The request is generic ('check'), so it is unclear what kind of check is meant. The products below cover several distinct kinds of check: Vercel for deployment-style status checks 111, GitHub for AI-output and code verification 212, LanguageTool for grammar and spelling 313, Checkov for infrastructure misconfiguration 4, SonarQube for code quality and security 515, and FactStamp for figure verification 919. Which one fits depends on what you need to check.
A question back: What do you want to check: text grammar, code quality, infrastructure configuration, a deployment status, or the accuracy of a figure or citation?
- 1
LanguageTool APIlanguagetool.orgverified and signed
Checks text for grammar, punctuation and spelling errors in over 30 languages via its POST /check action 13.
official:API · LanguageTool API+1 community tools built for it
for agents: POST /check · GET /words · GET /languages
- 2
SonarQube Cloudsonarsource.comverified and signed
Analyzes source code for bugs, security vulnerabilities and code smells, with a Quality Gate check action that reports whether analysis passed 515.
+19 community tools built for it
for agents: SonarSource/sonarqube-quality-gate-action · SonarSource/sonarqube-scan-action · sonarqube
- 3
GitHubgithub.comverified and signed
Hosts code and offers a doublecheck skill that verifies AI output by extracting claims and finding supporting or contradicting sources 212.
official:CLI · github-mcp-serverskill · add-community-extensionskill · git-commitskill · acquire-codebase-knowledge+2,563 community tools built for it
for agents: doublecheck · ruff-recursive-fix · agent-supply-chain
- 4
FactStampfactstamp.devverified and signed
A paid checkpoint for numbers and dates. verified, stale, contradicted or unknown, cited to a dated primary source. $ FactStamp — figure verification for agents 9
official:MCP server · FactStamp
for agents: check_figure · check_figure · check_vat
- 5
Checkovcheckov.iowebsite read, tools not yet checked
Scans infrastructure as code, container images and open source packages for cloud misconfigurations and vulnerabilities at build time 4.
+1 community tools built for it
Sources
- 1Agentic Infrastructure - Vercelvercel.com · read 2026-10-29
- 2GitHub · Change is constant. GitHub keeps you ahead. · GitHub · GitHubgithub.com · read 2026-10-29
- 3Free AI Grammar Checker - LanguageToollanguagetool.org · read 2026-10-29
- 4checkovcheckov.io · read 2026-10-29
- 5Homepage | SonarQube Cloud | Sonar Documentationdocs.sonarsource.com · read 2026-10-29
- 9FactStamp — figure verification for agentsfactstamp.dev · read 2026-10-29
- 11Vercel API: declares "createCheck" (the record we read and signed)unfragile.ai · read 2026-10-24
- 12doublecheck: declares "doublecheck" (the record we read and signed)unfragile.ai · read 2026-10-24
- 13LanguageTool API: declares "POST /check" (the record we read and signed)unfragile.ai · read 2026-10-24
- 15SonarQube Quality Gate Check: declares "SonarSource/sonarqube-quality-gate-action" (the record we read and signed)unfragile.ai · read 2026-10-24
- 19FactStamp: declares "check_figure" (the record we read and signed)unfragile.ai · read 2026-10-24
For agents: the 10 actions behind this answer
createCheck · Vercel API verified and signed
Creates a new Check
doublecheck · doublecheck verified and signed
Three-layer verification pipeline for AI output. Extracts verifiable claims, finds supporting or contradicting sources via web search, runs adversarial review for hallucination patterns, and produces a structured verification report with source links for human review.
POST /check · LanguageTool API verified and signed
Check a text
· checkov website read, tools not yet checked
Prevent cloud misconfigurations and find vulnerabilities during build-time in infrastructure as code, container images and open source packages with Checkov by Bridgecrew.
SonarSource/sonarqube-quality-gate-action · SonarQube Quality Gate Check verified and signed
Check if a project / analysis passed the Quality Gate check
check-domain · UCP Checker found in code, not yet checked
Check if a domain supports Universal Commerce Protocol (UCP). Returns the UCP status, manifest version, capabilities, response latency, and AI bot access policies (GPTBot, ClaudeBot, Google-Extended, etc.). The domain is automatically normalized (removes protocol, www, paths).
New · NewRelic.Agent.Api verified and signed
seo_quick_check · Remote MCP Server – Professional SEO Checker found in code, not yet checked
Quick SEO health check
check_figure · FactStamp verified and signed
A fact check on a dated figure or statistic against the publisher's own series: verified, stale, contradicted or unknown, with the as-of date. Relevant wherever a number is going onto a page, deck, model or decision. Coverage today is Australian primary sources; anything outside coverage returns unk
Check retraction · Scholar Sidekick verified and signed
Check a work's retraction / correction / expression-of-concern status (Crossref updated-by / Retraction Watch).
Labels are the instruments' verdict and are never changed by ranking. Agents and robots get this same answer as JSON at /api/v1/find?q=…&answer=1 and through the MCP server.