How to fix failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name in Docker

DockerINTERMEDIATEMEDIUMUpdated Dec 6, 2025· 176 views

The 'failed to parse stage name' error occurs when Docker BuildKit cannot properly parse a stage name in a FROM instruction. This typically happens due to uppercase letters in stage names, undefined ARG variables, or invalid characters. The fix involves using lowercase stage names and ensuring all build arguments are properly defined.

Quick fix

Fixes failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name

# Wrong - uppercase stage names
FROM node:20-alpine AS BUILD
WORKDIR /app
COPY package*.json ./
RUN npm ci

FROM node:20-alpine AS RUNTIME
COPY --from=BUILD /app/node_modules ./node_modules

# Correct - lowercase stage names
FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci

FROM node:20-alpine AS runtime
COPY --from=build /app/node_modules ./node_modules

Convert stage names to lowercase
Declare ARG before the first FROM
Pass build arguments correctly
Fix empty or invalid variable values

docker — error

$# Wrong - uppercase stage names
FROM node:20-alpine AS BUILD
WORKDIR /app
COPY package*.json ./
RUN npm ci
FROM node:20-alpine AS RUNTIME
COPY --from=BUILD /app/node_modules ./node_modules
# Correct - lowercase stage names
FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci
FROM node:20-alpine AS runtime
COPY --from=build /app/node_modules ./node_modules
failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name

What this error means

This error indicates that Docker's build system (BuildKit) encountered a stage name it couldn't parse in your Dockerfile. The error typically appears during `docker build` operations when using multi-stage builds or ARG variables in FROM instructions. The full error message usually looks like: ``` failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name "STAGENAME": invalid reference format ``` This happens because Docker's image reference parser has strict rules about what constitutes a valid name. When a stage name violates these rules - whether due to uppercase letters, missing variable values, or invalid characters - the build fails immediately before any actual building occurs. The error originates from BuildKit's LLB (Low-Level Builder) definition phase, which parses the entire Dockerfile and constructs a build graph before executing any instructions.

Typical symptoms

docker build fails immediately without building any layers
Error message mentions 'failed to parse stage name' with the problematic name shown
The error includes 'invalid reference format' or 'repository name must be lowercase'
Multi-stage builds that previously worked now fail after upgrading Docker
CI/CD pipelines fail at the Docker build step with this error
docker-compose build fails when using multi-stage Dockerfiles
The error occurs even though the Dockerfile syntax appears correct

Common causes

Stage name contains uppercase letters (e.g., FROM alpine AS BUILD instead of FROM alpine AS build)
ARG variable used in FROM instruction is undefined or empty (e.g., FROM node:${VERSION} where VERSION is not set)
Stage name starts with a number or contains invalid characters like symbols
Missing ARG declaration before the first FROM statement when using variables
Docker Compose v2 handling ARG variables differently than v1
Image tag contains two colons (e.g., image:tag:latest)
Environment variable not being passed correctly during build
Windows/Linux line ending issues (CRLF vs LF) corrupting the Dockerfile

How to fix "failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name"

1Convert stage names to lowercase

The most common cause is using uppercase letters in stage names. BuildKit requires lowercase stage names:

dockerfile

# Wrong - uppercase stage names
FROM node:20-alpine AS BUILD
WORKDIR /app
COPY package*.json ./
RUN npm ci

FROM node:20-alpine AS RUNTIME
COPY --from=BUILD /app/node_modules ./node_modules

# Correct - lowercase stage names
FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci

FROM node:20-alpine AS runtime
COPY --from=build /app/node_modules ./node_modules

This is especially important when referencing stages with COPY --from= or FROM instructions.

