CLI For Agents

CLI For Agents

Build CLIs as one engine with two renderers:

• human mode: readable text or TUI
• agent mode: deterministic JSON or NDJSON

Do not maintain separate doctrine for the two audiences. Keep one command model and one source of truth, then render it differently.

Use When

• designing a new CLI
• reviewing an existing CLI for agent compatibility
• adding commands, flags, or help text
• building watch/status/list commands that must work for both humans and agents
• tightening tests or guardrails around CLI output shape

Core Model

Dual-audience design

• Separate data production from presentation.
• The same command should support both human-readable and machine-readable output.
• Prefer --json for bounded results and --ndjson for streams or watch modes.
• If a TUI exists, provide a non-TUI path for the same command.

Examples:

# Human
mycli watch --task abc123

# Agent
mycli watch --task abc123 --ndjson --no-tui

Canonical behavior

• The machine-readable mode is not a second implementation.
• Do not let TUI logic become the only place where important state transitions exist.
• The CLI should emit the same underlying facts in both modes.

Stable contract model

• Treat --json as the stable contract for agents, scripts, and tests.
• Human-formatted output may change as wording, spacing, and styling improve.
• If a command is consumed programmatically, say so explicitly in help:
  • script against --json
  • human output may change

Bounded default output

Protect the context window

• Default output must be the minimum useful response, not the maximum available data.
• Pre-sort items so the most important rows appear first.
• Truncate long fields by default.
• Require explicit opt-in such as --full, --verbose, or --raw for large payloads.
• Preserve critical head and tail context when truncating command output.

Bad:

mycli list
# dumps every row and every field

Good:

mycli list
# top items only, scoped fields only

mycli list --full
# full payload

Progressive disclosure

Prefer graduated retrieval over one-shot dumps:

• list or search for routing
• summary for bounded orientation
• show --section <name> for targeted expansion
• show --full only by explicit opt-in
• Discovery responses should stay routing-sized. A good default JSON envelope is:
  • status
  • query
  • count
  • results
  • schema_version
  • next_step when it makes the cheapest follow-up obvious
• Bounded reads should report how resolution happened when the command accepted natural input. Use fields such as matched_on or resolved_from so agents know whether they are operating on an exact ID or a search-resolved target.

If a CLI owns rich documents, logs, or traces, build commands around:

summary -> section -> full

This is better for both humans and agents than dumping the entire surface by default.

Structured discoverability

• Root help should group commands by job, not alphabetically.
• Mark likely entry points with hints like start here.
• Prefer command families that separate:
  • discovery
  • resolve
  • read
  • write
• Every command should define:
  • short summary: 5-10 words, starts with an action verb
  • long description: what it does, when to use it, how it differs from nearby commands
  • examples: 3-5 concrete copy-pasteable invocations
• Examples matter more than prose. Agents infer flag shape from examples.

Example layout:

Task Management:
  send        Send a message to start or continue a task (start here)
  watch       Subscribe to live updates for a running task
  get         Retrieve the current state of a task

Discovery:
  describe    Inspect identity, skills, and capabilities

For repeated external-service, archive, or admin workflows, aim for:

doctor      Verify setup, auth, version, and reachability
discover    Find top-level resources or containers
resolve     Turn names, URLs, or slugs into stable IDs
read        Fetch exact objects or bounded lists
write       Perform one named mutation with preview or dry-run support
request     Raw escape hatch

Metadata quality is routing quality

• Titles, summaries, tags, and identifiers determine what an agent loads next.
• Short descriptions must be specific, not generic boilerplate.
• Result-card summaries and longer detail summaries should be distinct.
• Tags should be deterministic and meaningful, not inferred freeform when routing quality matters.
• Cross-links between related entities or docs should be deliberate, not opportunistic.

If the CLI returns knowledge-like records, every item should have:

• a strong title
• a bounded short summary
• optional deeper summary or section handles
• useful tags or categories
• adjacent links or next-hop identifiers when available

Agent-first interoperability

doctor is first-class

• Durable agent-facing CLIs should expose a doctor or equivalent command.
• doctor --json should verify config, auth source, version, endpoint reachability, and missing setup.
• If offline or fixture mode exists, doctor --json should report that explicitly instead of failing ambiguously.
• Later tasks should be able to run tool-name --json doctor first without reading docs.

Non-interactive first

• Every required input must be expressible as a flag, stdin, or positional argument.
• Interactive prompts are fallback only, never the default requirement.
• Respect NO_COLOR and [APP]_NO_TUI environment variables.
• When stdout is piped, suppress TUI, prompts, spinners, and decorative color.

--json on everything that returns data

• Commands that return data should support --json.
• Keep machine output bounded too; large structured payloads still need scoping.
• Prefer --ndjson for streaming or watch commands.
• Never force agents to scrape tables or prose when the command already knows the schema.
• Do not return silent false-positive success payloads for misses. If resolution fails, return a deterministic error shape with retry guidance and, when possible, ranked suggestions.

Pipelines and stdin

• Accept stdin when composition is natural.
• Support - as stdin where appropriate.
• Let one command feed the next without requiring temp files.

