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Luxferre
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# Bantam: tiny, powerful, DIY AI agent
## About
Bantam is a minimalist, dependency-free AI agent specification and implementation (under 300 SLOC of Python (~250 in the reference implementation)). It provides an agentic loop capable of autonomous tool execution, shell interaction, real-time response streaming, Fibonacci backoff network resilience, and subagent delegation using any OpenAI-compatible completions API.
The entire philosophy of Bantam is built upon two principles:
1. The structure must be as simple as possible for anyone to be able to reimplement the agent from a plain algorithm description.
2. The agent only needs to provide two tools: a tool to call shell commands and a tool to call itself. In theory, this should be sufficient to give LLMs the ability to handle tasks of any complexity.
Because of the second principle, Bantam itself was named after Victorinox Bantam Alox, a small and lightweight Swiss army knife with only two tools.
## Usage
### Prerequisites
- Python 3.7+ (no external dependencies required)
- An OpenAI-compatible API endpoint (or OpenAI API key)
### Running Bantam
1. Configure `model.cfg` with your API settings:
```ini
endpoint=https://api.openai.com/v1
model=gpt-4o
temperature=0.7
api_key=your_api_key_here
stream=true
```
2. Interactive mode:
```bash
python3 bantam.py
```
In interactive mode, prompts can span multiple lines: press **Ctrl+J** to insert a real line break (the cursor moves to the next line), then **Enter** to submit the whole multi-line prompt. This works when `readline` is available; without it, prompts are single-line.
Sessions are saved under `~/.bantam/sessions/` and can be managed with these commands:
- `/save` — save the entire conversation to a new session file (auto-id like `20260808-190038`) and generate its summary
- `/list` — list saved sessions (newest first) with their ids, timestamps, message counts and summaries
- `/load <id>` — load a saved session (exact id or unique prefix) and continue from there
- `/compact` — summarize the conversation with the LLM and compact the context down to just the system message plus the summary
- `/help` — show all supported commands
- `/clear` — reset the conversation to just the system prompt
- `/quit` — exit
The current conversation is also **auto-saved** to `~/.bantam/sessions/autosave.json` after every turn, on `/clear`, `/load`, `/compact`, and on exit — so you can always `/load autosave` to resume where you left off.
3. File input mode:
```bash
python3 bantam.py prompt.txt
```
## Rules of Bantam (The Algorithm)
Using these rules, everyone can build their own copy of Bantam from scratch in little time in any language that supports file access, shell and HTTP(S) calls.
### High-Level Overview
1. **Initialization**: Read `system.txt` and `model.cfg`. Prepare an array of messages starting with the system prompt `{"role": "system", "content": system_prompt}`.
2. **Input Processing**: Take user prompt (via command-line file parameter or interactive stdin), append `{"role": "user", "content": prompt}`, and invoke `AL(cfg, messages)`.
3. **Agentic Loop (`AL`)**:
- Send `messages` and tool definitions to the OpenAI-compatible `/chat/completions` API endpoint with custom `User-Agent` headers.
- On network or HTTP failure, retry using Fibonacci backoff delays (`1s, 1s, 2s, 3s, 5s`).
- If `stream=true`, parse SSE data chunks (`data: {...}`) in real-time to stream reasoning content (`reasoning_content`) and response text directly to stdout, bracketing the reasoning block with `--- reasoning start ---` / `--- reasoning end ---` markers.
- Reconstruct the assistant message. If `tool_calls` exist, trace the call (`[tool call: name(args)]`), validate JSON arguments, execute the requested tool (`shell_exec` or `run_subagent`), trace the result (`[tool result: name]`), append the tool response `{"role": "tool", "tool_call_id": id, "content": result}`, and repeat the loop.
- If no tool calls remain or `max_al_iterations` is reached, return the updated messages list.
---
### Main program
1. Read system prompt from `system.txt` (default if missing).
2. Read model parameters from `model.cfg` (`key=value` format).
3. Prepare a new message list with the system prompt (`role: "system"`).
4. Read the first command-line parameter. If non-empty, read user prompt from the specified file, append to `messages` (`role: "user"`), run `AL(cfg, messages)`, and exit.