2Declare ARG before the first FROM

When using variables in FROM instructions, the ARG must be declared before the first FROM statement:

dockerfile

# Wrong - ARG after FROM
FROM node:${NODE_VERSION}-alpine
ARG NODE_VERSION=20

# Correct - ARG before FROM
ARG NODE_VERSION=20
FROM node:${NODE_VERSION}-alpine

If you need the variable available in build stages, redeclare it after FROM (ARG values don't persist across stages):

dockerfile

ARG NODE_VERSION=20
FROM node:${NODE_VERSION}-alpine AS build
ARG NODE_VERSION  # Re-declare to use in this stage
RUN echo "Building with Node ${NODE_VERSION}"

3Pass build arguments correctly

Ensure build arguments are passed to the docker build command:

bash

# Check if the ARG has a default value
# If not, you must pass it at build time

# Wrong - missing required argument
docker build -t myapp .

# Correct - passing the argument
docker build --build-arg NODE_VERSION=20 -t myapp .

# Or set a default in Dockerfile
ARG NODE_VERSION=20  # Default value if not provided
FROM node:${NODE_VERSION}-alpine

In docker-compose.yml:

yaml

services:
  app:
    build:
      context: .
      args:
        NODE_VERSION: "20"

4Fix empty or invalid variable values

An empty ARG results in an invalid image reference like node::

bash

# Debug: Check what value is being used
docker build --build-arg NODE_VERSION=20 -t myapp . --progress=plain

# In CI, verify environment variables are set
echo "NODE_VERSION=${NODE_VERSION}"

Common issues in CI/CD:

yaml

# GitHub Actions - variable might be empty
- name: Build
  run: |
    # Verify the variable exists
    if [ -z "${{ env.VERSION }}" ]; then
      echo "VERSION is not set!"
      exit 1
    fi
    docker build --build-arg VERSION=${{ env.VERSION }} -t app .

5Use valid stage name characters

Stage names must follow specific rules:

- Start with a lowercase letter
- Contain only lowercase letters, digits, and separators (., -, _)
- Not contain uppercase letters or special symbols

dockerfile

# Invalid stage names
FROM alpine AS 1stStage      # Cannot start with number
FROM alpine AS my-Stage      # Contains uppercase
FROM alpine AS my@stage      # Contains invalid symbol
FROM alpine AS MY_BUILD      # All uppercase

# Valid stage names
FROM alpine AS stage1
FROM alpine AS my-stage
FROM alpine AS my_stage
FROM alpine AS build.dev
FROM alpine AS base

6Remove duplicate colons in image references

Image references can only have one colon. A common mistake is adding :latest to an already-tagged image:

dockerfile

# Wrong - two colons
FROM node:20-alpine:latest

# Correct - single colon
FROM node:20-alpine
# or
FROM node:latest

This can happen when concatenating variables:

dockerfile

# Wrong - if TAG already contains a colon
ARG TAG=20-alpine
FROM node:${TAG}:latest  # Results in node:20-alpine:latest

# Correct
ARG TAG=20-alpine
FROM node:${TAG}

7Fix line ending issues (CRLF to LF)

Windows line endings (CRLF) can cause parsing issues:

bash

# Check for Windows line endings
file Dockerfile
# If it shows "with CRLF line terminators", convert it:

# Using sed
sed -i 's/\r$//' Dockerfile

# Using dos2unix
dos2unix Dockerfile

# In VS Code: Click "CRLF" in status bar and select "LF"

In Git, configure automatic conversion:

bash

# .gitattributes
Dockerfile text eol=lf
*.sh text eol=lf

8Handle Docker Compose v1 to v2 migration

Docker Compose v2 may handle ARG values differently:

yaml

# docker-compose.yml
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        # Explicitly set all ARGs
        NODE_VERSION: "20"
        # Or reference environment variables
        BUILD_ENV: ${BUILD_ENV:-production}

If using environment files:

bash

# .env file
NODE_VERSION=20

# Verify variables are loaded
docker compose config

Note: docker-compose (v1) and docker compose (v2) may behave differently. Try both if one fails.

