rust-crate-discovery

Rust Crate Discovery and Evaluation

Authority: crates.io API, docs.rs, GitHub REST API, RustSec Advisory Database.

This skill owns the discovery + evaluation phase before a crate enters your Cargo.toml. It uses a bundled Python tool (scripts/crate_eval.py) to fetch signals from 4 sources and produce a weighted 0-100 score with a letter grade (A/B/C/D/F), red-flag list, and a recommendation. It does not own post-adoption governance (rust-dependencies), manifest mechanics (rust-cargo-build), or semver (rust-semver).

Capability Boundaries

✅ Strengths

1. Search crates.io by keyword, category, or name — returns ranked candidates
2. Evaluate a single crate in depth: fetch metadata from crates.io + docs.rs + GitHub + RustSec
3. Compare 2+ crates side-by-side with subscore breakdown
4. Score each crate 0-100 across 6 dimensions: adoption (30), maintenance (25), documentation (15), maturity (15), community (10), license (5)
5. Flag red concerns: stale, advisories, no docs, low adoption with churn, single-maintainer bus factor, no source repo, license missing
6. Recommend the best fit, surfacing blocking concerns before the user adopts
7. Output as human-readable report or machine-readable JSON (for agent consumption)

⚠️ Prerequisites

1. Network access (the tool fetches from crates.io, docs.rs, GitHub, RustSec)
2. Python 3.9+ (no external pip packages — stdlib only)

❌ Out of Scope

1. Post-adoption governance (cargo-deny config, license policy, advisory response workflow) → rust-dependencies
2. Cargo.toml field semantics → rust-cargo-build
3. Semver and breaking-change classification → rust-semver
4. Which std type to use instead of a crate → rust-stdlib

Data Privacy

This skill makes outbound HTTP requests to crates.io, docs.rs, GitHub, and RustSec. The User-Agent identifies the tool. No user data is collected or transmitted beyond the crate name in the URL path (which is public registry data). For private/proprietary crate names, prefer manual review.

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The Evaluation Tool — scripts/crate_eval.py

A stdlib-only Python script. Three subcommands:

# Search candidates
python3 scripts/crate_eval.py search "orm"
python3 scripts/crate_eval.py search "http client" --limit 5
python3 scripts/crate_eval.py search "logging" --category "development-tools::debugging"

# Evaluate one crate in depth
python3 scripts/crate_eval.py eval rbatis
python3 scripts/crate_eval.py eval rbatis --json          # machine-readable
python3 scripts/crate_eval.py eval rbatis -v              # show raw signals
python3 scripts/crate_eval.py eval rbatis --skip-github   # faster, less signal

# Compare multiple candidates
python3 scripts/crate_eval.py compare rbatis diesel sea-orm sqlx

Workflow

1. Search — search "<domain keyword>" to surface candidates. Inspect the top 5-10 by downloads and recency.
2. Shortlist — pick 2-4 names with non-trivial adoption (≥1k downloads) and recent activity.
3. Compare — compare <names...> to get the side-by-side scorecard.
4. Investigate red flags — for the top pick, read the red-flag list. Block on security advisories; investigate stale or single-maintainer concerns.
5. Verify fit — the score measures health, not fitness. Read the crate's docs, check its API shape (rust-api-design lens), confirm it covers your use case.
6. Hand off — once adopted, set up cargo-deny (rust-dependencies) and pin version policy (rust-semver).

Reading the output

=== rbatis === A (92/100) — RECOMMENDED — strong fit, low risk
  version 4.9.6  |  657,356 downloads (19,938 recent)  |  license: Apache-2.0
  Subscores:
    adoption        █████████████░░░░░░░░░░░░  27/30
    maintenance     ████████████░░░░░░░░░░░░░  25/25
    ...
  Red flags:
    ! license not declared

• Grade + score — at-a-glance health
• Subscores — which dimensions are strong/weak
• Notes (+) — positive signals
• Red flags (!) — concerns to investigate before adopting
• Recommendation — verdict (RECOMMENDED / LIKELY SUITABLE / ACCEPTABLE / CAUTION / BLOCK / RISKY)

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Scoring Model

Dimension	Max	What it measures	Key signals
Adoption	30	Is anyone using this?	all-time downloads, recent (90-day) downloads
Maintenance	25	Is it actively maintained?	last crates.io update, version count, GitHub last commit
Documentation	15	Can users learn it?	docs.rs build, description, docs URL, repo link
Maturity	15	Is the API stable?	age, stable version ≥1.0, has repo
Community	10	Is there a contributor base?	GitHub stars, contributors
License	5	Is it permissive?	permissive (MIT/Apache/BSD) preferred; copyleft penalized
Total	100

Grade bands

Grade	Score	Meaning
A	≥85	Excellent — recommended
B	70-84	Good — likely suitable
C	55-69	Acceptable — verify fit
D	40-54	Risky — investigate before use
F	<40	Avoid — significant concerns

See references/scoring-rubric.md for the full formula and signal weights.

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Red Flags Catalog

The tool surfaces specific concerns. Always read these before adopting.

Flag	Severity	Action
RustSec advisory	Block	Pin to fixed version or pick alternative
No release in >12 months	High	Check if abandoned; consider fork or alternative
Last GitHub commit >6 months	High	Activity may have moved elsewhere
No docs.rs build	Medium	API docs may be missing; check manually
License not declared	Medium	Treat as proprietary; cannot use without clarification
Low adoption with many versions	Medium	Churn without traction; investigate quality
Pre-1.0 with 20+ versions	Medium	API likely unstable across minor bumps
Single maintainer + low adoption	Medium	Bus factor risk; consider backing up or forking
No source repository	High	Cannot audit; avoid

See references/red-flags.md for the full catalog and decision guidance.

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Decision Shortcuts

Question	Answer
Which crate for X?	search "X", then compare top 3-4
Is this crate safe?	eval <name>; check red flags for advisories
Is it maintained?	eval <name>; check maintenance subscore + last update
Is the API stable?	eval <name>; check maturity subscore + version ≥1.0
What's the license?	eval <name>; appears in signals
A vs B vs C?	compare A B C; pick highest score without blocking red flags
Score says A but it doesn't fit my use case	Trust the fit check over the score — score measures health, not fitness

When the score is misleading

• Niche crates — a domain-specific crate may have low downloads but be the only option. Score will understate; rely on manual review.
• New crates — recent releases have low adoption signals; check maintainer track record instead.
• Forks — a fork may have few downloads but be the maintained successor. Check the parent crate's status.
• Internal/private crates — not on crates.io; this tool won't help. Use manual review.

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Resources

• Scoring Rubric — full formula, log-scale parameters, subscore breakdowns
• Red Flags Catalog — full flag list with severity and action
• API Endpoints Reference — the 4 data sources and their endpoints
• Evaluation Workflow Examples — worked scenarios (ORM choice, HTTP client, logging)
• scripts/crate_eval.py — the evaluation tool (run with python3)

Upstream Sources

• crates.io API — search, crate metadata, version downloads
• docs.rs — documentation build status, version presence
• GitHub REST API — stars, contributors, last commit, open issues
• RustSec Advisory Database — known vulnerabilities
• crates.io-index — registry index (alternative to API)