Crates.io: Rust Package Registry - AI-Optimized Reference

CRITICAL CONFIGURATION

Publishing Requirements

• GitHub OAuth mandatory - no anonymous publishing
• Email verification required - check spam folder for verification
• API token mandatory - save securely, no recovery mechanism
• 10MB package size limit - hard limit, commonly exceeded with assets/target directories
• Immutable versioning - published versions permanent forever, no deletion possible

Production-Ready Cargo.toml Fields

[package]
name = "package-name"
version = "0.1.0"
license = "MIT OR Apache-2.0"  # Required field
description = "Brief description"  # Required field
repository = "https://github.com/user/repo"  # Required field
keywords = ["web", "api", "http"]  # Improves discoverability
categories = ["web-programming"]  # Required for categorization
exclude = ["target/", "assets/", "*.png"]  # Prevents size limit failures

FAILURE MODES & SOLUTIONS

Publishing Failures (September 2025)

Error	Root Cause	Solution
"package not found"	Name taken or typo	Check crates.io search first
"email not verified"	Unverified GitHub email	Check spam folder
"forbidden"	Expired/invalid API token	Regenerate token via crates.io
"failed to verify package tarball"	Workspace publishing bug	Use cargo publish -p crate-name
"this crate exists but you don't seem to be an owner"	Name collision	Choose different name
Size limit exceeded	Assets/target directory included	Configure exclude in Cargo.toml

Silent Failures

• Publishing reports success but package not visible - Always verify on website
• docs.rs build failures - No network access, dev-dependencies unavailable
• Path dependencies during publish - All dependencies must be on crates.io first

RESOURCE REQUIREMENTS

Time Investment

• First-time setup: 30-60 minutes (GitHub OAuth, API token, Cargo.toml configuration)
• Per-package publishing: 5-15 minutes (excluding debugging)
• Documentation failures: 1-4 hours debugging (no network access constraints)

Expertise Requirements

• Basic publishing: Beginner (follow checklist)
• Workspace publishing: Intermediate (dependency ordering critical)
• Alternative registries: Advanced (complex authentication setup)
• Registry operation: Expert (infrastructure knowledge required)

COMPARATIVE ANALYSIS

Crates.io vs Alternatives

Aspect	Crates.io	NPM	PyPI	Assessment
Reliability	High	Medium	Medium	Rarely breaks, AWS-hosted
Version Immutability	Permanent	Can unpublish	Can delete	Prevents left-pad scenarios
Security Scanning	Built-in RustSec	npm audit	Community tools	Automatic vulnerability detection
Private Packages	Not supported	Supported	Supported	Major limitation for enterprises
Package Limit	10MB	100MB	Unlimited	Restrictive for asset-heavy packages

Quality Indicators

• 150,000+ packages (vs NPM's 3M+) - Quality over quantity approach
• Automatic docs.rs integration - Every package gets documentation
• Built-in semver enforcement - Prevents version chaos
• RustSec integration - Proactive security scanning

CRITICAL WARNINGS

Production Gotchas

• Cargo.lock ignored during publishing - CI may pass locally but fail in production
• No rollback mechanism - Mistakes are permanent
• Single point of failure - Entire Rust ecosystem depends on crates.io availability
• No private package support - Everything public by default

Hidden Costs

• Alternative registry setup: $500-2000/month for enterprise solutions
• Documentation debugging: 1-4 hours per failed build
• Name collision resolution: Often requires rebranding
• Migration complexity: High switching costs between registries

OPERATIONAL INTELLIGENCE

Publishing Workflow That Actually Works

1. Pre-flight checks:

   cargo publish --dry-run  # Always run first
   cargo doc --no-deps      # Test documentation build
   

2. Size optimization:

   exclude = ["target/", "*.png", "*.jpg", "docs/", ".git*"]
   

3. Verify publishing:

   • Check website manually (silent failures common)
   • Search may take 5-10 minutes to update
   • docs.rs build status separate from publishing

Team Management Reality

• Full permissions only - No read-only access available
• Owner changes permanent - No audit trail
• Trust model - Any owner can add/remove others

Dependency Management Best Practices

• Pin major versions - Prevents surprise breakage
• Use cargo audit - Weekly vulnerability scanning
• Test after updates - Semver compliance imperfect before 1.0
• Monitor yanked versions - Hidden but still usable

DECISION CRITERIA

Use Crates.io When:

• Building public Rust libraries
• Need automatic documentation
• Want ecosystem integration
• Require security scanning
• Building standard CLI tools

Avoid Crates.io When:

• Need private packages (use alternatives)
• Package exceeds 10MB (asset-heavy applications)
• Require package deletion capability
• Need enterprise support/SLAs

Alternative Solutions

• Private registries: JFrog Cargo Registry ($), Kellnr (self-hosted)
• Git dependencies: Direct repository references
• Path dependencies: Workspace-only solutions
• Custom registries: Alexandrie (open source, complex setup)

BREAKING POINTS

System Limitations

• 10MB absolute limit - No exceptions, no compression help
• Public-only model - No private package support
• Immutable design - No version deletion ever
• Single registry - No built-in mirroring/failover

Ecosystem Dependencies

• GitHub OAuth requirement - No alternative authentication
• docs.rs build constraints - Linux x86_64 only, no network access
• AWS infrastructure - Single point of failure for entire ecosystem
• Rust Foundation funding - Financial dependency for free service

This reference provides the technical reality of operating with crates.io, including the painful lessons learned by the Rust community over years of production use.