mtail

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What mtail is

mtail is free, self-hosted software that turns application log lines into metrics for monitoring. It connects applications whose internal state appears only in logs to alerting and dashboard systems without changing those applications for instrumentation. Users write mtail programs defining patterns and actions for processing lines. Extracted metrics can be scraped over HTTP as JSON or Prometheus data, or pushed periodically to collectd, StatsD, or Graphite. mtail supports Linux, macOS, Windows, and Docker deployments, including a sidecar reading logs from a shared volume. A deployment can run one instance per machine while monitoring multiple applications. The project is intended for real-time or near-real-time monitoring, not log archiving, indexing, searching, or data-mining. It is stateless, so variables and metric values do not survive restarts. It also leaves complex mathematical processing to time-series systems.

Who it suits

mtail suits teams that need to derive monitoring metrics from existing application logs without adding instrumentation to those applications. It is intended for self-hosted deployments on supported operating systems or Docker.

What it does well

Free Apache-2.0 open-source software
Extracts metrics from application logs
Supports JSON and Prometheus scraping
Runs on Linux, macOS, Windows, and Docker
Can monitor multiple applications per machine

What to know first

No SSL or HTTP authentication
No transport security for logs
Metric values do not persist across restarts
Not designed for log search or data mining

Plans

Plan	Billed and limits	Price
mtail	Open-source software under the Apache-2.0 license	Free

As google.github.io lists them, read 11 Oct 2026. The maker's own page has the final word.

Verdict

mtail provides a focused path from log output to monitoring metrics, with several export options and flexible deployment. Separate security and long-term storage systems are required, and it does not replace a searchable log archive.

Facts from mtail's own pages

Archive export: No · google.github.io, 21 Sept 2026
Containers: The project can be run with Docker, including as a sidecar that reads an application container’s logs exposed through a volume. · google.github.io, 11 Oct 2026
Deployment: The deployment guide describes running one mtail instance per machine to monitor multiple applications on that machine. · google.github.io, 11 Oct 2026
Export formats: Metrics can be scraped over HTTP as JSON or Prometheus format, or pushed periodically to collectd, StatsD, or Graphite. · google.github.io, 11 Oct 2026
Free plan: Yes · google.github.io, 21 Sept 2026
Live log tailing: Yes · google.github.io, 21 Sept 2026
Log analysis limit: mtail is intended for real-time or near-real-time monitoring and does not copy, index, or search logs for data-mining applications. · google.github.io, 11 Oct 2026
Log pipelines: No · google.github.io, 21 Sept 2026
Metric processing limit: The programming guide says mtail deliberately does not implement complex mathematical functions and leaves that work to time-series systems such as Prometheus. · google.github.io, 11 Oct 2026
Metric programs: Extraction is controlled by mtail programs that define patterns and actions for processing log lines. · google.github.io, 11 Oct 2026
Platforms: The project README says precompiled binaries are available for Windows, OSX, and Linux. · github.com, 11 Oct 2026
Purpose: mtail extracts metrics from application logs so they can be exported to a time-series database or calculator for alerting and dashboards. · google.github.io, 11 Oct 2026
Security: The interoperability guide says mtail does not support SSL or HTTP authentication and recommends using a VPN tunnel or reverse proxy to protect access. · google.github.io, 11 Oct 2026
State persistence: mtail is intended to be stateless and does not persist variables or metric values between restarts, deferring long-term storage to a time-series database and collector. · google.github.io, 11 Oct 2026
Structured log parsing: Yes · google.github.io, 21 Sept 2026
Support: The project README directs questions to GitHub Discussions and a users mailing list, and directs defect reports to GitHub Issues. · github.com, 11 Oct 2026
Transport security: The guide says mtail does not provide transport security for logs and recommends using a proper syslog tool to transmit and receive logs over a network. · google.github.io, 11 Oct 2026
Use case: It connects applications that expose internal state only through logs to monitoring systems, without requiring those applications to be patched for instrumentation. · google.github.io, 11 Oct 2026

Where mtail stands on Freedom251

Log Management Software#40 of 111