Big If True

When you send your draft to Big If True, it comes back with the checked claims underlined. For each one, you can see what Claude found and why it reached that conclusion.

There are three verdicts:

Supported

Two independent sources agree, or one definitive source settles it.

Couldn’t verify

Claude can’t prove it either way. Often a quote only you heard, or a document only you have.

Needs review

Something could be off here. Have a look.

We tested Big If True on published articles with known errors and on drafts where we planted mistakes. In our tests, Claude extracted more claims, found real errors, and made fewer incorrect flags with the skill than without it.

Read about the tests and what we found →

Big If True is a skill: a set of instructions you add to Claude once. The skill is free. We recommend using it in Claude Cowork, which requires a paid Claude plan.

Set up once

1. Turn on the toolsIn Claude settings, enable:
   • Capabilities → Web search. It’s what the skill uses to check claims.
   • Capabilities → Code execution and file creation. It lets the skill work in steps, check an article’s internal math, and create the final report.
2. Upload the skillDownload the skill file, then upload it in Claude settings at Customize → Skills.
   • Anthropic’s guide to using skills in Claude shows where the buttons are. If you’re new to skills, here’s what they are.

Check a draft

Open a new conversation in Claude Cowork. Paste or upload your draft and ask Claude to fact-check it. Once Big If True is installed, it will be used automatically. If you’ve connected Google Drive or Notion, you can point it at the document there as well.

Choose a model

Our recommendation is Fable 5.1 for the most rigorous check, or Opus 5 as the economical starting point. Use at least Medium thinking effort; choose High or above for a more thorough check.

It works through claims in batches, so a full check can take a while. When it finishes, open the report to see the findings and their sources.

Big If True looks for sources in the language of your text. When relevant sources block AI access or aren’t online, it has less evidence to work with.

It also needs your reporting. Claims based on interviews, notes, or private documents may come back as “couldn’t verify” unless you provide that material. Upload supporting documents alongside your draft when your privacy settings and reporting obligations allow it. If a missing document could settle a claim, the skill is instructed to ask for it.

As always with AI, Big If True can still get things wrong. Give the results a look before making changes.

We’ll keep improving Big If True. Subscribe to our newsletter and we’ll tell you when a new version ships.

And if Big If True catches something before your readers do, we’d love to hear about it: [email protected].