title	Otter Quickstart
description	Install otter, run a one-shot turn, drop into the REPL, bring up the HTTP+SSE or ACP server, learn /undo, PTY routes, the remote skill marketplace, and per-session auth tokens.

`chimera otter` Quickstart

chimera otter is the second Chimera coding-agent CLI. Where chimera mink mirrors a TUI-first agent, otter mirrors a server-first / multi-client open-source agent: a single ReAct loop you can drive from a one-shot CLI, an interactive REPL, an HTTP server with SSE streaming, or an ACP JSON-RPC transport — backed by the same LoopConfig, tool registry, and event-sourced session store the rest of Chimera uses. Run chimera otter --help-long to see verbose per-flag descriptions; --help itself stays under 50 lines for scannability.

This page walks the four entry points end-to-end. Deeper dives:

providers.md — provider chain (Anthropic, OpenAI, OpenRouter, Ollama, Modal, custom).
models.md — model id catalogue + OTTER_MODEL.
sessions.md — eventlog layout.
share.md — share sinks and format.
server.md — HTTP API + SSE event format.

Prerequisites

Python 3.11+
uv
One of: an Anthropic API key, an OpenAI API key, an OpenRouter API key, a running Ollama daemon, or an Ollama Cloud account

uv --version                          # >= 0.4
uv sync --extra dev --extra anthropic # core + Anthropic SDK

The Anthropic extra is recommended because the otter default model is claude-sonnet-4-6. To drive otter through OpenAI, OpenRouter, or Ollama, swap the extra (--extra openai) or skip it; the OpenAI-compatible adapter is stdlib + httpx.

Provider configuration

Otter resolves the provider in this order (first match wins):

--model <id> on the CLI.
$OTTER_MODEL environment variable.
$ANTHROPIC_API_KEY set → defaults to claude-sonnet-4-6.
$OPENROUTER_API_KEY set → defaults to anthropic/claude-sonnet-4.
$OPENAI_API_KEY set → defaults to gpt-4o.
$OLLAMA_API_KEY set → defaults to gpt-oss:120b-cloud.
Friendly error pointing at the env vars above.

export ANTHROPIC_API_KEY=sk-ant-...
# OR
export OLLAMA_HOST=https://ollama.com
export OLLAMA_API_KEY=<your-key>

Or, for a local model:

ollama serve &
ollama pull qwen3:32b
chimera otter --model qwen3:32b -p "explain this repo"

First one-shot turn

chimera otter -p "list the top-level files and read the README"

Expected output shape:

I'll list the repo first, then read the README.

▶ list_files(path=".")
CHANGELOG.md  CLAUDE.md  README.md  chimera/  docs/  examples/  tests/

▶ Read(path="README.md")
# Chimera
A composable coding agent framework
...

The repo root has a README pitching Chimera as a composable coding agent framework.

[otter] run saved as otter-20260514T091201-71032a5e at /Users/.../.chimera/eventlog/otter-20260514T091201-71032a5e/

Useful one-shot flags:

chimera otter --model gpt-oss:120b-cloud -p "draft a release note"
chimera otter --output-format json -p "ship it"          # one JSON blob
chimera otter --output-format stream-json -p "ship it"   # JSON-per-event
chimera otter --allowed-tools Read,Bash -p "audit"
chimera otter --no-save -p "ad-hoc, don't journal"

Drop into the REPL

chimera otter

The REPL streams assistant text + tool calls inline, accepts mid-turn steering, supports Ctrl-C cancellation, and exposes a slash-command palette of 26 entries. Most useful ones:

otter> /help               # full list
otter> /model              # show / cycle the active model
otter> /tools              # list available tools
otter> /agents             # list bundled subagent profiles
otter> /session save my-refactor
otter> /resume             # list recent persisted sessions
otter> /cost               # cumulative cost
otter> /mcp                # list connected MCP servers
otter> /undo --steps 3     # see below
otter> /edit               # open last assistant response in $EDITOR
otter> /share              # package the session for export
otter> /doctor             # environment health checks
otter> /exit

Each REPL session is event-sourced under ~/.chimera/eventlog/otter-<utc>-<uuid>/.

