Open-Source Observability · Seldaek

monolog

Monolog is a mature, widely-adopted PHP logging library that routes logs to files, databases, email, and web services. It implements the PSR-3 standard interface, making it interoperable with other PHP frameworks and applications.

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Source: GitHub — github.com/Seldaek/monolog

21.4k

GitHub stars

1.9k

Forks

PHP

Primary language

MIT

License (OSI-approved)

Key facts

Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.

Field	Value
Repository	Seldaek/monolog
Owner	Seldaek
Primary language	PHP
License	MIT — OSI-approved
Stars	21.4k
Forks	1.9k
Open issues	26
Latest release	3.10.0 (2026-01-02)
Last updated	2026-07-02
Source	https://github.com/Seldaek/monolog

What monolog is

Monolog provides a handler-based architecture for flexible log routing, supports structured logging via PSR-3 LoggerInterface, and offers formatters and processors for log manipulation. Current version (3.x) requires PHP 8.1+, with legacy branches supporting older versions.

Quickstart

Get the monolog source

Clone the repository and explore it locally.

terminalbash

1git clone https://github.com/Seldaek/monolog.git2cd monolog3# follow the project's README for install & configuration

Need it deployed, integrated, or customized instead? DEV.co ships production installs.

Best use cases

Multi-destination log aggregation

Route logs simultaneously to files, syslog, email, Slack, or centralized services (e.g., Better Stack) using composable handler stack without application code changes.

Framework-integrated logging

Leverage native integration in Symfony, Laravel, Drupal, Magento, and other major PHP frameworks to standardize logging across microservices and monolithic applications.

Structured and contextual logging

Embed request IDs, user context, and custom metadata into logs via processors and formatters, enabling better observability and debugging in distributed systems.

Implementation considerations

Handler selection and chaining directly impacts log destination; design handler stack early based on required outputs (file, email, external service).
PSR-3 interface adoption ensures compatibility with other libraries; code to the interface, not Monolog directly, for future logger swappability.
Log levels and formatting must align with downstream consumers (e.g., JSON for aggregation platforms, plain text for human review); use appropriate formatters.
Processor registration order matters; custom processors should be added in sequence that reflects intended enrichment flow (e.g., request ID, then user context).
Error handling for remote handlers (e.g., network failures to logging service) requires review—determine graceful degradation vs. circuit breaker patterns.

When to avoid it — and what to weigh

PHP < 8.1 required — Monolog 3.x requires PHP 8.1+. Older codebases locked to PHP 7.2–8.0 must use legacy v2.x or v1.x branches, which have limited maintenance.
Non-PSR-3 logging contracts — Applications with custom or non-standard logger interfaces may require adapter code or refactoring to benefit from Monolog's ecosystem and handlers.
Extremely high-throughput, low-latency requirements — No performance benchmarks provided. If sub-millisecond latency or millions-of-logs-per-second throughput is critical, load testing is required before commitment.
Strict runtime dependency minimization — Monolog's handler ecosystem requires additional optional dependencies (curl, mail functions, database drivers). Bare-minimum installations may still be possible but require careful composition.

License & commercial use

Licensed under MIT License. Permissive OSI-approved license permitting commercial use, modification, and distribution with minimal restrictions. Requires retention of license notice and copyright attribution.

MIT is a permissive open-source license that explicitly allows commercial use, proprietary applications, and closed-source derivative works. No commercial support guarantee is built into the license; commercial support is available via Tidelift subscription and GitHub sponsorship, which are optional.

DEV.co evaluation signals

Editorial assessment — not user reviews. Directional, with an explicit confidence level.

Signal	Assessment
Maintenance	Active
Documentation	Adequate
License clarity	Clear
Deployment complexity	Low
DEV.co fit	Strong
Assessment confidence	High

Security considerations

Handlers sending logs to remote services (email, HTTP endpoints, databases) should validate TLS/HTTPS configurations and credentials. Sensitive data (passwords, tokens) in log context may be exposed to downstream services; implement filtering via processors or handlers. No known vulnerabilities disclosed in provided data; security patches depend on community vigilance and maintainer responsiveness. Review third-party handlers for injection risks and authentication weaknesses.

Alternatives to consider

PHP-PSR/Log (psr/log)

Bare PSR-3 interface only; no handlers or formatters. Use if you prefer minimal dependencies and implement custom handler logic, or integrate with lightweight logging systems.

Serilog (C#-inspired, available via some PHP ports)

Alternative structured logging approach; some PHP libraries (e.g., Monolog-like alternatives in Go or Node) offer more modern API patterns, though ecosystem adoption is lower in PHP.

Custom logger implementation

If PSR-3 compliance is only requirement and your application has minimal handler needs, a lightweight in-house logger may reduce dependencies, though sacrifices community handlers and maintenance burden.

Software development agency

Build on monolog with DEV.co software developers

Our engineering team can design robust logging strategies, implement handlers for your stack, and optimize for production scale. Contact us for a technical consultation.

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Related open-source tools

Surfaced by semantic similarity across the DEV.co open-source index.

monolog-bundle zerolog NLog

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monolog FAQ

Does Monolog work with my PHP version?

Monolog 3.x requires PHP 8.1 or above. For PHP 7.2–8.0, use Monolog 2.x. PHP 5.3–8.1 is supported by Monolog 1.x, but maintenance is limited. Check your project's PHP version before upgrading.

Can I send logs to multiple destinations simultaneously?

Yes. Monolog's handler stack allows multiple handlers in one logger instance. Push handlers for file, syslog, email, HTTP endpoints, etc., and all logs route to all handlers (filtered by log level if configured).

Is there a performance impact for high-volume logging?

Not quantified in provided data. For critical throughput requirements (millions of logs/sec), conduct load testing with your handler configuration. Asynchronous or buffered handlers may mitigate latency.

Do I need to pay for Monolog?

Monolog itself is free (MIT License). Optional commercial support and maintenance are available through Tidelift subscription or GitHub sponsorship, not required for use.

Software developers & web developers for hire

DEV.co is a software development agency delivering custom software development services to companies building on open source. Our software developers and web developers design, integrate, and ship production systems — spanning web development, APIs, AI, data, and cloud. If monolog is part of your open-source observability roadmap, our team can implement, customize, migrate, and maintain it.

Need Monolog integration or logging architecture review?

Our engineering team can design robust logging strategies, implement handlers for your stack, and optimize for production scale. Contact us for a technical consultation.

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