log5424

A lightweight RFC 5424 syslog message builder and parser for JavaScript and Node.js.

This library focuses on generating valid, structured syslog messages with practical defaults, strict validation, and a simple API that works well for both one-off logs and reusable logger instances.

Installation

npm install log5424

Quick Start

import { debug } from "log5424";

const line = debug("service started");

console.log(line);
// <135>1 2026-04-08T12:00:00.000Z my-host worker 1234 - - service started

See the full API at https://travishorn.github.io/log5424/.

Usage Patterns

1) Direct severity functions

import { error, info } from "5424";

console.log(info("ready"));
console.log(error("database connection failed", { appName: "api" }));

2) Reusable logger with custom options

import { createLogger } from "log5424";

const logger = createLogger({ facility: "local4", appName: "checkout" });

console.log(logger.debug("cache hit"));
console.log(logger.error("payment declined", { msgId: "payment-error" }));
console.log(logger("app started")); // defaults to "debug" or custom severity you set when creating the logger

Structured Data

Structured data can be provided in multiple forms:

• Raw RFC 5424 string
• Single object with sdId
• Array of objects with sdId

import { info } from "log5424";

const line = info("request complete", {
  structuredData: [
    { sdId: "http@32473", method: "GET", path: "/health" },
    { sdId: "trace@32473", requestId: "abc-123" },
  ],
});

Parsing

Use parse() to parse syslog messages.

import { parse } from "log5424";

const parsed = parse(
  "<128>1 2026-01-01T00:00:00.000Z host app 42 event - hello",
);

console.log(parsed.priority); // 128
console.log(parsed.facility); // 16
console.log(parsed.severity); // 0

Validation and Error Behavior

Inputs are validated aggressively and throw descriptive TypeError/Error messages for invalid values.

Examples of validations include:

• Facility range/name correctness
• Severity range/name correctness
• RFC 3339 timestamp validity
• Token whitespace constraints for hostname/appName/msgId
• Structured data shape and formatting

Development

Fork and clone the repository.

Install dependencies:

npm install

Check formatting:

npm run check:format

Check types:

npm run check:types

Lint code:

npm run check:lint

Run tests:

npm test

Ideas for Further Development

• Support for RFC 3164
• Transports (std, file, udp, tcp)
• Relay/collector architecture roles

License

The MIT License

Copyright 2026 Travis Horn

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.