uv Troubleshooting

Purpose

Master troubleshooting uv issues, from dependency resolution failures to environment setup problems. Quickly diagnose errors and get your project working again.

Quick Start

Get help immediately when uv fails:

# See what's happening
uv sync --verbose

# Clear cache if something seems broken
uv cache clean

# Force fresh resolution
uv lock --upgrade

# Check your Python installation
uv python list

Most issues resolve with verbose output + cache clearing + fresh resolution.

Instructions

Step 1: Understanding uv Error Categories

uv errors fall into these categories:

Resolution Errors (versions don't match)

error: Failed to resolve version for package X
error: Incompatible versions required

Environment Errors (Python not found)

error: Python X.Y not found
error: No python version available

Cache Errors (corrupted data)

error: Cache is corrupted
error: Invalid cache entry

Network Errors (can't reach PyPI)

error: Failed to fetch from PyPI
error: Connection timeout

Lock File Errors (conflicts)

error: Lock file out of sync with pyproject.toml

Step 2: Debugging Dependency Resolution

Problem: "No matching version found"

# Get verbose output to see what's being checked
uv add package-name --verbose

# Error message might say:
# error: No version of package-name found matching >=2.0,<2.5

# Solutions:
# 1. Check available versions
pip index versions package-name

# 2. Loosen version constraint
uv add "package-name>=2.0"      # Remove upper bound

# 3. Check if package was renamed
# Search PyPI website or use:
pip search package-name

Problem: "Incompatible dependencies"

# Show resolution process
uv add --dry-run package-a package-b

# If both can't work together, you'll see:
# error: Incompatible versions required for package-c:
#   package-a requires package-c>=1.0,<2.0
#   package-b requires package-c>=2.0,<3.0

# Solutions:
# 1. Try newer versions that might be compatible
uv add "package-a>=2.0" "package-b>=3.0"

# 2. Use separate dependency groups
uv add --group ml-cpu torch-cpu
uv add --group ml-gpu torch-gpu
# Install one group at a time

# 3. Contact maintainers if genuinely incompatible

Problem: "Source conflicts"

# Check your PyPI sources
cat pyproject.toml | grep -A 5 "\[tool.uv\]"

# If using custom PyPI index:
# Error might occur due to missing packages in custom index

# Solutions:
# 1. Add fallback to PyPI
[tool.uv]
index-url = "https://custom.index.com/simple"
extra-index-urls = ["https://pypi.org/simple"]

# 2. Or specify per-package
uv add --index-url https://custom.index.com requests

Step 3: Handling Version Conflicts

Problem: Lock file out of sync

# Error message:
# error: The lock file uv.lock is out of sync with pyproject.toml

# Solution 1: Regenerate lock file
uv lock

# Solution 2: Force fresh resolution
uv lock --upgrade

# Solution 3: Clear cache and retry
uv cache clean
uv lock

Problem: Pre-release versions causing issues

# If you see error about pre-release being unavailable:
# error: pre-release version not found

# Check what's actually available
uv python list | grep 3.13

# Solution: Pin stable version instead
uv python pin 3.12   # Use stable instead of rc

Problem: Transitive dependency conflict

# When indirect dependencies conflict:
# package-a requires indirect-dep==1.0
# package-b requires indirect-dep==2.0

# Show dependency tree to find issue
uv tree

# Solution: Update one of the direct dependencies
# Find which needs updating with:
uv tree | grep indirect-dep

# Then update the direct package
uv add "package-a>=2.0"  # Might have updated indirect-dep

Step 4: Cache Issues and Recovery

Problem: Cache corruption

# Symptoms:
# - Same operations fail each time
# - Error messages about cache
# - Slow/hanging operations

# Solution 1: Clean specific cache
uv cache clean all                # Clean everything
uv cache clean --all              # Alternative syntax

# Solution 2: Check cache location
uv cache dir
# On macOS: /Users/username/Library/Caches/uv
# On Linux: ~/.cache/uv
# On Windows: %APPDATA%\uv\cache

# Solution 3: Manual cache deletion (if needed)
rm -rf ~/.cache/uv                # Linux/macOS
rmdir %APPDATA%\uv\cache          # Windows

Problem: Cache growing too large

# Check cache size
du -sh ~/.cache/uv
# Or on macOS/Linux with homebrew-installed uv:
du -sh ~/Library/Caches/uv

# Solution: Clean unused cache
uv cache clean all

# Prevention: Set cache limits in pyproject.toml
[tool.uv]
# Limit cache to 2GB (example)
cache-size = "2G"

Step 5: Environment and Python Issues

Problem: "Python X.Y not found"

# Error: Python 3.12 not found in PATH

# Step 1: Check what Python is available
which python
python --version

# Step 2: List uv's Python installations
uv python list

# Step 3: Install needed version
uv python install 3.12

# Step 4: Pin for project if needed
uv python pin 3.12

# Step 5: Verify
uv python list
python --version

Problem: Wrong Python version being used

# Check which Python uv is using
python --version

# Check project pinning
cat .python-version

# Solutions:
# 1. Pin correct version
uv python pin 3.12

# 2. Or remove pin to use system Python
rm .python-version

# 3. Check PATH if system Python is wrong
echo $PATH
# Make sure correct Python directory is first

Problem: Virtual environment is broken

# Symptoms:
# - Python imports fail
# - Packages installed but not found
# - Mysterious import errors

# Solution: Resync with fresh venv
uv sync --reinstall      # Reinstall all packages
# Or:
uv sync --force-reinstall-all  # Force all packages to reinstall