Examples:

mycli search "stalled tasks" --json | mycli rerank --stdin
mycli build --json | mycli deploy --spec-json -

Discover, then resolve, then read

• Discovery commands should return bounded lists with stable handles.
• Resolve commands should convert human input such as names, URLs, slugs, or permalinks into canonical IDs.
• Read commands should accept those stable IDs directly.
• Do not force agents to repeat broad searches when an exact read can follow a resolve step.
• If a command accepts natural-language input directly, let summary or read auto-resolve obvious first-try matches and expose the resolution mode in machine output.
• Multi-word natural queries should not require brittle quoting if the command intent is retrieval rather than mutation.

Headless authentication

• Agents cannot complete browser auth flows reliably.
• Support headless auth such as env vars, tokens, service accounts, or pre-authenticated config.
• If interactive auth is unavoidable, fail immediately with a clear actionable hint.
• Never hang waiting for a browser login when running in no-TUI or machine-readable mode.

Mutative safety

• Mutating commands should support --dry-run.
• Commands with confirmations should offer --yes or --force.
• Default behavior should remain safe for humans.
• Repeat successful operations safely: no-op or explicit already done beats duplicate side effects.

Error guidance

• Fail fast on invalid flags, missing config, missing auth, or missing prerequisites.
• Print exact next-step commands in errors.
• Emit errors to stderr.
• Return deterministic exit codes:
  • 0 success
  • 1 general failure
  • 2 invalid usage
  • 3 auth or connectivity failure

Example:

Error: database not initialized
Hint: run 'mycli init' to create the local database

Success output

• Successful commands should return machine-useful identifiers and next-hop values.
• Plain text is fine for human mode, but avoid decorative output as the only success signal.

Example:

deployed v1.2.3 to staging
url: https://staging.myapp.com
deploy_id: dep_abc123
duration: 34s

Config and environment

• Prefer standard config locations and explicit environment selection.
• Support named environments like --env local|staging|prod.
• Let agents switch environments without knowing raw URLs or tokens.

Visual design

• Color should communicate state, not decorate prose.
• Prefer semantic colors:
  • accent: headers, landmarks
  • command: command names and flags
  • pass: success
  • warn: warnings or pending
  • fail: errors
  • muted: metadata
  • id: identifiers
• Whitespace and alignment should carry hierarchy more than color.
• When formatting tables with ANSI colors, pad before styling or use a layout engine that handles colored strings safely.

Enforcement inside the CLI

These are the highest-value behaviors to enforce in code, not just document:

• stdout piped or --json:
  • disable TUI, prompts, spinners, and progress animation
• bounded defaults:
  • limit rows, truncate long fields, and require --full or --verbose for expansion
• stable machine mode:
  • return one documented --json schema per command
• deterministic exit codes:
  • keep success, usage, auth, and runtime failures separated
• mutative safety:
  • require --yes or --force for dangerous actions
  • expose --dry-run for previewable mutations
• explicit errors:
  • always return a Hint: line with the exact next command when recovery is obvious

Enforcement around the CLI

These should be enforced through tests, quality gates, or CI:

• snapshot or schema tests for --json output on agent-consumed commands
• tests proving human output can change without breaking --json
• tests for piped stdout behavior: no TUI, no prompts, no spinner leakage
• tests for bounded default output vs --full
• tests for summary/section/full retrieval flows where the CLI returns rich documents
• tests for doctor --json setup and auth reporting
• tests proving the installed command works from outside the source folder
• tests for discover -> resolve -> read flows using stable IDs
• tests for headless auth failure paths
• tests for deterministic exit codes and Hint: guidance
• help-text checks: grouped commands, examples present, start-here hints where needed
• regression tests for metadata quality:
  • titles
  • summaries
  • tags
  • related links

If drift keeps recurring, add a gate instead of repeating cleanup.

Review checklist

• non-interactive path exists
• --json or --ndjson exists where needed
• TUI has a non-TUI equivalent
• help is grouped and example-rich
• outputs are scoped, sorted, and bounded by default
• summary -> section -> full exists where the CLI exposes large documents or traces
• --json is treated as the stable contract
• doctor --json exists for durable CLIs
• command families are separated into discover, resolve, read, and write where the domain needs them
• short summaries are specific, not generic boilerplate
• tags and adjacent links are useful routing metadata when the CLI returns knowledge-like records
• auth works headlessly or fails clearly
• mutative commands have --dry-run
• confirmations have --yes or --force
• exit codes are deterministic
• errors include exact next steps
• command shape and shorthand usage are consistent
• success output exposes IDs, URLs, durations, and next useful values
• tests enforce the important invariants above

When reviewing an existing CLI

Check:

• discoverability
• examples
• machine-readable output
• doctor/setup surface
• no-TUI behavior
• stdin and pipeline support
• headless auth
• bounded default output
• discover/resolve/read/write separation
• summary/section/full retrieval shape where relevant
• metadata quality for routing
• mutative safety
• deterministic errors
• consistent flags
• semantic output
• idempotency
• tests or gates covering the contract

Companion skill expectations

If the CLI is meant for repeated use across threads, pair it with a companion skill that records:

• when to use the CLI instead of ad hoc shell or browser work
• which command to run first, usually doctor, discover, or summary
• how to keep output bounded
• where file downloads or exports land
• which write commands require explicit user approval

The CLI is the executable surface. The companion skill is the routing memory for future agents.