---
name: phoenix-cli-development
description: >
  Design and implementation guide for the Phoenix CLI (`px`). Covers the noun-verb command structure,
  dual-audience design (humans and coding agents), Commander.js patterns, configuration resolution,
  output formats, exit codes, and conventions for adding or modifying commands. Triggers when
  working on phoenix-cli commands — adding new commands, modifying existing ones, refactoring command
  structure, or reviewing CLI code. Also triggers on mentions of `px` commands, CLI design,
  or adding a new resource to the CLI.
license: Apache-2.0
metadata:
  author: oss@arize.com
  version: "2.1.0"
  internal: true
---

# Phoenix CLI Design Specification

The Phoenix CLI (`px`) is a command-line interface for the Phoenix AI observability platform. It serves two distinct audiences simultaneously: **humans** typing commands in a terminal and **coding agents** (Claude Code, Cursor, Codex, Gemini CLI) executing commands programmatically.

This specification uses RFC 2119 keywords (MUST, SHOULD, MAY, etc.) to indicate requirement strength.

## Command Structure: Noun-Verb

All commands MUST follow a **noun-verb** pattern, modeled after the GitHub CLI (`gh`):

```
px <resource> <action> [arguments] [options]
```

Resource names MUST be **singular** — they name the type of thing you're acting on, not how many:

```bash
px project list              # not "px projects"
px project create            # not "px create-project"
px trace get <trace-id>
px dataset get <name-or-id>
px auth status
```

### Standard verbs

Commands SHOULD use these verbs consistently across all resources:

| Verb     | Purpose                       | Takes argument? | Example                             |
| -------- | ----------------------------- | --------------- | ----------------------------------- |
| `list`   | List/query multiple resources | No (uses flags) | `px project list --limit 10`        |
| `get`    | Fetch a single resource by ID | Yes (required)  | `px trace get <trace-id>`           |
| `create` | Create a new resource         | Varies          | `px project create --name foo`      |
| `update` | Modify an existing resource   | Yes (required)  | `px project update <id> --name bar` |
| `delete` | Remove a resource             | Yes (required)  | `px project delete <id>`            |

Not every resource supports every verb — datasets MAY omit `create` via CLI if the primary flow is through the SDK. Commands SHALL only add verbs that make sense for the resource.

Additional verbs for specialized actions are RECOMMENDED when the standard set doesn't cover it:

- `px auth login`, `px auth status`
- `px self update`
- `px docs fetch`
- `px api graphql <query>`

### Backward compatibility during migration

The CLI is evolving from a flat structure (`px projects`, `px traces`) toward full noun-verb. During the transition, both forms MAY coexist. When migrating an existing command:

1. The new noun-verb form MUST be created as the primary command
2. The old form SHOULD be kept as a hidden alias (Commander's `.alias()` or a hidden command) so existing scripts don't break
3. Only the noun-verb form SHALL be documented going forward

## Dual-Audience Design

The CLI MUST be equally usable by a person at a terminal and by a coding agent. Every command that outputs data MUST support `--format`:

- **`pretty`** (default) — Human-readable tables and formatting
- **`json`** — Indented JSON for human inspection of structured data
- **`raw`** — Compact single-line JSON for piping into `jq` or agent consumption

Commands MAY support additional formats (e.g., `--format text` for prompts). The default MUST always be `pretty`.

Progress indicators MUST write to stderr. Agents SHOULD pass `--no-progress` to suppress them.

```bash
# Agent-friendly invocation
px trace list --format raw --no-progress | jq '...'
```

### Semantic exit codes

Defined in `src/exitCodes.ts`. Commands MUST use the named constants and MUST NOT use bare numeric literals.

| Code | Constant           | Meaning                                             |
| ---- | ------------------ | --------------------------------------------------- |
| 0    | `SUCCESS`          | Command completed successfully                      |
| 1    | `FAILURE`          | Unspecified or unexpected error                     |
| 2    | `CANCELLED`        | User cancelled (e.g., declined a confirmation)      |
| 3    | `INVALID_ARGUMENT` | Bad CLI flags, missing required args, invalid input |
| 4    | `AUTH_REQUIRED`    | Not authenticated or insufficient permissions       |
| 5    | `NETWORK_ERROR`    | Failed to connect to server or network request      |

### Interactive default with non-interactive mode

Commands MAY prompt interactively when a required value is missing or a confirmation is needed — this is the human-friendly default. The `--no-input` flag MUST suppress all prompts: both missing-value prompts and destructive-action confirmations. Non-interactive mode is also activated automatically when no TTY is attached (piped stdin).

