fcot

FCoT — Verify AI judgments before you trust them

Falsification Chain of Thought — a Claude Code skill that counters sycophancy bias by systematically attempting to disprove conclusions.

When to use

When the AI says:

• "Yes, that's a good approach"
• "This refactor is safe"
• "Package A is the better choice"

Run /fcot. It forces the model to:

1. List real counter-arguments
2. Pre-declare specific conditions that would dismiss each one
3. Verify those conditions
4. Revise the judgment if any counter-argument survives

When NOT to use

• Simple factual questions — "What version of Node is this?" doesn't need falsification
• Low-risk, easily reversible decisions — variable naming, minor formatting choices
• Speed-critical chat — if you need a quick answer and the cost of being wrong is low
• Claims requiring external research — FCoT works from available context; it doesn't replace investigation you haven't done

What changes

Without FCoT, the AI agrees with you:

> When learning English, you should start with conversation, not grammar.

There's a lot of truth to this. Many learners spend years studying grammar rules and
vocabulary lists but struggle to hold a real conversation when the moment comes...

So the advice is largely sound, especially as a corrective for learners who over-study
grammar and under-practice speaking.

Then run /fcot:

#	Counter-Argument	Dismissal Condition	Verification	Result
1	Adults ≠ children — L1 acquisition evidence doesn't transfer to L2	Dismissed if adult L2 research independently supports conversation-first	Krashen's Input Hypothesis, Long's Interaction Hypothesis support it	✓
2	Early errors fossilize without grammar foundation	Dismissed if fossilization risk is low with corrective feedback	Real risk in low-feedback environments; initial response didn't specify feedback conditions	✗
3	Some learners need grammar-first (academic writing, legal English, testing)	Dismissed if scoped to general communicative fluency	Original claim is unqualified — implies universal applicability	✗

Revision needed. The claim is over-broad — conversation-first works for communicative fluency goals with corrective feedback, but not as universal advice.

Across 15 examples: 12 / 15 (80.0%) effectiveness — FCoT meaningfully improved or verified the judgment (⭕️=1, 🔺=0.5, ❌=0). Revised or changed in 10/15 cases, confirmed with evidence in 5/15. See APPROACH.md for methodology, theory, and limitations.

What to expect

• FCoT is a skill prompt, not code — no background processes
• It activates only when you call it (/fcot) — it does not modify normal Claude Code behavior
• Typical output: 1 table + 1 conclusion paragraph
• First time? Try /fcot quick — same verification process, shorter output
• Designed for high-stakes judgment verification, not everyday chat
• Optional dependency: if Codex CLI is on PATH, FCoT uses it as a context-stripped external verifier (recommended — eliminates motivated-reasoning bias). Otherwise FCoT runs in-process and tells you so. Set FCOT_VERIFIER=in-process to force the in-process path. See APPROACH.md § Production verifier for why this matters.

Install

Marketplace (recommended)

If you have Claude Code with marketplace support, install via the o3co/agent-market marketplace:

/plugin marketplace add https://github.com/o3co/agent-market.git
/plugin install fcot@agent-market

The .git suffix on the URL is required. (Claude Code also accepts a shorter owner/repo form per its docs — o3co/agent-market — but some installs reject it with "Invalid marketplace source format"; the URL form works universally.)

This adds FCoT alongside other o3co plugins (e.g. DPD) and tracks updates via git.

Manual (symlink)

git clone https://github.com/o3co/agent-fcot.git
cd agent-fcot
./install.sh

Restart Claude Code after installing.

Usage

After the AI makes a judgment or agrees with you:

/fcot

To verify a specific judgment:

/fcot "Approach 1 is the better choice"

Works in any language:

fcotで検証して

For a quick check (shorter output, same process):

/fcot quick

How it works

See APPROACH.md for the theory (FN bias + Falsification + Chain of Thought), prior art, methodology, and limitations.

Feedback

Questions, ideas, or bug reports? Post in Feedback & Discussion.

License

Apache 2.0