Declare the inputs and outputs of cached builds

Make build-cache contracts cover the actual files and configuration consumed and produced by the task.

Prompt

Evaluate and apply this CI technique to my repository: Declare the inputs and outputs of cached builds.

Make build-cache contracts cover the actual files and configuration consumed and produced by the task.

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

Make build cache keys describe the build

Mastra declared source, package and compiler configuration inputs for library builds, excluding test files and Markdown where they were not build inputs. Composite tasks received their own input declarations.

Use it when: A remote build cache misses after edits that leave the emitted artifact unchanged.
Before applying it: Exclusions must match actual tools, generators and imported assets.

Declare every input and output of expensive transforms

The Java SDK declared the R8 program, rule and JDK inputs and both the transformed JAR and mapping outputs, so Gradle restores the result when inputs match. Both executable compatibility smoke tests still run.

Fixture command on local JDK 21: 45s to 3s with the outputs restored Source

Use it when: A build task reruns an expensive transformation on unchanged inputs.
Before applying it: An undeclared input serves stale output. Toolchain paths can limit reuse across machines, and the cache needs a trusted writer.

How companies used this technique

Make build cache keys describe the build

Declare every input and output of expensive transforms

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