Reuse downloaded tools across runs

Cache versioned tools and browser downloads so jobs can restore them while retaining installation and repair checks.

Prompt

Evaluate and apply this CI technique to my repository: Reuse downloaded tools across runs.

Cache versioned tools and browser downloads so jobs can restore them while retaining installation and repair checks.

Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/cache-tool-downloads.md

Inspect this repository’s CI workflows, build and test commands, dependencies, and recent run timings. Identify where this technique applies and explain the expected benefit using this repository’s evidence.
Measure a baseline from recent comparable runs: elapsed time, queue time, runner minutes and failures where available. If data is unavailable, say what cannot be measured.
Compare relevant company approaches, checking prerequisites, platform differences and tradeoffs. Rank applicable options by evidence, fit and measurable opportunity; do not present company results as predictions for this repo.
Recommend the smallest safe change, show what checks and fallback paths remain, and ASK ME WHICH CHANGE TO APPROVE BEFORE EDITING ANY FILES.
Only after approval, work on a new feature branch, make one reversible change, and open a reviewable pull request. Never merge or push to a default or protected branch.
Keep required checks, test coverage, deployment and release behavior intact. Validate the change and compare equivalent runs where possible; report limitations and what should be monitored after merge.

View all playbooks

How companies used this technique

Read what each company changed and follow the original sources.

Cache compiled lint tools between runs

Bun cached the cargo-dylint binaries on the tool version, and the dylint driver and mordant library on the version plus the pinned mordant revision. A cache hit skips only the install; the workspace check still runs on every change. The cache carried over when Bun folded its Rust lint jobs into one workflow.

A cold run takes about 6.5 minutes; the PR expects warm runs to take about a minute and a half (estimate). Source

Use it when: Installing or compiling a lint tool takes a large share of the lint job.
Before applying it: The cache key covers the runner OS, the tool version and every pinned revision the tool is built against.

Cache pinned tool and matrix downloads

The same SDK change caches the npm downloads of a version-pinned npx tool and of each smoke-test matrix leg, with keys that name the tool version or the matrix’s Node and TypeScript versions.

Use it when: A pinned command-line tool or matrix leg downloads the same packages on every run.
Before applying it: OPT2’s recipe targets large binaries; here its version-pinned cache key applies to npm package downloads. Key the cache on every version that changes the download, and keep the step that installs or runs the tool.

Reuse browser downloads and keep the repair step

Checkout Kit caches Playwright Chromium in its default Linux cache directory, keyed by the runner's operating system and the web lockfile. The install command still runs after the restore, so it repairs a stale or partial cache and installs system dependencies.

Merged 2026-10-12; the cache step is on the default branch. Source

Use it when: Browser downloads take a large share of a job's setup on every run.
Before applying it: A browser cache can take as long to restore as a fresh download; compare cold, warm and changed-lockfile runs before keeping it.

Reuse a downloaded toolchain

Stripe Android replaced its Java installer with direct Temurin downloads for the configured version, OS and architecture, and reuses an existing install directory on later builds.

Use it when: Every CI job repeats a large toolchain download or installer bootstrap.
Before applying it: Key the reuse on exact version, OS and architecture, verify a published checksum, and install atomically so a partial download is never reused.

How companies used this technique

Cache compiled lint tools between runs

Cache pinned tool and matrix downloads

Reuse browser downloads and keep the repair step

Reuse a downloaded toolchain

Related techniques

Bake stable dependencies into runner images

Cache package downloads and dependency stores

Cache the directories the build actually uses

Company Playbooks

Related guides

Cache workflow dependencies

Cut repeated test setup

Share setup steps across jobs

Optimize npm installs

Optimize pnpm installs