Choose Dependency

Choosing a dependency

Every dependency is a trade, and the obvious heuristics pull in opposite directions. Balance them deliberately.

• Force A — fewer dependencies is better. Each third-party library is attack surface, a supply-chain risk, transitive bloat, a thing that can break or go unmaintained, and a version to track. The standard library is always the first choice; a pile of micro-dependencies is a smell.
• Force B — don't reinvent the wheel. A library delegates a whole problem's maintenance to its owner. Hand-rolled helpers for solved, non-trivial problems are our bug surface and our maintenance burden forever, so prefer a good external library to an internal reimplementation of something already well-solved.

These resolve into one rule:

Import rarely; when you do, pick the broad, trusted, well-maintained option and consolidate on it. A batteries-included library from a reputable source that covers a whole domain beats a thin wrapper that you'll have to supplement with three more libraries later. Fewer, better, broader dependencies — not more, smaller ones.

Illustration. Prefer an ORM like bun (struct decoding, query building, migrations, hooks all native, one maintainer) over a lower-level driver like pgx that needs extra third-party packages bolted on for the same ergonomics: one broad, well-maintained dependency replaces several narrow ones, fewer versions to track and one place to learn. Follow the reasoning pattern — pick per the actual need, not by analogy.

The decision procedure

Work top to bottom; stop at the first answer that fits.

1. Is it already solved in-house? Standard library, a dependency already in go.mod / package.json, or golib / nodelib? Use that. Adding a second library to do what an existing one already does is the most common avoidable dependency.

2. Is it trivial and stable? A few lines, well-understood, unlikely to change (a tiny string helper, a constant, a one-off transform)? Implement it internally — a dependency is not worth the supply-chain and version cost here. (For Go libraries, also weigh write-go-kit's "should this even live in golib?" bar.)

3. Is it a solved, non-trivial domain? Parsing, crypto, ORM/SQL, HTTP routing, validation, serialization, UUID, time, retries, observability, etc. — these are where you buy, not build; reimplementing them is how subtle bugs and security holes get in. Go to candidate evaluation.

4. Is it genuinely novel to our domain? No good library exists, or every candidate fails evaluation? Implement internally — and design it so it could graduate into a library later (write-go-kit).

Evaluating candidates (when buying)

Research each serious candidate against these, and write the comparison into the plan's build-vs-buy section. The first three are gating; the rest are tie-breakers.

• Trust — who owns it? A reputable org, a foundation, or a healthy community beats a single unknown maintainer. Trust is what makes "delegate the maintenance" safe.
• Maintenance & health — recent commits and releases, issues triaged, not archived, a real changelog. An abandoned library is an internal implementation you don't control.
• Security — known CVEs / advisories, the size and trustworthiness of the transitive dependency tree (a "small" library that drags in 40 packages isn't small), and supply-chain hygiene (signed releases, pinned CI).
• Coverage — does it cover enough of the domain that you won't need to add more libraries alongside it? This is the consolidation lever; weight it heavily.
• License — compatible with the repo's license and distribution. A blocker if not.
• Footprint & fit — binary/bundle size, API ergonomics that match our patterns, and how cleanly it isolates behind our own abstractions if we ever need to swap it.
• Adoption — popularity is corroborating evidence of trust and longevity, not a goal in itself.

Research method — use the internet, from trusted sources

Never decide from memory. Search the web and read primary, trustworthy sources:

• The library's official docs and repository (README, changelog, release cadence, open issues).
• The package registry — pkg.go.dev (Go), npmjs.com (JS) — for versions, dependents, and the transitive tree.
• Security advisories — GitHub Advisory Database, the Go vulnerability database, npm audit data.
• Reputable comparisons and the broader community's experience — weighted below primary sources, and always sanity-checked against the repo itself.

Prefer recent, primary information over old blog posts, and note your sources in the plan so the human can verify the call.

Org policy hooks

• No replace directives; exact version pins. Go deps are pinned to released tags and bumped by Renovate — see manage-versions.
• Internal (a-novel / a-novel-kit) dependencies are a manage-versions concern: SHA-pin while developing, dependency releases first, consumer re-pins to the tag before merging.
• Tooling dependencies (generators, linters, test tools) stay isolated in their own <tool>.mod / .sum files, never in the main go.mod, and are never go install-ed globally — see write-go's tools policy.
• Kit repos hold a stricter bar than services for taking on any dependency (write-go-kit).

Output

A short, justified recommendation that drops into the plan's build-vs-buy section: the need, the options weighed (stdlib / existing / a named library / internal), the evaluation evidence with sources, and the call with its reasoning. If the answer is "build internally," say why every buy option fell short; if "buy," say why this library and not the narrower alternatives.

Examples

Build. Need: a 15-line helper that formats an internal ID into a display string, specific to our domain. No external library matches without contortions, the logic is trivial and stable. Implement it internally — a dependency here would add supply-chain risk for nothing.

Reuse. Need: structured logging in a new service. golib already exposes the org's logging setup. Use it — adding a different logging library would fragment the codebase and duplicate a solved concern.

(The buy-and-consolidate case is the bun-over-pgx illustration above.)