5. Read user prompt from standard input (with `readline` line editing and history in `~/.bantam_history`; **Ctrl+J** inserts a real newline into the line being edited). If equal to `/quit` or EOF, exit. If equal to `/clear`, reset `messages` to step 3 and return to step 5. If equal to `/save`, write the whole `messages` array to `~/.bantam/sessions/<id>.json` (with an auto-generated summary) and return to step 5. If equal to `/list`, print saved sessions and their summaries and return to step 5. If starting with `/load`, replace `messages` with the saved session's messages (by exact id or unique prefix) and return to step 5. If equal to `/compact`, ask the LLM to summarize the conversation, replace `messages` with `[system, summary-user-message]`, and return to step 5. If equal to `/help`, print the command list and return to step 5. After every user turn and on exit, auto-save `messages` to `~/.bantam/sessions/autosave.json`.
6. Append user prompt to `messages` (`role: "user"`), run `AL(cfg, messages)`, and go to step 5.
### Agentic loop (`AL(cfg, messages)`) function
1. Call OpenAI-compatible Completions API (`POST {endpoint}/chat/completions`) using parameters from `cfg` (`model`, `temperature`, optional `api_key` bearer header).
- Set custom `User-Agent` header (`Mozilla/5.0 (compatible; Bantam/1.0)`) to avoid gateway 403 blocks.
- Retry network/HTTP errors with Fibonacci backoff delays (`1s, 1s, 2s, 3s, 5s`).
- If `stream=true`, parse SSE stream (`data: {...}`) for real-time reasoning and text output, bracketing reasoning with `--- reasoning start ---` / `--- reasoning end ---` markers.
2. Append the assistant's response message object to `messages`. If non-streaming and response has reasoning tokens (`reasoning_content` or `reasoning`), output them wrapped in `--- reasoning start ---` / `--- reasoning end ---` markers.
3. If there are pending `tool_calls` in the assistant response:
- For each tool call, output a trace log (`[tool call: name(args)]`).
- Validate JSON arguments. If invalid, format a tool-error response so the LLM can self-correct.
- Execute tool action (`shell_exec` or `run_subagent`).
- Output a trace log of the result (`[tool result: name]`).
- Append tool result message (`role: "tool"`, `tool_call_id`, `content`: result string) to `messages`.
- Loop back to step 1.
4. If no pending tool calls (or if `max_al_iterations` is reached), stop and return `messages`.
### Model configuration parameters
- `endpoint` (base OpenAI-compatible API URL, default `https://api.openai.com/v1`)
- `model` (model name, e.g. `gpt-4o`)
- `temperature` (model temperature, default 0.7)
- `api_key` (API key / Bearer token, optional; fall back to `OPENAI_API_KEY` env var)
- `stream` (stream response tokens in real-time, default `true`)
- `color` (ANSI coloring: `auto` (TTY-detected, default), `always`, or `never`; also disabled by `NO_COLOR`/`BANTAM_NO_COLOR` env vars)
- `timeout` (HTTP timeout in seconds for LLM API calls, default 60)
- `shell_timeout` (timeout in seconds for `shell_exec` commands, default 120)
- `max_al_iterations` (max tool-call loop iterations per `AL()` invocation, default 1000)
When enabled, the interactive console uses a subtle ANSI palette: the pending-request status `...requesting...` is darkened bold, reasoning markers are cyan, reasoning text is dim, `[tool call: ...]` traces are yellow, `[tool result: ...]` headers are green, tool result bodies are dim (red for tool errors/unknown tools), and errors/network retries are red. Tool result payloads fed back to the LLM are never colored.
### Tool call definitions
#### `run_subagent` tool
- Parameters: `prompt` (string)
- Return value: string
- Action: run `AL(cfg, [{"role": "system", "content": system_prompt + "\n\nImportant: this is a child agent"}, {"role": "user", "content": prompt}])` and return the text content of the last `assistant`-role message.
#### `shell_exec` tool
- Parameters: `command` (string)
- Return value: string
- Action: run shell command specified in `command` subject to `shell_timeout` (default 120s) and return `output + '\n\nexit: ' + exit_code` string.
## FAQ
### Why no MCP support?
If you need MCP server tools, there's nothing a simple shell wrapper cannot solve in this case.
