Set the Node.js, Python, Go or Ruby version

Lizard reads the runtime version from files in your project when lizardpack builds it: .nvmrc or engines.node for Node.js, .python-version or requires-python for Python, the go line of go.mod for Go, and .ruby-version or the Gemfile ruby line for Ruby. To change the version, edit that file and deploy again. Without one, Lizard uses Node.js 22, Python 3.13, Go 1.24 or Ruby 3.4.

Test status: we checked every rule on this page on 2026-10-12 by running lizardpack, the build planner Lizard’s builders run, against sample projects.

Where Lizard looks

Lizard uses the official image tag for the major or major/minor version and drops the patch number. Each build gets the patch release that tag points to when the build runs.

These files apply only when lizardpack writes the Dockerfile. See when Lizard ignores version files.

Change the Node.js version

echo 24 > .nvmrc
lizard up --service web

With a GitHub service, commit the file and push instead. Rules:

• Write a number: 24, v24 and 24.1.0 all select Node.js 24. Lizard skips lines that start with #.
• Lizard skips lts/* and node in .nvmrc and moves on to the next file. It uses other aliases, such as lts/iron, as written, and the build fails.
• .nvmrc wins over engines.node.
• engines.node gives the lowest version in its range: >=18 builds on Node.js 18, and ^20.11.0 on Node.js 20. A range with ||, such as 18 || 20, fails the build.

Change the Python version

echo 3.12 > .python-version
lizard up --service web

• .python-version must hold a version number such as 3.12 or 3.12.4. Lizard skips lines that start with #. It also skips other values, such as pypy3.10, and moves on to the next file.
• requires-python = ">=3.11" builds on Python 3.11, the lowest version in the range.
• A range with an upper bound, such as ">=3.11,<3.14", produces an image name that does not exist and the build fails. Add a .python-version file; it wins.
• runtime.txt is not read.

Change the Go version

go mod edit -go=1.25
lizard up --service api

Lizard reads only the go line. It does not read the toolchain line.

Change the Ruby version

echo 3.4.1 > .ruby-version
lizard up --service web

Write the bare number. rails new writes ruby-3.4.1, and Lizard does not strip the ruby- prefix, so the build fails. A Gemfile line such as ruby "~> 3.3.0" builds on Ruby 3.3. A Rails app that keeps its generated Dockerfile takes the version from that file instead; see Deploy a Rails app.

When Lizard ignores version files

• Your own Dockerfile. Its FROM line decides, for example FROM node:24-slim. See Deploy a Docker container from a Dockerfile.
• A build or start command on the service. Lizard then writes a Dockerfile from the commands on a fixed image: node:22-alpine, python:3.13-slim or golang:1.24-alpine, chosen by the first word of the command. To return to version files, clear both:

lizard service set web --set buildCommand= --set startCommand=

Clearing buildCommand on a running service starts a rebuild by itself. Check lizard events before you run lizard redeploy, so you do not queue a second build. See the build decision order.

Check which version a build used

lizard logs --build --service web

The build log names the base image, such as node:24-slim or python:3.12-slim. To check the version at run time, print it when your app starts, for example process.version in Node.js or sys.version in Python, and read lizard logs --service web.

Related

• Build pipeline
• Deploy a Node.js app
• Deploy a Go app
• Deploy a Streamlit app
• Deploy FastAPI
• Deploy Django

Updated October 12, 2026