Advanced notes

### Understanding BuildKit and LLB

Docker BuildKit uses LLB (Low-Level Builder) as an intermediate representation. When you run docker build, BuildKit:

1. Parses the Dockerfile into an LLB definition
2. Validates all references (including stage names)
3. Constructs a dependency graph
4. Executes the build

The "failed to parse stage name" error occurs at step 2, before any actual building. This is why the error appears immediately without any layer building.

### BuildKit vs Legacy Builder

The legacy builder (pre-BuildKit) was more lenient with stage names. When Docker Desktop or newer Docker versions default to BuildKit, previously working Dockerfiles may fail:

bash

# Temporarily disable BuildKit (not recommended for production)
DOCKER_BUILDKIT=0 docker build -t myapp .

# Check current BuildKit status
docker buildx version

However, rather than disabling BuildKit, fix the Dockerfile to comply with its stricter requirements.

### Multi-stage Build Best Practices

dockerfile

# Use descriptive lowercase stage names
ARG GO_VERSION=1.21

FROM golang:${GO_VERSION}-alpine AS deps
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download

FROM deps AS build
COPY . .
RUN go build -o /app/server .

FROM alpine:3.18 AS runtime
COPY --from=build /app/server /usr/local/bin/
ENTRYPOINT ["server"]

### Debugging Stage Name Issues

bash

# Parse Dockerfile without building
docker buildx build --print .

# Build with verbose output
docker build --progress=plain -t myapp .

# Check what variables are being used
docker build --build-arg NODE_VERSION=20 -t myapp . 2>&1 | head -20

### CI/CD Considerations

In CI environments, ensure ARG values are explicitly passed:

yaml

# GitHub Actions
- name: Build Docker image
  run: |
    docker build \
      --build-arg NODE_VERSION=${{ matrix.node-version }} \
      --build-arg BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ') \
      -t myapp:${{ github.sha }} \
      .

# GitLab CI
build:
  script:
    - docker build
        --build-arg CI_COMMIT_SHA=$CI_COMMIT_SHA
        --build-arg NODE_VERSION=${NODE_VERSION:-20}
        -t $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG .

Frequently asked questions

What does "failed to solve with frontend dockerfile.v0: failed to build LLB: fail" mean?: This error indicates that Docker's build system (BuildKit) encountered a stage name it couldn't parse in your Dockerfile. The error typically appears during docker build operations when using multi-stage builds or ARG variables in FROM instructions. The full error message usually looks like: This happens because Docker's image reference parser has strict rules about what constitutes a valid name.
How do I fix "failed to solve with frontend dockerfile.v0: failed to build LLB: fail"?: The 'failed to parse stage name' error occurs when Docker BuildKit cannot properly parse a stage name in a FROM instruction. This typically happens due to uppercase letters in stage names, undefined ARG variables, or invalid characters. The fix involves using lowercase stage names and ensuring all build arguments are properly defined.
What causes "failed to solve with frontend dockerfile.v0: failed to build LLB: fail"?: Stage name contains uppercase letters (e.g., FROM alpine AS BUILD instead of FROM alpine AS build) ARG variable used in FROM instruction is undefined or empty (e.g., FROM node:${VERSION} where VERSION is not set) Stage name starts with a number or contains invalid characters like symbols
Is the "failed to solve with frontend dockerfile.v0: failed to build LLB: fail" error serious?: It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

Official resources & further reading

📚Docker Official Documentation
💬
Stack Overflow - Failed to parse stage name postgres(Stack Overflow)
🐙
GitHub - Cannot FROM a previous stage whose name contains uppercase letters(GitHub)
🐙
GitHub - Lowercase error when using automatic platform args in stage names(GitHub)
💬
Docker Forums - Failed to solve: failed to parse stage name(Stack Overflow)
📖
Docker Docs - Multi-stage builds(Official Docs)
📝
100 Common Docker Errors & Solutions

How to fix failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name in Docker

Quick fix

What this error means

Typical symptoms

Common causes

How to fix "failed to solve with frontend dockerfile.v0: failed to build LLB: failed to parse stage name"

Advanced notes

Frequently asked questions

Related errors

Official resources & further reading