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fx

fx is a native coding agent CLI from Vercel Labs. The fx project uses Zig and the Apache-2.0 license. The fx project status is experimental. AGRO installs the fx binary with the official installer from https://fx.sh/setup.sh. AGRO bakes no fx binary into the sandbox image.

Install​

Run the install command on the host or in the sandbox:

agro harness install fx

The command runs the upstream installer as the sandbox user. The installer writes the binary to ~/.local/bin in the persistent home volume. AGRO pins fx to version v0.0.13:

curl -fsSL https://fx.sh/setup.sh | FX_INSTALL_DIR="$HOME/.local/bin" bash -s v0.0.13

Verify the install:

fx --version
agro harness status fx

The fx --version command prints 0.0.13. See Harnesses Overview for the behavior of the verb when the sandbox is not running.

Uninstall​

agro harness uninstall fx

The command deletes ~/.local/bin/fx. fx keeps its credentials and settings in ~/.fx/. The command does not delete ~/.fx/. See Harnesses Overview → Removing a harness.

Authentication​

Sign in from a Herdr pane inside the sandbox. Use one of these commands:

CommandAccess
fx loginVercel AI Gateway
fx login codexChatGPT subscription (OpenAI Codex OAuth)
fx login grokGrok subscription (xAI OAuth)
fx setupVercel AI Gateway API key

fx also reads the AI_GATEWAY_API_KEY environment variable. AGRO stores no fx credential.

These commands work without credentials:

fx status --json
fx doctor --json

When no credential exists, both commands report "auth":"missing".

Common usage​

fx                                                # start an interactive session
fx ask "explain the changes in this repository"   # run a one-shot prompt

In an interactive session, type /help to list the interactive commands.

Run interactive sessions in Herdr, so that a session survives a disconnect. Run agro tool install herdr, then run herdr, then start fx in a pane.

AGRO integration​

Project instructions​

fx loads the root AGENTS.md from the start directory. When fx works on a file, fx also loads each nested AGENTS.md that applies to the target file. The closest file wins a conflict. This rule matches the AGRO rule for target-path specificity. AGRO adds no fx instruction file and no .fx.json.

Skills​

fx discovers AGRO skills through .agents/skills and .claude/skills. Both links resolve to .agro/skills:

.agents/skills -> ../.agro/skills
.claude/skills -> ../.agro/skills

fx checks .claude/skills before .agents/skills. fx resolves each skill directory to its real path and keeps the first copy of each directory. Each AGRO skill appears once, with .claude/skills as its source. fx merges only copies of the same directory. Two separate directories with the same skill name both appear. Source: src/builtins/skills.zig and src/core/skills/skill_runtime.zig in vercel-labs/fx.

.agro/scripts/link-providers.sh creates and repairs both links. AGRO adds no .fx/skills link.

MCP servers​

fx reads the project MCP configuration. Run fx status --json to list the MCP servers that fx found.

fx does not start a project MCP server until the operator approves it. fx ask skips an unapproved project server and prints skipped unapproved project MCP servers: <name>. Approve a server with fx mcp trust approve <name>.

Hooks and guards​

AGRO hooks in .agro/hooks/ do not run under fx. The cc-safety-net command hook also does not run under fx. fx has no user-configured command hook. These AGRO guards are absent under fx:

  • deny-env-dump.sh
  • deny-secret-paths.sh
  • warn-devtcp.sh
  • notify_slack.sh
  • cc-safety-net
Absent guards

Under fx, no AGRO guard examines a command or a file path before fx runs the command or reads the file. The Docker sandbox is the security boundary. fx permission rules live only in ~/.fx/settings.json. A project file cannot set fx permission rules.

Herdr​

fx reports its state to Herdr through its built-in Herdr provider. AGRO adds no Herdr configuration for fx.

References​