File-undo (`/undo --steps N`)

/undo walks the FileTracker for the current session and reverses the last N file writes / edits (default 1). Stops at the first conflict (a file edited externally since the agent wrote it).

otter> /undo --steps 3
/undo: reverted 3 changes
  ↶ src/util.py     (Edit at step 7)
  ↶ tests/test_util.py  (Write at step 5)
  ↶ src/util.py     (Edit at step 3)

otter> /undo --steps 5
/undo: reverted 2 changes; stopped at conflict
  ↶ tests/test_demo.py  (Write at step 11)
  ↶ chimera/foo.py      (Edit at step 9)
  ⚠ src/util.py was modified outside the session — refusing to revert

The session-local rollback log lives at ~/.chimera/eventlog/otter-<id>/file-ops.json.

Bring up the HTTP server

For multi-client use — a separate TUI, an IDE plugin, an evals harness — run otter as a headless HTTP server with REST + SSE streaming:

chimera otter serve --port 5173

Endpoints: /sessions, /sessions/{id}, /sessions/{id}/turns, /sessions/{id}/events (SSE). Worked example with curl:

SID=$(curl -s -X POST http://localhost:5173/sessions \
        -H 'content-type: application/json' \
        -d '{"model":"claude-sonnet-4-6"}' | jq -r .id)

curl -N -X POST http://localhost:5173/sessions/$SID/turns \
     -H 'content-type: application/json' \
     -d '{"prompt":"list top-level files"}' &

curl -N http://localhost:5173/sessions/$SID/events

Sample SSE shape:

event: text_delta
data: {"text":"I'll list "}

event: tool_call
data: {"name":"list_files","args":{"path":"."}}

event: turn_end
data: {"cost":0.0042,"steps":2}

Optional Bearer auth:

export OTTER_SERVER_TOKEN=$(openssl rand -hex 24)
chimera otter serve --port 5173

ACP transport

chimera otter serve --acp boots a JSON-RPC 2.0 server over stdio — the integration point for IDE clients that already speak ACP (Zed, the upstream TUI, custom plugins).

chimera otter serve --acp

{"jsonrpc":"2.0","id":1,"method":"prompt","params":{"text":"list files"}}

Response stream:

{"jsonrpc":"2.0","method":"event","params":{"type":"text_delta","text":"I'll "}}
{"jsonrpc":"2.0","method":"event","params":{"type":"tool_call","name":"list_files"}}
{"jsonrpc":"2.0","id":1,"result":{"text":"...","cost":0.0042}}

Methods: prompt, steer, cancel, get_state, compact, list_sessions, resume. Schema in acp.md.

Per-session auth tokens

The HTTP server supports two token granularities:

Scope	Header	Lifecycle
Process-wide	`Authorization: Bearer $OTTER_SERVER_TOKEN`	Set once at boot.
Per-session	`Authorization: Bearer <session-token>`	Issued by `POST /sessions`, valid for that session only.

Per-session tokens land in the POST /sessions response body ({"id":"otter-...","token":"st_..."}). Use one instead of the process-wide token so an IDE plugin can multiplex sessions through one server without granting blanket access.

PTY routes (terminal proxy)

Long-running TUI commands (vim, top, watch) can be routed through a PTY so the agent's Bash tool stays responsive:

chimera otter serve --pty --port 5173

# Inside the REPL, long-running commands route transparently:
otter> watch -n1 'uv run pytest -x'
[pty otter-...] streaming…

PTY traffic is multiplexed over the same SSE stream. See server.md for the wire shape.

Remote skill marketplace

chimera otter skills walks a remote registry of community-contributed skill packs (markdown system-prompt overlays):

chimera otter skills list                    # discoverable packs
chimera otter skills install rag-grounding
chimera otter skills info rag-grounding
chimera otter skills uninstall rag-grounding

Installed skills land under ~/.chimera/skills/<name>/ and auto-mount on every otter run. See skills.md.