In non-interactive mode, if a required value is missing, the command MUST exit immediately with `ExitCode.INVALID_ARGUMENT` and print the correct invocation. If a confirmation would have been shown, the command MUST proceed as if confirmed:

```bash
# Human: missing --name triggers interactive prompt
px project create

# Agent: all inputs as flags, no prompts
px project create --name my-project --format raw --no-input

# Human: gets "Are you sure?" prompt
px dataset delete my-dataset

# Agent: skips confirmation
px dataset delete my-dataset --no-input --format raw
```

```
Error: Missing required flag --name.
  px project create --name <project-name>
```

### Idempotent commands

Commands SHOULD be idempotent where possible. Running the same command twice MUST NOT produce duplicate resources or unexpected errors:

- `create` commands SHOULD support `--if-not-exists` to return the existing resource instead of failing
- `delete` commands on a missing resource SHOULD exit with `ExitCode.SUCCESS` (not an error)

### Return structured data on success

Mutating commands (`create`, `update`, `delete`) MUST return the affected resource in the selected `--format` on stdout. Commands MUST NOT print bare success messages like "Project created." — output the resource so agents can extract IDs, URLs, and other fields:

```bash
$ px project create --name foo --format raw
{"id":"proj_abc","name":"foo","createdAt":"2025-03-15T10:00:00Z"}
```

### Fail fast with actionable errors

When a command fails due to invalid input, the error message MUST include the correct invocation syntax. Follow the pattern established by `getConfigErrorMessage()` in `src/config.ts`:

- Show what was wrong
- Show the correct command to fix it
- Suggest a related command when helpful (e.g., "Available projects: `px project list`")

When `--format raw` or `--format json` is active, errors SHOULD also be written as structured JSON to stderr so agents can parse them. Use the `StructuredError` shape:

```typescript
interface StructuredError {
  error: string; // Human-readable error message
  code: string; // ExitCode constant name (e.g., "INVALID_ARGUMENT")
  hint?: string; // Suggested command to resolve the issue
}
```

```json
{
  "error": "Project not found",
  "code": "FAILURE",
  "hint": "px project list --format raw"
}
```

### Progressive help discovery

Every subcommand MUST include a `--help` with at least one concrete example. Use Commander's `.addHelpText('after', ...)` to append an `Examples:` block:

```
$ px project create --help
Usage: px project create [options]

Create a new Phoenix project.

Options:
  --name <name>       Project name (required)
  --description <d>   Project description
  --format <format>   Output format (pretty|json|raw) (default: "pretty")
  -h, --help          Display help

Examples:
  px project create --name my-project
  px project create --name my-project --format raw
```

Agents discover capabilities incrementally: `px` → `px project` → `px project create --help`. Each level MUST provide enough information to navigate deeper.

## Adding a New Command

### Options interface

Every handler MUST define a TypeScript interface for its options. Field names MUST be descriptive — abbreviations MUST NOT be used. Common options that appear across many commands:

```typescript
interface CommonOptions {
  endpoint?: string; // --endpoint: Phoenix API endpoint override
  apiKey?: string; // --api-key: API key override
  project?: string; // --project: Project name or ID override
  format?: OutputFormat; // --format: Output format (pretty/json/raw)
  progress?: boolean; // --no-progress: Suppress progress indicators
}
```

Commands that prompt for input or confirmation MUST support non-interactive mode:

```typescript
interface InteractiveCommandOptions extends CommonOptions {
  noInput?: boolean; // --no-input: Suppress all prompts
}
```

### Configuration resolution

The CLI MUST resolve configuration from multiple sources. Use `resolveConfig()` from `src/config.ts` for this merge logic. Priority:

1. **CLI flags** (highest priority) — `--endpoint`, `--api-key`, `--project`
2. **Environment variables** — `PHOENIX_HOST`, `PHOENIX_API_KEY`, `PHOENIX_PROJECT`
3. **Defaults** — `http://localhost:6006` for endpoint

Command handlers MUST NOT read environment variables directly.