### Why no sandboxing?
Same philosophy as the Pi agent: there's nothing a simple chroot environment cannot solve in case sandboxing is really necessary.
### Any advanced authentication schemes or header injection?
You can pair Bantam with the [Dynagate](https://code.luxferre.top/luxferre/dynagate) LLM gateway to achieve all that.
## Credits
Created by Luxferre in 2026, released into the public domain with no warranties.
Executable
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#!/usr/bin/env python3
# Bantam agent, tiny, powerful, DIY. Public domain. Created by Luxferre in 2026.
import sys, os, json, time, subprocess, urllib.request
try: import readline
except ImportError: readline = None
HIST = os.path.expanduser("~/.bantam_history")
SDIR = os.path.expanduser("~/.bantam/sessions")
AUTO = os.path.join(SDIR, "autosave.json")
_COL = False
def c(t, *cs): return t if not _COL or not cs else "\033[" + ";".join(map(str, cs)) + "m" + t + "\033[0m"
def col(cfg):
if os.environ.get("NO_COLOR") or os.environ.get("BANTAM_NO_COLOR"): return False
m = str(cfg.get("color", "auto")).strip().lower()
if m == "always": return True
if m == "never": return False
try: return sys.stdout.isatty()
except Exception: return False
def get_cfg(path="model.cfg"):
d = {"endpoint": "https://opencode.ai/zen/v1", "model": "deepseek-v4-flash-free", "temperature": "0.7", "api_key": "-", "timeout": "60", "shell_timeout": "120", "max_al_iterations": "1000", "stream": "true", "color": "auto"}
if os.path.exists(path):
for ln in open(path, encoding="utf-8"):
ln = ln.strip()
if ln and not ln.startswith("#") and "=" in ln:
k, v = ln.split("=", 1); d[k.strip()] = v.strip()
if not d.get("api_key") and "OPENAI_API_KEY" in os.environ: d["api_key"] = os.environ["OPENAI_API_KEY"]
return d
def num(cfg, k, d):
try: return type(d)(cfg.get(k, d))
except (TypeError, ValueError): return d
def prompt(path="system.txt"):
if os.path.exists(path): return open(path, encoding="utf-8").read().strip()
return "You are Bantam, a tiny, powerful AI agent."
def T(name, desc, props): return {"type": "function", "function": {"name": name, "description": desc, "parameters": {"type": "object", "properties": props, "required": list(props)}}}
TOOLS = [T("shell_exec", "Run a shell command, return output and exit code.", {"command": {"type": "string"}}),
T("run_subagent", "Run a child agent with a prompt.", {"prompt": {"type": "string"}})]
def shell(cmd, t=120):
try:
r = subprocess.run(cmd, shell=True, capture_output=True, text=True, timeout=float(t))
return f"{(r.stdout + r.stderr).strip()}\n\nexit: {r.returncode}"
except subprocess.TimeoutExpired as e:
out, err = e.stdout or "", e.stderr or ""
if isinstance(out, bytes): out = out.decode("utf-8", "replace")
if isinstance(err, bytes): err = err.decode("utf-8", "replace")
return f"{(out + err).strip()}\n\n[shell timeout after {t}s]\nexit: -1"
fib = [1, 1, 2, 3, 5, 8, 13, 21, 34]
def llm(cfg, msgs, tools):
url = cfg["endpoint"].rstrip("/") + "/chat/completions"
h = {"Content-Type": "application/json", "User-Agent": "Mozilla/5.0 (compatible; Bantam/1.0)"}
k = cfg.get("api_key", "").strip()
if k and k != "-": h["Authorization"] = "Bearer " + k
st = cfg.get("stream", "true").lower() in ("true", "1", "yes")
p = {"model": cfg["model"], "temperature": float(cfg.get("temperature", 0.7)), "messages": msgs, "stream": st}
if tools: p["tools"] = tools
pend = c("...requesting...", 1, 2)
for i, dly in enumerate(fib + [0]):
try:
if _COL: sys.stdout.write("\r" + pend); sys.stdout.flush()
else: sys.stdout.write(pend + "\n"); sys.stdout.flush()
