# Why Once You should not have to rebuild the same inputs just because the work moved from your laptop to continuous integration, or from one coding agent to another. Once makes that work reusable without asking you to replace every working tool in your repository first. The idea is simple: describe what an action reads, what it writes, and the environment it needs. Once gives that contract a content-based identity and stores the result. When the contract is unchanged, it restores the result instead of repeating the work. Build systems such as Bazel have demonstrated the value of explicit dependencies, shared caches, and remote execution. Once brings that model to existing repository automation through native project discovery, annotated scripts, and typed targets. The migration can start with one useful action, not a repository-wide rewrite. ## Agents Change The Shape Coding agents push against that model. They can run concurrently across worktrees, explore several fixes at once, retry tests, regenerate outputs, and ask for the same expensive setup from different sessions. Work that was annoying when one developer repeated it becomes wasteful when many agents repeat it in parallel. That changes what feels worth optimizing. The capabilities once associated with large enterprise build systems start to matter in ordinary repositories: stable action identities, deterministic inputs, reusable outputs, shared cache storage, and the option to run work somewhere other than the current laptop. ## Infrastructure Is Fragmenting At the same time, new caching and compute infrastructure is emerging to serve this need. Some providers focus on artifact storage. Some focus on remote execution. Some are tied to a build system, a continuous integration vendor, a cloud runtime, or an agent platform. The result is useful, but fragmented. Teams still need a way to describe what work should happen, what values affect it, which outputs matter, and what an agent can inspect while that work is running, without binding every automation workflow to one provider. ## Once Is The Narrow Waist Once is the [narrow waist](https://en.wikipedia.org/wiki/Hourglass_model) between automation needs and the infrastructure that can make those workflows faster. Above Once, developers and agents describe targets, capabilities, and actions. Each action declares its inputs, outputs, environment, working directory, runtime needs, and required provider capabilities. Providers can supply local cache storage, shared cache storage, or remote compute. Keeping that waist small matters. The action contract should be simple enough for agents to reason about, stable enough for providers to implement, and flexible enough for teams to keep using the tools they already have. Scripts and typed targets share the same action model. Scripts already encode real repository knowledge, so Once lets them enter that model immediately. When that work needs richer dependencies, multiple capabilities, structured diagnostics, or agent-driven edits, it can move into typed graph targets while keeping the same cache, build, run, and test workflow. ## What makes reuse trustworthy Caching is only correct when the action contract is complete. An undeclared file, a changing network response, or an untracked environment variable can make a recorded result stale. Once gives you explicit contracts and queryable plans, but it does not make an arbitrary command hermetic by default. Start locally, verify the inputs and outputs, and then share the result with your team. Move work to remote execution when its toolchain and runtime needs can be supplied by the chosen provider. This keeps performance improvements attached to a workflow you can inspect and trust. ## Next Continue with [Getting Started](/guide/getting-started) to install Once and reuse the result of a cacheable script. If running work away from the current computer is your main interest, read [Remote Execution](/guide/infrastructure/remote-execution).