Step 6: Performance Optimization

Problem: Dependency resolution is slow

# Example: `uv sync` takes 5+ minutes

# Solution 1: Use frozen lock file
uv sync --frozen         # Don't resolve, use existing lock

# Solution 2: Build cache
# Run `uv lock` once, then `uv sync` uses it

# Solution 3: Check for large transitive deps
uv tree | wc -l         # Count total dependencies
# If >100, you might have large dependency tree

# Solution 4: Disable network operations
uv sync --offline       # Use only cached packages

Problem: Large lock files

# If uv.lock is very large (>10MB)
wc -l uv.lock

# Solution 1: Trim unnecessary dependencies
uv remove unused-package

# Solution 2: Use extras to split optional deps
# Instead of: uv add package[all]
# Do: uv add package           # Core only
# Then: uv add --group extras package[optional]

# Solution 3: Check for duplicate versions
grep "^name = " uv.lock | sort | uniq -c | sort -rn
# If duplicates, investigate with:
uv tree | grep duplicate-package

Step 7: Platform-Specific Issues

Problem: Windows PATH issues

# After installing uv, command not found

# Solution 1: Restart terminal/PowerShell
# uv installer modifies PATH, needs restart

# Solution 2: Add to PATH manually
# Find where uv installed:
where uv    # Command prompt
Get-Command uv  # PowerShell

# Solution 3: Use full path
c:\Users\username\.cargo\bin\uv --version

Problem: macOS/Linux permissions

# Error: Permission denied
# "Cannot install to /usr/local/bin"

# Solution 1: Use proper installation
curl -LsSf https://astral.sh/uv/install.sh | sh

# Solution 2: Check shell configuration
echo $PATH
# Ensure ~/.cargo/bin is in PATH

# Solution 3: Fix permissions
chmod +x ~/.cargo/bin/uv

Problem: Docker build failures

# Error building Docker image with uv

# Solution: Use official uv Docker image
FROM ghcr.io/astral-sh/uv:latest as base
FROM python:3.12-slim

# Or install uv in existing image
FROM python:3.12-slim
RUN curl -LsSf https://astral.sh/uv/install.sh | sh
ENV PATH="/root/.cargo/bin:$PATH"
COPY . /app
WORKDIR /app
RUN uv sync

Examples

Example 1: Debugging "No Python Found" Error

# Error when running uv sync:
# error: Failed to find python interpreter

# Step 1: Check what's available
uv python list
# Output shows no Python installed

# Step 2: Install Python 3.12
uv python install 3.12

# Step 3: Pin for project
uv python pin 3.12

# Step 4: Verify
uv python list
uv sync

# Result: Project now works

Example 2: Resolving Version Conflicts

# Error when adding two packages:
# uv add package-a package-b
# error: Incompatible versions required for shared-lib

# Step 1: Get details with dry-run
uv add --dry-run package-a package-b
# Shows: package-a needs shared-lib>=1.0,<2.0
#        package-b needs shared-lib>=2.0

# Step 2: Check newer versions
uv add --dry-run "package-a>=2.0" "package-b>=3.0"
# Works! Newer versions are compatible

# Step 3: Add both
uv add "package-a>=2.0" "package-b>=3.0"

# Result: Both packages installed with compatible versions

Example 3: Fixing Cache Corruption

# Symptoms:
# - Operations fail inconsistently
# - Error: "Cannot read cache entry"
# - uv hanging on sync

# Step 1: Identify cache issue
uv sync --verbose
# Shows cache corruption

# Step 2: Clean cache
uv cache clean all

# Step 3: Rebuild
uv lock --upgrade
uv sync

# Result: Everything works again

Example 4: Windows PATH Setup

# After installing uv on Windows
# Error: "uv is not recognized as an internal or external command"

# Step 1: Verify uv is installed
where uv
# Returns: C:\Users\username\.cargo\bin\uv

# Step 2: Check if in PATH
$env:PATH -split ";" | Select-String ".cargo"
# Should show .cargo path

# Step 3: If missing, restart terminal
# Close and reopen PowerShell/Terminal

# Step 4: Verify works
uv --version
# uv 0.1.39

Example 5: Docker Build Optimization

# Original that fails
FROM python:3.12-slim
RUN pip install uv
COPY . /app
WORKDIR /app
RUN uv sync   # Fails: uv not in PATH

# Fixed version
FROM python:3.12-slim
COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
COPY . /app
WORKDIR /app
RUN uv sync

# Result: Docker image builds successfully

Example 6: Troubleshooting Slow Resolution

# Problem: uv sync takes 2 minutes
# Project has 150+ transitive dependencies

# Step 1: Check what's slow
time uv lock --upgrade
# Takes 90 seconds

# Step 2: Use frozen lock after first sync
uv sync --frozen
# Takes 5 seconds (no resolution)

# Step 3: Only update lock when intentional
uv lock --upgrade    # Do this occasionally
uv sync --frozen     # Use this normally

# Result: 18x faster sync for daily development

Requirements

uv installed (install: curl -LsSf https://astral.sh/uv/install.sh | sh)
Python 3.8+ available (for basic operations)
Internet connection (for downloading packages and resolving versions)
Git (optional, for version control and rollback)
Understanding of dependency resolution (recommended)