req = urllib.request.Request(url, data=json.dumps(p).encode(), headers=h, method="POST")
with urllib.request.urlopen(req, timeout=num(cfg, "timeout", 60)) as r:
if not st:
msg = json.loads(r.read().decode())["choices"][0]["message"]
if _COL: sys.stdout.write("\r\033[K"); sys.stdout.flush()
return msg
if _COL: sys.stdout.write("\r\033[K"); sys.stdout.flush()
content, reas, tcs, rh, ch = "", "", {}, False, False
for ln in r:
ln = ln.decode("utf-8").strip()
if not ln.startswith("data:"): continue
if ln[5:].strip() == "[DONE]": break
try:
dl = json.loads(ln[5:].strip())["choices"][0].get("delta", {})
rc = dl.get("reasoning_content") or dl.get("reasoning")
if rc:
if not rh: sys.stdout.write(c("--- reasoning start ---", 36) + "\n"); rh = True
sys.stdout.write(c(rc, 2)); sys.stdout.flush(); reas += rc
cc = dl.get("content")
if cc:
if rh and not ch: sys.stdout.write("\n" + c("--- reasoning end ---", 36) + "\n\n")
ch = True; sys.stdout.write(cc); sys.stdout.flush(); content += cc
for tc in dl.get("tool_calls", []):
ti = tc.get("index", 0)
if ti not in tcs: tcs[ti] = {"id": tc.get("id", ""), "type": "function", "function": {"name": "", "arguments": ""}}
if tc.get("id"): tcs[ti]["id"] = tc["id"]
fn = tc.get("function")
if fn:
if fn.get("name"): tcs[ti]["function"]["name"] += fn["name"]
if fn.get("arguments"): tcs[ti]["function"]["arguments"] += fn["arguments"]
except Exception: pass
if rh and not ch: sys.stdout.write("\n" + c("--- reasoning end ---", 36) + "\n")
elif ch: sys.stdout.write("\n")
sys.stdout.flush()
m = {"role": "assistant", "content": content or None}
if reas: m["reasoning_content"] = reas
if tcs: m["tool_calls"] = list(tcs.values())
return m
except Exception as e:
if _COL: sys.stdout.write("\r\033[K"); sys.stdout.flush()
if i < len(fib): print(c(f"[network error: {e}, retrying in {dly}s...]", 31)); time.sleep(dly)
else: raise
MAX_DEPTH = 5
def AL(cfg, msgs, sp, depth=0):
stime, mx, st = num(cfg, "shell_timeout", 120), num(cfg, "max_al_iterations", 1000), cfg.get("stream", "true").lower() in ("true", "1", "yes")
for _ in range(mx):
m = llm(cfg, msgs, TOOLS); msgs.append(m)
if not st:
reas = m.get("reasoning_content") or m.get("reasoning")
if reas: print(c("--- reasoning start ---", 36) + "\n" + c(reas, 2) + "\n" + c("--- reasoning end ---", 36) + "\n")
if m.get("content"): print(m["content"])
tcs = m.get("tool_calls")
if not tcs: break
for tc in tcs:
fn, astr = tc["function"]["name"], tc["function"].get("arguments", "{}")
print(c(f"[tool call: {fn}({astr})]", 33))
try:
a = json.loads(astr) if astr else {}
if not isinstance(a, dict): raise ValueError("args must be a JSON object")
err = ""
except Exception as e: err, a = str(e), {}
if err: res, sty = f"[tool error: invalid JSON args for {fn}: {err}. Raw: {astr!r}]", 31
elif fn == "shell_exec": res, sty = shell(a.get("command", ""), stime), 2
elif fn == "run_subagent":
if depth >= MAX_DEPTH:
res, sty = f"[subagent depth limit ({MAX_DEPTH}) reached, child not spawned]", 31
else:
sub = [{"role": "system", "content": sp + "\n\nImportant: this is a child agent"}, {"role": "user", "content": a.get("prompt", "")}]
res, sty = last(AL(cfg, sub, sp, depth + 1)), 2
else: res, sty = f"Unknown tool: {fn}", 31
print(c(f"[tool result: {fn}]", 32) + "\n" + c(res, sty) + "\n")
msgs.append({"role": "tool", "tool_call_id": tc["id"], "content": res})
else: msgs.append({"role": "assistant", "content": f"[max AL iterations ({mx}) reached]"})
return msgs
def last(msgs):
for m in reversed(msgs):
if m.get("role") == "assistant" and m.get("content"): return m["content"]
