# phax > phax runs a plan through AI coding agents — Claude Code, OpenAI Codex or Mistral Vibe — as a sequence of gated phases, and hands you a change you can review. ## Guide - [Installation](https://docs.phax.run/guide/install.md): Install the phax CLI with npm (@lbdremy/phax), a launcher that fetches and caches the binary for your platform, and set up shell completions. - [How phax works](https://docs.phax.run/guide/concepts.md): Specs and plans and their lifecycle, runs and phases in Git worktrees, gates, handoffs, reconciliation, review, records and where phax keeps its state. - [Project setup](https://docs.phax.run/guide/set-up.md): Set up a repository for phax: phax init writes phax.json with your project's name, its gate commands, and whether runs are reviewed and published. - [Writing specs and plans](https://docs.phax.run/guide/specs-and-plans.md): Write a spec and a plan with your agent or headless from a brief, lint and approve them, and follow their status from Draft to Completed. - [Running a plan](https://docs.phax.run/guide/run.md): Run an approved plan with phax run: each phase in its own Git worktree, held by your gates, fixed by the same agent session when a gate fails. - [Reviewing and landing](https://docs.phax.run/guide/review-and-land.md): Review a finished run: its review handoff, the compliance review against the plan, phax review-code, then publish-pr opens the pull request. - [Run records](https://docs.phax.run/guide/records.md): Records keep a run's history: one commit per phase on phax/records/v1, with its manifest, gate results, file reconciliation, diff and handoff. - [Agents and security](https://docs.phax.run/guide/providers-and-security.md): Run phases with Claude Code, OpenAI Codex or Mistral Vibe: how phax routes a model to a provider, and the security modes that sandbox each agent. - [Extending phax](https://docs.phax.run/guide/extend.md): Plug your own tools into a run: gate steps that return findings, a brief provider that answers each phase, and a plan auditor. - [When something goes wrong](https://docs.phax.run/guide/troubleshooting.md): Fix a run that went wrong: a gate that keeps failing, a phase to start over, and phax report to open an issue with the run's telemetry. - [Deciding open questions](https://docs.phax.run/guide/arbitration.md): Decide open questions with phax artifact decide: framing first, then each question under a doctrine, and the body diff accepted before writing. - [Upgrading phax](https://docs.phax.run/guide/upgrading.md): Upgrade phax, refresh the skills and phax.schema.json it copied into your repository, and the one-time steps each release asks for. - [Troubleshooting a failed agent session](https://docs.phax.run/guide/agent-session-failures.md): Read a failed agent session's cause, files and retry hint, and what to do for exit 5, 8 and 14. - [Structured answers and providers](https://docs.phax.run/guide/structured-answers.md): What Claude Code, Codex and Mistral Vibe each check of a structured answer, what phax checks after them, and the one corrective resume. - [Estimating a plan](https://docs.phax.run/guide/plan-estimate.md): Estimate a plan's API-list cost from your cost ledgers with phax plans estimate, and whether it fits your Claude subscription windows now. - [Reading a plan's overview](https://docs.phax.run/guide/plan-overview.md): See a plan phase by phase before you approve or run it: planned files by architecture part, acceptance pairs, test lines and its spec's criteria coverage. - [Architecture provider](https://docs.phax.run/guide/architecture-provider.md): Declare a command that answers phax architecture with your repository's architecture, and the limits it runs under when a planner calls it. - [Acceptance phases](https://docs.phax.run/guide/acceptance-phases.md): Declare an acceptance provider, and write a plan whose acceptance tests are written in one phase and passed in a later one. - [Assignment bounds](https://docs.phax.run/guide/assignment-bounds.md): Bound which model and efforts a phase takes where it touches certain files, and how phax plans lint and phax run hold plans to the bounds. ## Reference - [File formats](https://docs.phax.run/reference/formats.md): The files phax writes, each named by its $schema URL on docs.phax.run, and @lbdremy/phax-schemas to read them from your own code. - [Exit codes and environment](https://docs.phax.run/reference/exit-codes.md): What each phax exit code means, the subset phax prune uses, and why phax reads its configuration from files rather than environment variables. - [CLI reference](https://docs.phax.run/reference/cli.md): Every phax command with its flags and arguments: artifacts, plans, runs, review and publishing, records, and the read-only commands. - [Machine answers](https://docs.phax.run/reference/json-output.md): What --json writes on stdout, the message lines on stderr, the refused and defect exit codes and what --json-schema prints, for agents and scripts. - [Model catalog](https://docs.phax.run/reference/model-catalog.md): The models phax routes to on Claude Code, OpenAI Codex and Mistral Vibe, their effort levels, and the default model behind each of phax's own jobs. ## Security - [Security](https://docs.phax.run/security.md): How phax keeps coding agents safe by default: provider-native sandboxes, its three security modes, their configuration and how to verify them. ## Compare - [OpenSpec vs. phax](https://docs.phax.run/compare/openspec-vs-phax.md): OpenSpec vs. phax, side by side: OpenSpec structures the spec conversation; phax runs the approved plan through coding agents in gated phases. - [Spec Kit vs. phax](https://docs.phax.run/compare/spec-kit-vs-phax.md): Spec Kit vs. phax, side by side: a methodology and prompt layer that runs your agent step by step, against a harness of gated, reviewable phases. - [phax and agentic practice](https://docs.phax.run/compare/agentic-practices.md): Where phax stands against the agentic engineering practices the literature names: what it covers, what it covers in part, and what it does not do yet. ## Releases - [phax 0.35.0](https://docs.phax.run/releases/0-35-0.md): What phax 0.35.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.34.0](https://docs.phax.run/releases/0-34-0.md): What phax 0.34.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.33.0](https://docs.phax.run/releases/0-33-0.md): What phax 0.33.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.32.0](https://docs.phax.run/releases/0-32-0.md): What phax 0.32.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.31.0](https://docs.phax.run/releases/0-31-0.md): What phax 0.31.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.30.0](https://docs.phax.run/releases/0-30-0.md): What phax 0.30.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.29.0](https://docs.phax.run/releases/0-29-0.md): What phax 0.29.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. - [phax 0.28.0](https://docs.phax.run/releases/0-28-0.md): What phax 0.28.0 changes: the specs and plans it delivers, its fixes and its upgrade steps. ## Others - [Contributing](https://docs.phax.run/contributing.md): Work on phax itself: the checks and test tiers, the state machine, telemetry, the CLI contract, the binary and how releases are cut. - [Releasing](https://docs.phax.run/contributing/release.md): Cut a phax release: SSH signing, the trusted publisher, cutting and tagging, the release workflow, staged npm packages and the docs site deploy.