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:

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.

# 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:

# 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:

$ 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:

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
}

{
  "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:

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:

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:

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.

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

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:

# 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