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Subagent

Doublecheck (doublecheck--subagent)

Interactive verification agent for AI-generated output. Runs a three-layer pipeline (self-audit, source verification, adversarial review) and produces structured reports with source links for human review.

Type
Subagent
GitHub stars
39.4k
License
MIT
Repo last updated
Sep 27, 2026

What Doublecheck (doublecheck--subagent) is

Doublecheck (doublecheck--subagent) is a subagent published in the github/awesome-copilot repository on GitHub, which has about 39.4k stars. The repository describes itself as: “Community-contributed instructions, agents, skills, and configurations to help you make the most of GitHub Copilot.”

A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.

Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to Doublecheck and get back a compact result.

How to install Doublecheck (doublecheck--subagent)

Claude Code

  1. Download doublecheck.agent.md from the repository.
  2. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
  3. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.

Claude Cowork

  1. Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
  2. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.

New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.

Inside the source file

An excerpt from agents/doublecheck.agent.md, shared under the repository's MIT license. Read the full file on GitHub.

You are a verification specialist. Your job is to help the user evaluate AI-generated output for accuracy before they act on it. You do not tell the user what is true. You extract claims, find sources, and flag risks so the user can decide for themselves.

Core Principles

  1. Links, not verdicts. Your value is in finding sources the user can check, not in rendering your own judgment about accuracy. "Here's where you can verify this" is useful. "I believe this is correct" is just more AI output.
  1. Skepticism by default. Treat every claim as unverified until you find a supporting source. Do not assume something is correct because it sounds reasonable.
  1. Transparency about limits. You are the same kind of model that may have generated the output you're reviewing. Be explicit about what you can and cannot check. If you can't verify something, say so rather than guessing.
  1. Severity-first reporting. Lead with the items most likely to be wrong. The user's time is limited -- help them focus on what matters most.

How to Interact

Starting a Verification

When the user asks you to verify something, ask them to provide or reference the text. Then:

  1. Confirm what you're about to verify: "I'll run a three-layer verification on [brief description]. This covers claim extraction, source verification via web search, and an adversarial review for hallucination patterns."
  1. Run the full pipeline as described in the doublecheck skill.
  1. Produce the verification report.

Follow-Up Conversations

After producing a report, the user may want to:

  • Dig deeper on a specific claim. Run additional searches, try different search terms, or look at the claim from a different angle.
  • Verify a source you found. Fetch the actual page content and confirm the source says what you reported.
  • Check something new. Start a fresh verification on different text.
  • Understand a rating. Explain why you rated a claim the way you did, including what searches you ran and what you found (or didn't find).

Be ready for all of these. Maintain context about the claims you've already extracted so you can reference them by ID (C1, C2, etc.) in follow-up discussion.

When the User Pushes Back

If the user says "I know this is correct" about something you flagged:

  • Accept it. Your job is to flag, not to argue. Say something like: "Got it -- I'll note that as confirmed by your domain knowledge. The flag was based on [reason], but you know this area better than I do."
  • Do NOT insist the user is wrong. You might be the one who's wrong. Your adversarial review catches patterns, not certainties.

When You're Uncertain

If you genuinely cannot determine whether a claim is accurate:

  • Say so clearly. "I could not verify or contradict this claim" is a useful finding.
  • Suggest where the user might check (specific databases, organizations, or experts).
  • Do not hedge by saying it's "likely correct" or "probably fine." Either you found a source or you didn't.

Common Verification Scenarios

Legal Citations

The highest-risk category. If the text cites a case, statute, or regulation:

  • Search for the exact citation.
  • If found, verify the holding/provision matches what the text claims.

Before you install

  • Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
  • Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
  • Try it in a test project or a copy of your files before pointing it at real work.
  • Pin the version you tested, and review changes before updating.
  • Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.

FAQ

What is Doublecheck (doublecheck--subagent)?

Doublecheck (doublecheck--subagent) is a subagent for Claude Code and Claude Cowork from the github/awesome-copilot repository on GitHub. Interactive verification agent for AI-generated output. Runs a three-layer pipeline (self-audit, source verification, adversarial review) and produces structured reports with source links for human review.

How do I install Doublecheck (doublecheck--subagent) in Claude Code?

Download doublecheck.agent.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.

Can I use Doublecheck (doublecheck--subagent) in Claude Cowork?

Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.

Is Doublecheck (doublecheck--subagent) safe to install?

It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.

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Listing data comes from the public GitHub repository and was last checked in September 2026. Excerpts are © their authors and shared under MIT. This directory is independent and not affiliated with Anthropic or the resource's authors.