02-api

Rules for building an Express.js API, a web server that receives requests and returns data, with separate layers for requests, business logic, and database access.

In plain words
What is it for?
Use them when adding or changing versioned REST endpoints, services, database entities, migrations, API clients, or React Query data hooks.
Why use it?
They keep validation, data conversion, errors, routes, and database queries in predictable places.

Cursor rule

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/wellapp-ai/well/02-api
Clone the repo
git clone --depth 1 https://github.com/WellApp-ai/Well
Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 265 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 $0.00265
Opus 5 $0.00000 $0.00133
Sonnet 5 $0.00000 $0.00053
Haiku 4.5 $0.00000 $0.00026

Measured 2d ago against content hash 0fcc73ca8fda, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

02-api 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/rules/02-api.mdc · 37 lines

What it actually says

API Rules (Express.js)

Service Pattern

  • Business logic lives in /lib/services/
  • Controllers handle HTTP concerns only
  • Services handle data transformation and validation

3-Layer Architecture

  1. ApiClient (/lib/api/client.ts): HTTP, auth, error handling
  2. Service Layer (/lib/services/): Business logic, type mapping
  3. Query Hooks (/lib/queries/): React Query integration

Database

  • MikroORM for entities and queries
  • Use Context7 MCP for MikroORM patterns
  • Migrations in /hasura/migrations/

Endpoints

  • Version prefix: /v1 (handled by router)
  • RESTful naming conventions
  • JSON:API response format
  • Add endpoint to API_ENDPOINTS in /lib/api/constants.ts

Error Handling

  • Use ApiError class for HTTP errors
  • Log with proper levels (error, warn, info)
  • Never expose internal errors to clients

Query Keys

  • Centralize in /lib/queries/keys.ts
  • React Query config: 5min staleTime, 10min gcTime
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. 2d ago First seen · 37 lines · 0 tokens per session scan A 0fcc73ca8fda

Subscribe to this mod's changes

02-api is a cursor rule published in the GitHub repository WellApp-ai/Well (341 stars, last pushed 25d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 265 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.