return ""
def sdir(): os.makedirs(SDIR, exist_ok=True); return SDIR
def summary(msgs):
for m in msgs:
if m.get("role") == "user" and isinstance(m.get("content"), str) and m["content"].strip():
t = " ".join(m["content"].split()); return t[:80] + ("..." if len(t) > 80 else "")
return "(empty session)"
def save(msgs):
d, base, i = sdir(), time.strftime("%Y%m%d-%H%M%S"), 1
sid, path = base, os.path.join(d, base + ".json")
while os.path.exists(path): i += 1; sid = base + "-" + str(i); path = os.path.join(d, sid + ".json")
data = {"id": sid, "created": time.strftime("%Y-%m-%d %H:%M:%S"), "summary": summary(msgs), "messages": msgs}
open(path, "w", encoding="utf-8").write(json.dumps(data, ensure_ascii=False, indent=2))
return sid, data["summary"]
def sessions():
out = []
if os.path.isdir(SDIR):
for fn in os.listdir(SDIR):
if not fn.endswith(".json"): continue
try:
d = json.load(open(os.path.join(SDIR, fn), encoding="utf-8"))
out.append((d.get("id", fn[:-5]), d.get("created", ""), d.get("summary", ""), len(d.get("messages", []))))
except Exception: pass
return sorted(out, key=lambda x: x[0], reverse=True)
def load(sid):
entries = []
if os.path.isdir(SDIR):
for fn in os.listdir(SDIR):
if not fn.endswith(".json"): continue
try: entries.append((json.load(open(os.path.join(SDIR, fn), encoding="utf-8")).get("id", fn[:-5]), os.path.join(SDIR, fn)))
except Exception: pass
hit = next((e for e in entries if e[0] == sid), None)
if not hit:
pref = [e for e in entries if e[0].startswith(sid)]
if len(pref) == 1: hit = pref[0]
elif len(pref) > 1: raise KeyError("ambiguous prefix: " + ", ".join(e[0] for e in pref))
if not hit: raise KeyError(sid)
return json.load(open(hit[1], encoding="utf-8"))["messages"]
def autosave(msgs):
d = {"id": "autosave", "created": time.strftime("%Y-%m-%d %H:%M:%S"), "summary": summary(msgs), "messages": msgs}
open(os.path.join(sdir(), "autosave.json"), "w", encoding="utf-8").write(json.dumps(d, ensure_ascii=False, indent=2))
def summarize(cfg, msgs):
conv = []
for m in msgs:
if m.get("role") == "system": continue
ct = m.get("content")
if not ct and m.get("tool_calls"): ct = json.dumps([{"function": tc["function"]["name"], "arguments": tc["function"]["arguments"]} for tc in m["tool_calls"]], ensure_ascii=False)
if not ct: continue
if len(ct) > 4000: ct = ct[:4000] + "...[truncated]"
conv.append(f"{m.get('role', '?')}: {ct}")
if not conv: return "", "no conversation to summarize"
joined = "\n\n".join(conv)
if len(joined) > 100000: joined = joined[-100000:] + "\n...[earlier parts truncated]"
sm = [{"role": "system", "content": "You are a conversation summarizer for an AI agent's context window. Summarize concisely but completely, preserving all important facts, decisions, code, errors, and the current task state, so the agent can continue the work without the original messages. Output only the summary."},
{"role": "user", "content": "Summarize this conversation:\n\n" + joined}]
cc = dict(cfg); cc["stream"] = "false"
try: m = llm(cc, sm, [])
except Exception as e: return "", f"LLM error: {e}"
s = (m.get("content") or m.get("reasoning_content") or "").strip()
return (s, None) if s else ("", "LLM returned an empty summary")
def compact(cfg, msgs):
if not msgs or msgs[0].get("role") != "system": return msgs, "", "session has no system message"
s, err = summarize(cfg, msgs)
if err: return msgs, "", err
return [{"role": "system", "content": msgs[0]["content"]}, {"role": "user", "content": "Summary of the previous conversation:\n" + s + "\n\nPlease continue from here."}], s, None
def main():
