens per session (308 once invoked), scanned A, original, Apache-2.0.

A short set of TypeScript and software-architecture rules covering type narrowing, interfaces, factory functions, generic parameters, and test-only type escapes.

In plain words
What is it for?
It guides the design of typed APIs, object construction, generic types, and safe exceptions in tests.
Why use it?
It gives developers consistent patterns for keeping types checked and implementation details contained in this codebase.

Cursor rule for Codex

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/prisma/prisma-next/typescript-patterns
Clone the repo
git clone --depth 1 https://github.com/prisma/prisma-next

Made for: Codex.

Wrote 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.

agentmods badge for typescript-patterns

README.md
[![agentmods](https://agentmods.dev/badge/rules/prisma/prisma-next/typescript-patterns.svg)](https://agentmods.dev/rules/prisma/prisma-next/typescript-patterns)
Your own site
<a href="https://agentmods.dev/rules/prisma/prisma-next/typescript-patterns"><img src="https://agentmods.dev/badge/rules/prisma/prisma-next/typescript-patterns.svg" alt="Measured on agentmods" height="20"></a>
Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 308 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.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00308
Opus 5 $0.00000 $0.00154
Sonnet 5 $0.00000 $0.00062
Haiku 4.5 $0.00000 $0.00031

Measured yesterday against content hash 4ece26c1b621, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

typescript-patterns 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.

.agents/rules/typescript-patterns.mdc · 30 lines

What it actually says

TypeScript and Architecture Patterns

This rulecard is intentionally short. For deeper examples, see docs/reference/typescript-patterns.md.

Focused rulecards

  • .cursor/rules/generic-parameters.mdc — Generic parameter defaults
  • .cursor/rules/interface-factory-pattern.mdc — Interface-based design + factory functions
  • .cursor/rules/type-predicates.mdc — Replace blind casts with type predicates
  • .cursor/rules/test-mocking-patterns.mdc — Type assertions and mocking patterns in tests

Quick reminders

  • No blind casts in production: as unknown as X is forbidden outside tests. Prefer type predicates or fix the type surface.
  • Export interfaces; construct via factories: keep classes as private implementation details.
  • No generic defaults unless meaningful: defaults are semantics, not “flexibility”.
  • Test-only escapes: @ts-expect-error and double casts are acceptable only in test files, with a short explanation.
  • .cursor/rules/no-inline-imports.mdc
  • .cursor/rules/object-hasown.mdc
  • .cursor/rules/prefer-assertions-over-defensive-checks.mdc
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 · 30 lines · 0 tokens per session scan A 4ece26c1b621

Subscribe to this mod's changes

typescript-patterns is a cursor rule published in the GitHub repository prisma/prisma-next (419 stars, last pushed 10d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 308 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 2026-09-03.