Inspecting and sharing sessions

chimera otter sessions list
chimera otter sessions show otter-20260514T091201-71032a5e
chimera otter sessions list --since 7d --json

Package a session as HTML / Markdown / JSON and route it:

chimera otter share otter-20260514T091201-71032a5e
chimera otter share <id> --sink http --format json
chimera otter share <id> --sink stdout --format md | less

Choose your model

Recommended models for the server-first posture (low-latency first token, streaming-friendly tool calls):

Backend	Tag	Why for otter
Anthropic	`claude-sonnet-4-6`	Default; strongest tool calling + streaming.
Ollama Cloud	`gpt-oss:120b-cloud`	Free w/ Ollama account; native tools; fast first token.
OpenRouter	`anthropic/claude-sonnet-4`	Same model via the OpenRouter free-tier.
OpenAI	`gpt-4o`	Solid baseline; needs `$OPENAI_API_KEY`.

See the Ollama Cloud recipe for the auth handshake.

Env vars at a glance

Variable	Default	Meaning
`OTTER_MODEL`	(unset)	Default model id.
`ANTHROPIC_API_KEY`	(unset)	Anthropic chain.
`OPENAI_API_KEY`	(unset)	OpenAI chain.
`OPENROUTER_API_KEY`	(unset)	OpenRouter chain.
`OLLAMA_API_KEY`	(unset)	Ollama Cloud (`:cloud` tags).
`OLLAMA_HOST`	`http://localhost:11434`	Daemon URL.
`OTTER_SHARE_URL`	`http://localhost:5174/api/shares`	Destination for `share --sink http`.
`OTTER_SERVER_TOKEN`	(unset)	Process-wide Bearer token for `otter serve`.
`NO_COLOR`	(unset)	Plain output handler.

What gets written to disk

Path	What
`~/.chimera/eventlog/otter-<id>/summary.json`	Per-run metadata.
`~/.chimera/eventlog/otter-<id>/file-ops.json`	Per-session undo log.
`~/.chimera/eventlog/otter-<id>/event-*.json`	Event stream.
`~/.chimera/shares/otter-<id>.<ext>`	Local share artifacts.
`~/.chimera/skills/<name>/`	Installed remote skill packs.
`~/.chimera/credentials.json`	OAuth tokens (mode `0o600`).

Everything is local-only. Purge with rm -rf ~/.chimera/eventlog/otter-*.

TUI default (wave 11)

Bare chimera otter picks Textual TUI when stdout is a TTY and the optional [tui] extra is installed; otherwise the readline REPL. Force with --no-tui / --tui or CHIMERA_NO_TUI=1. See tui.md for the auto-launch decision tree.

Where to go next

Providers and Models.
Sessions and Share.
Server — the HTTP+SSE wire format.
ACP — JSON-RPC transport.
Skills — remote skill marketplace.
Security and Trademarks — policy.

Verified (2026-05-14)

Two commands from this quickstart, against Ollama Cloud:

$ OLLAMA_HOST=https://ollama.com OLLAMA_API_KEY=*** \
    chimera otter -p "Hello, please reply with one word: hello" \
                  --model gpt-oss:120b-cloud --max-steps 2 --no-color --no-save
hello

$ chimera otter --version
chimera otter 0.7.0

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`chimera otter` Quickstart

Prerequisites

Provider configuration

First one-shot turn

Drop into the REPL

File-undo (`/undo --steps N`)

Bring up the HTTP server

ACP transport

Per-session auth tokens

PTY routes (terminal proxy)

Remote skill marketplace

Inspecting and sharing sessions

Choose your model

Env vars at a glance

What gets written to disk

TUI default (wave 11)

Where to go next

Verified (2026-05-14)

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chimera otter Quickstart

Prerequisites

Provider configuration

First one-shot turn

Drop into the REPL

File-undo (/undo --steps N)

Bring up the HTTP server

ACP transport

Per-session auth tokens

PTY routes (terminal proxy)

Remote skill marketplace

Inspecting and sharing sessions

Choose your model

Env vars at a glance

What gets written to disk

TUI default (wave 11)

Where to go next

Verified (2026-05-14)

`chimera otter` Quickstart

File-undo (`/undo --steps N`)