global _COL
if readline:
try: readline.read_history_file(HIST)
except OSError: pass
try: readline.parse_and_bind('"\\C-j": "\\C-v\\C-j"') # real LF via quoted-insert
except Exception: pass
sp, cfg = prompt(), get_cfg()
_COL = col(cfg)
msgs = [{"role": "system", "content": sp}]
if len(sys.argv) > 1 and sys.argv[1]:
p = sys.argv[1]
if not os.path.exists(p): print(c(f"Error: file '{p}' not found.", 31)); sys.exit(1)
msgs.append({"role": "user", "content": open(p, encoding="utf-8").read().strip()})
AL(cfg, msgs, sp); autosave(msgs)
if readline:
try: readline.write_history_file(HIST)
except OSError: pass
sys.exit(0)
print(c("Bantam Agent ready", 1, 32) + c(" (Ctrl+J = new line)", 2))
while True:
try: u = input(c("> ", 1, 36)).strip()
except (EOFError, KeyboardInterrupt): print(); break
if not u: continue
if u == "/quit": break
elif u == "/clear": msgs = [{"role": "system", "content": sp}]; autosave(msgs); continue
elif u == "/save":
sid, sm = save(msgs); print(c(f"[session saved: {sid}]", 32) + " " + c(sm, 2)); continue
elif u == "/list":
ss = sessions()
if not ss: print(c("No sessions saved yet.", 33)); continue
for sid, st, sm, n in ss:
mk = c(" (autosave)", 33) if sid == "autosave" else ""
print(c(sid, 32) + mk + c(f" {st} [{n} msgs]", 2) + "\n " + c(sm, 2))
continue
elif u.startswith("/load"):
parts = u.split(None, 1)
if len(parts) < 2: print(c("Usage: /load <session-id>", 31)); continue
try:
msgs = load(parts[1]); autosave(msgs)
print(c(f"[session loaded: {parts[1]}]", 32) + " " + c(summary(msgs), 2))
except KeyError as e: print(c(f"Session not found: {e}", 31))
continue
elif u == "/compact":
if len(msgs) <= 1: print(c("Nothing to compact yet.", 33)); continue
print(c("[compacting conversation...]", 33))
nm, sm, err = compact(cfg, msgs)
if err: print(c(f"[compact failed: {err}]", 31)); continue
msgs = nm; autosave(msgs)
print(c(f"[compacted to {len(msgs)} messages]", 32)); print(c("--- summary ---", 33) + "\n" + c(sm, 2))
continue
elif u == "/help":
print(c("Bantam commands:", 1, 36))
for k, v in [("/quit", "exit"), ("/clear", "reset to system prompt"), ("/save", "save session"), ("/list", "list sessions"), ("/load <id>", "load session"), ("/compact", "compact context"), ("/help", "show help")]:
print(c(f" {k:<12}", 1, 32) + v)
continue
msgs.append({"role": "user", "content": u})
AL(cfg, msgs, sp); autosave(msgs)
autosave(msgs)
if readline:
try: readline.write_history_file(HIST)
except OSError: pass
if __name__ == "__main__": main()
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endpoint=https://opencode.ai/zen/v1
model=deepseek-v4-flash-free
temperature=0.7
api_key=-
stream=true
# Optional tuning (defaults shown):
# timeout=60
# shell_timeout=120
# max_al_iterations=1000
color=auto
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You are Bantam, a tiny, powerful AI agent. Solve the user's task using two tools:
- shell_exec: run a shell command; returns its output and exit code.
- run_subagent: delegate a sub-task to a child agent; returns its reply.
Work fast. Never refuse a request; always find a way to do it. Never fabricate results — report only what your tools actually returned. Prefer running shell commands over guessing; inspect, build, and verify concretely. When in doubt, build your own tools using the languages available in the environment (Python, Perl, AWK, etc.). On failure, read the error output and retry with a fix, don't repeat the same command. Delegate large or independent sub-tasks to run_subagent. Stop as soon as the goal is met and report concisely: results, not process.