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 Big If True than without it.

Read about the tests and what we found →

Big If True is a plugin: a set of instructions and tools you add to Claude once. It’s free, and it works on any paid Claude plan (Pro, Max, Team or Enterprise), in chat, in Claude Cowork and in Claude Code. We recommend Cowork.

Set up once

1. Check that code execution is onIn Claude settings under Capabilities, make sure Code execution and file creation is enabled. It usually is. It lets Big If True work in steps, check an article’s internal math, and create the final report. Web search is built into Claude; on a Team or Enterprise plan, an admin may need to enable both for the whole workspace.
2. Install the pluginOpen Big If True in Claude. Claude asks to add Verso’s plugin marketplace: click Sync, then Add next to Big If True.
   • New versions come through the plugin, so there is nothing to download again when we release one.
   • In Claude Code, add our repository with /plugin marketplace add Verso-Lab/big-if-true-plugin, then run /plugin install big-if-true@verso.
   • The plugin is open source: Verso-Lab/big-if-true-plugin on GitHub.

Uploaded the skill file before? Once the plugin is installed, remove the old copy under Customize → Skills, so Claude uses the plugin and not the older file.

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 5.5 at High thinking effort, which caught as many errors in our latest tests for about two-thirds of the cost. At Medium effort, Opus 5.5 is faster but checks less deeply.

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 is built and tested for Claude. OpenAI’s ChatGPT and Codex support skills too, and you’re welcome to try the skill there (it’s the skills/big-if-true folder on GitHub), but we haven’t optimized that yet. We hope to have a version of Big If True for ChatGPT and Codex, along with a usage guide, soon.

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 can't check claims in your original reporting unless you share it. 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 and reporting obligations allow it, or check those claims yourself. If a missing document could settle a claim, Big If True 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.

Version 0.7.0 September 2026

• Every claim reaches the report. Claude could sometimes merge claims or drop one between finding them and writing the report. Now the list of claims is checked in code, so each one gets its own verdict.
• A plugin, not a file. Big If True now installs as a Claude plugin, and new versions arrive on their own. It replaces the skill file; if you uploaded that before, remove it under Customize → Skills.
• Easier to read at a glance. Supported and couldn’t-verify look clearly different now, including on a phone in bright light.

We’ll keep improving Big If True. Subscribe to our newsletter and we’ll tell you what changed 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].