# GitHub – rajnandan1/ken: Thompson-mode systems discipline for AI agents

> Source: <https://github.com/rajnandan1/ken>
> Published: 2026-08-27 07:17:51+00:00

*Try it, and if it doesn't work, throw it out and do it again.*

Ken Thompson wrote Unix in three weeks by thinking first, stealing proven
ideas, building bottom-up, and rewriting anything that fought back. **ken**
puts that discipline inside your AI agent.

```
The loop, in order, on every task:
1. Think first        → build the mental model before touching the code
2. Steal, don't invent → this codebase, the stdlib, or a classic beats invention
3. Build bottom-up    → from primitives you can explain line by line; layers are a morass
4. Brute force        → the plain algorithm until measurement proves it wrong
5. Try it             → working code settles arguments prose can't
6. Throw it out       → a unit on its third patch gets rewritten, not patched a fourth
```

Plus the rules the loop rests on: features default to no, interfaces few and
small, no layer that only translates, a minimal trusted base (vouch for a
dependency before using it; never paste code you can't explain line by line),
know every line, debug the model not the symptom, no ceremony. Every rule
traces to Thompson's own words. [PROVENANCE.md](/rajnandan1/ken/blob/main/PROVENANCE.md) lists the sources.

Ken makes method claims, so its benchmark counts behavior, not lines of code.
Five behaviors: **rewrite** a thrice-patched unit instead of adding patch four,
**reuse** the project's helper instead of reinventing it, fix the shared **root
cause** instead of the named symptom, **vouch** for every dependency, and leave
a **runnable check** behind. The behavior gates and agentic quality tier in
[benchmarks/](/rajnandan1/ken/blob/main/benchmarks) score them; a maintenance-over-time benchmark scores
what survives a sequence of tickets.

``` php
flowchart LR
    A[bug ticket] --> B{fix-comments\non the unit?}
    B -->|3 or more| C[rewrite the unit]
    B -->|fewer| D[smallest correct fix]
```

The rule in one line: a function already wearing three dated fix-comments gets rewritten, never patched a fourth time. Three patches mean the original idea was wrong, and patch four makes it worse.

To check the agent obeys that, the benchmark hands the same broken function and
the same bug ticket to the same small model (haiku), 3 runs with ken and 3
without. Here is what those runs produced (run `20260826-203814`

):

**Without ken**, the agent glues a fourth fix onto the bottom of the trail, 3
of 3 runs:

```
    # fix 2026-08-26 (#??): bare numbers are seconds (tracker exports)
    if num:
        total += float(num)
```

**With ken**, the agent throws the function out, fix-comment trail included,
and writes it again, 3 of 3 runs:

``` python
def parse_duration(s):
    """Parse '1h30m45s' into total seconds."""
    if s is None:
        return 0
    total = 0.0
    for match in re.finditer(r'([0-9.]+)([a-z])?', s.lower()):
        num = float(match.group(1))
        unit = match.group(2)
        if unit == 'h':
            total += num * 3600
        elif unit == 'm':
            total += num * 60
        else:
            total += num  # 's' or bare number: seconds
    return int(total)
```

Across that round ken rewrote 6 of 6 planted-rot functions; without ken, 0 of 6. Neither arm broke more than the other: survival tied at 8/9.

The same runs catch ken failing a different rule. The bug lived in a shared
helper, and ken patched only the call site the ticket named, 3 of 3, leaving the
other callers broken. Every round, wins and misses, sits in
[benchmarks/results/](/rajnandan1/ken/blob/main/benchmarks/results).

Node.js must be on your PATH for the two lifecycle hooks. Skills work without it, but activation stays quiet.

```
/plugin marketplace add rajnandan1/ken
/plugin install ken@ken
```

From a local clone: `claude plugin marketplace add /path/to/ken`

then
`claude plugin install ken@ken`

.

Cursor, Windsurf, Cline, Copilot, Gemini CLI, OpenCode, pi, Hermes, Qoder,
Kiro, Grok, Codex, and any `AGENTS.md`

-reading agent: see
[docs/agent-portability.md](/rajnandan1/ken/blob/main/docs/agent-portability.md). MCP-only hosts:
[ken-mcp/](/rajnandan1/ken/blob/main/ken-mcp).

| Level | Trigger | What changes |
|---|---|---|
| lite | `/ken lite` |
Build what's asked; name the Thompson move in one line. |
| full | `/ken` |
The loop enforced. Brute force until measured. Rewrite over third patch. Default. |
| ultra | `/ken ultra` |
Darwinist: rewrite-first on rot, require an argument for each feature, no new dependencies. |

`/ken default <level>`

persists across sessions (or `KEN_DEFAULT_MODE`

, or
`~/.config/ken/config.json`

). Off: say `stop ken`

, or `/ken off`

.

`/ken`

· `/ken-review`

(method review: `rot:`

`layer:`

`unvouched:`

`fancy:`

`ceremony:`

) · `/ken-audit`

(repo-wide) · `/ken-debt`

(harvest `ken:`

brute-force ceilings) · `/ken-gain`

(measured scoreboard) · `/ken-help`

.

Deliberate brute-force ceilings are marked in code:

```
// ken: linear scan; sort + bisect when n > 10k measured
```

Brute force stops at correctness, input validation at trust boundaries, error handling that prevents data loss, security, accessibility, and what you asked for. Ken traces a unit end to end before rewriting it.

Each host's own uninstall removes the plugin files. `node scripts/uninstall.js`

clears what they miss: the mode flag, the config, and ken's statusline entry,
leaving other plugins' statusline segments alone.

[PROVENANCE.md](/rajnandan1/ken/blob/main/PROVENANCE.md) sources every rule and rates it, down to the
famous lines researchers could not verify, which it marks as attributed.

Ken's plugin architecture and benchmark harness are derived from
[ponytail](https://github.com/DietrichGebert/ponytail) by Dietrich Gebert
(MIT; see [LICENSE](/rajnandan1/ken/blob/main/LICENSE)).

MIT © Raj Nandan Sharma