# docker: invalid reference format (repository name must be lowercase)

**Code:** `invalid reference format` · **Category:** Docker · **Seen on:** Docker

Docker couldn’t parse the image name — uppercase letters, spaces, an empty variable, or a misplaced option.

## Meaning

Image references must be lowercase and look like [registry/]name[:tag|@digest]. A common cause is $(pwd) with spaces breaking a -v argument, so part of a path is read as the image name, or an unset variable leaving “myorg/:1.0”.

## Common causes

- Uppercase letters in the image name
- Space in a path ($(pwd)) splitting arguments
- Empty variable in the tag (image:${TAG})
- Options placed after the image name
- Smart quotes/dashes pasted from a web page

## Quick fix

1. Lowercase the name
2. Quote paths: -v "$(pwd)":/app
3. Check variables are set (echo "$TAG")
4. Put all options before the image name

## Detailed fix by platform

### Docker

1. `docker run --rm -v "$(pwd)":/app -w /app node:20 npm test`

## How to diagnose

1. **Name** — Uppercase or odd characters?
2. **Variables** — echo each one
3. **Order** — Options before the image?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/docker/invalid-reference-format)