logging-and-observability

Original：🇺🇸 English

Translated

Adds structured JSON logging, correlation/trace IDs, metrics, and health endpoints. Use when wiring observability for a new service, debugging cross-service requests, or removing console.log.

28installs

Sourcej4flmao/agent_skills_nodejs_nestjs

Added on2026-09-12

NPX Install

npx skill4agent add j4flmao/agent_skills_nodejs_nestjs logging-and-observability

SKILL.md Content

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Logging and Observability

When to use

Wiring observability for a new service
Debugging cross-service requests
Removing
```
console.log
```
from production code

Core rules

Structured JSON logs in production, pretty in development
Every log entry has
```
timestamp
```
,
```
level
```
,
```
message
```
,
```
traceId
```
No
```
console.log
```
in production code
Correlation/trace ID passed through async context
Health endpoint (
```
/health
```
) and readiness endpoint (
```
/ready
```
)

Reference shape (TypeScript)

Logger Interface (Port)

typescript

export interface Logger {
  info(message: string, meta?: Record<string, unknown>): void;
  warn(message: string, meta?: Record<string, unknown>): void;
  error(message: string, meta?: Record<string, unknown>): void;
  debug(message: string, meta?: Record<string, unknown>): void;
}

JSON Logger Implementation

typescript

export class JsonLogger implements Logger {
  constructor(private traceId?: string) {}

  info(message: string, meta?: Record<string, unknown>): void {
    this.log('info', message, meta);
  }

  private log(level: string, message: string, meta?: Record<string, unknown>): void {
    const entry = {
      timestamp: new Date().toISOString(),
      level,
      message,
      traceId: this.traceId,
      ...meta,
    };
    console.log(JSON.stringify(entry));
  }
}

Examples — Do

typescript

this.logger.info('User created', { userId: user.id, email: user.email.value });

Examples — Don't

typescript

// ❌ Console.log in production code
console.log('User created:', user);
// ❌ No trace ID
logger.info('Request processed');

Checklist

Structured JSON logger implemented
Trace/correlation ID in every log entry
Health and readiness endpoints created
No
```
console.log
```
in production code

See reference/logging-patterns.md for full patterns.

logging-and-observability

NPX Install

Tags

SKILL.md Content

Logging and Observability

When to use

Core rules

Reference shape (TypeScript)

Logger Interface (Port)

JSON Logger Implementation

Examples — Do

Examples — Don't

Checklist