### Output formatting

Each resource type SHOULD have formatting modules in `src/commands/format*.ts`. When creating a new resource command, a corresponding formatter MUST be created following the existing pattern.

- `formatTable.ts` — Shared table rendering with terminal-width-aware column truncation
- `formatProjectsOutput()`, `formatTracesOutput()`, etc. — Resource-specific formatters

Formatters MUST accept a `format` option and return a string.

### I/O functions

Commands MUST use the helpers from `src/io.ts`:

```typescript
writeOutput({ message }); // → stdout (data the user/agent wants)
writeError({ message }); // → stderr (errors)
writeProgress({ message, noProgress }); // → stderr (suppressible status updates)
```

`console.log` MUST NOT be used directly. The `writeOutput`/`writeError` split ensures stdout contains only data output, which is REQUIRED for piping correctness.

## Naming Conventions

Code MUST follow these naming conventions (see also the phoenix-typescript skill):

- **Functions and variables**: `camelCase` — `createProjectCommand`, `projectListHandler`
- **Types and interfaces**: `PascalCase` — `ProjectListOptions`, `OutputFormat`
- **Constants**: `SCREAMING_SNAKE_CASE` — `ExitCode.SUCCESS`, `CLI_VERSION`
- **Files**: `camelCase.ts` — `projects.ts`, `formatProjects.ts`
- **No abbreviations** — `projectIdentifier` not `projId`, `annotationConfig` not `annCfg`

## Testing

Tests use **vitest** and live in the `test/` directory, mirroring `src/` structure.

```bash
pnpm test          # run all tests
pnpm test:watch    # watch mode
```

When adding a command, tests MUST cover:

- The handler logic (mocking the Phoenix client)
- Formatter output for each format mode
- Edge cases: missing config, network errors, empty results
- Exit code correctness for error paths

## Build and Run

```bash
pnpm build         # TypeScript → build/
pnpm dev           # Run from source via tsx (during development)
```

The CLI is published as `@arizeai/phoenix-cli` with binary aliases `px` and `phoenix-cli`.

## Global Options Placement

Global options (`--endpoint`, `--api-key`) MUST be placed on the **verb**, not the noun. This is REQUIRED because Commander attaches options to the command that defines them:

```bash
# Correct — options on the verb
px project list --endpoint http://my-server:6006

# Wrong — options on the noun (Commander won't parse these)
px project --endpoint http://my-server:6006 list
```

## Checklist for Adding a New Resource Command

1. Create `src/commands/<resource>.ts` with `create<Resource>Command()` exporting the noun
2. Add verb subcommands (`list`, `get`, `create`, etc.) as needed
3. Create `src/commands/format<Resource>.ts` for output formatting
4. Define options interfaces with descriptive field names
5. Use `resolveConfig()` for configuration, `createPhoenixClient()` for API calls
6. Use `writeOutput()`/`writeError()` for I/O, semantic `ExitCode` constants for errors
7. Export from `src/commands/index.ts`
8. Register in `src/cli.ts` via `program.addCommand()`
9. Add tests in `test/`
10. Run `pnpm test` — fix any failures before proceeding
11. Run `pnpm build` — fix any type errors before proceeding
12. Update `README.md` with usage examples showing both human and agent-friendly invocations
13. Update the external Phoenix CLI skill at `.agents/skills/phoenix-cli/SKILL.md` when commands, flags, examples, or output shapes change
14. Keep skill updates concise: document the new capability with the smallest useful examples and output-shape notes rather than repeating the full README
15. If the command prompts for input or confirmation, support `--no-input` (see `InteractiveCommandOptions`)
16. Add at least one example to `--help` via `.addHelpText('after', ...)`
17. Mutating commands return the affected resource on stdout (not just a success message)
18. Run manually with `--format raw` and `--no-input` to verify agents get clean, parseable output