# What does Castle use? Castle (castle.io) shows public evidence of 30 tools, according to runsonwhat (last checked 2026-11-13). - Industry: Security - Size: 11–50 employees - Based in: San Francisco, United States - LinkedIn: https://www.linkedin.com/company/castle-intelligence ## Edge & Hosting | Tool | Category | Evidence | Since | |---|---|---|---| | [Cloudflare](https://www.runsonwhat.com/reverse/cloudflare) | CDN & Edge | Website code | | | [Amazon Web Services](https://www.runsonwhat.com/reverse/aws) | Hosting & Cloud | Website code | | | [Amazon Route 53](https://www.runsonwhat.com/reverse/route53) | DNS | DNS records | | | [Amazon CloudFront](https://www.runsonwhat.com/reverse/cloudfront) | CDN & Edge | Custom domain | | | [Netlify](https://www.runsonwhat.com/reverse/netlify) | Hosting & Cloud | Custom domain, DNS records, Website code | | ## Application | Tool | Category | Evidence | Since | |---|---|---|---| | [Tailwind CSS](https://www.runsonwhat.com/reverse/tailwind) | Frontend | Website code | | | [Astro](https://www.runsonwhat.com/reverse/astro) | Frontend | Website code | | ## Data & Observability | Tool | Category | Evidence | Since | |---|---|---|---| | [Google Analytics](https://www.runsonwhat.com/reverse/ga) | Analytics | Website code | | | [Google Tag Manager](https://www.runsonwhat.com/reverse/gtm) | Analytics | Website code | | | [web-vitals](https://www.runsonwhat.com/reverse/web-vitals) | Monitoring | Website code | | | [PostHog](https://www.runsonwhat.com/reverse/posthog) | Analytics | Website code | | | [Atlassian Statuspage](https://www.runsonwhat.com/reverse/statuspage) | Monitoring | Custom domain, DNS verification records, Email records, Website code | | | [Segment](https://www.runsonwhat.com/reverse/segment) | Analytics | Website code | | ## Go-to-market | Tool | Category | Evidence | Since | |---|---|---|---| | [Google Ads](https://www.runsonwhat.com/reverse/google-ads) | Ads & Pixels | Website code | | | [LinkedIn Insight Tag](https://www.runsonwhat.com/reverse/linkedin-insight) | Ads & Pixels | Website code | | | [ActiveCampaign](https://www.runsonwhat.com/reverse/activecampaign) | Marketing | Email records, Website code | | | [Intercom](https://www.runsonwhat.com/reverse/intercom) | Support & Docs | Email records | | | [ReadMe](https://www.runsonwhat.com/reverse/readme) | Support & Docs | Custom domain | | | [Ghost](https://www.runsonwhat.com/reverse/ghost) | Website & CMS | Custom domain | | ## Company Ops | Tool | Category | Evidence | Since | |---|---|---|---| | [Microsoft 365](https://www.runsonwhat.com/reverse/microsoft-365) | Workspace | DNS verification records | | | [Google Workspace](https://www.runsonwhat.com/reverse/google-workspace) | Workspace | Email records, Website code | | | [SendGrid](https://www.runsonwhat.com/reverse/sendgrid) | Email Delivery | Custom domain, Email records, Website code | | | [Atlassian](https://www.runsonwhat.com/reverse/atlassian) | Dev Tools | DNS verification records | | | [Slack](https://www.runsonwhat.com/reverse/slack) | Collaboration | DNS verification records | | | [Cursor](https://www.runsonwhat.com/reverse/cursor) | Dev Tools | DNS verification records | | | [Notion](https://www.runsonwhat.com/reverse/notion) | Collaboration | DNS verification records | | | [Vanta](https://www.runsonwhat.com/reverse/vanta) | Security & Compliance | Custom domain | | | [Zapier](https://www.runsonwhat.com/reverse/zapier) | Dev Tools | DNS verification records | | ## FAQ ### What tools does Castle use? As of November 2026, runsonwhat has found 30 tools at Castle (castle.io) in public records. Edge & Hosting: Cloudflare, Amazon Web Services and Amazon Route 53. Application: Tailwind CSS and Astro. Data & Observability: Google Analytics, Google Tag Manager and web-vitals. Go-to-market: Google Ads, LinkedIn Insight Tag and ActiveCampaign. Company Ops: Microsoft 365, Google Workspace and SendGrid. Last checked November 13, 2026. ### What cloud does Castle run on? Castle uses Amazon Web Services for hosting and cloud infrastructure, alongside Netlify, according to runsonwhat (November 2026). runsonwhat found Amazon Web Services through Amazon Web Services code on castle.io. Amazon Web Services is used by 147,730 companies runsonwhat tracks. ### What email provider does Castle use? Castle uses Microsoft 365 for email and office software, alongside Google Workspace, according to runsonwhat (November 2026). runsonwhat found Microsoft 365 through a DNS verification record for Microsoft 365. Microsoft 365 is used by 739,093 companies runsonwhat tracks. ### What does Castle use for customer support? Castle uses Intercom for customer support and documentation, alongside ReadMe, according to runsonwhat (November 2026). runsonwhat found Intercom through email records that authorize Intercom. Intercom is used by 9,217 companies runsonwhat tracks. ### What analytics tools does Castle use? Castle uses Google Analytics for analytics, alongside Google Tag Manager, PostHog and Segment, according to runsonwhat (November 2026). runsonwhat found Google Analytics through Google Analytics code on castle.io. Google Analytics is used by 905,009 companies runsonwhat tracks. ### What is Castle's website built with? Castle uses Ghost for its website, according to runsonwhat (November 2026). runsonwhat found Ghost through a subdomain that points at Ghost. Ghost is used by 903 companies runsonwhat tracks. ### Does Castle use Cloudflare? Yes. runsonwhat found Cloudflare at Castle through Cloudflare code on castle.io. Cloudflare is a CDN & Edge tool used by 737,445 companies runsonwhat tracks. ### Which companies have a tech stack similar to Castle's? The companies with the stacks most like Castle's are eAI, Quickwork, Streamlinehq and stakefish, according to runsonwhat (November 2026). Each shares 5 to 13 tools with Castle, and rare tools count for more than common ones like Google Workspace, so the match reflects real stack choices. ### How does runsonwhat know what Castle uses? runsonwhat reads public records only. Of the 30 tools at Castle, 11 were found through code on castle.io, 8 through DNS records, 7 through subdomains that point at the vendor, 3 through email records and 1 through website configuration files. A tool is listed only when a direct record backs it up; DNS is rechecked weekly and castle.io about monthly. --- Source: runsonwhat, https://www.runsonwhat.com/company/castle.io (updated November 2026). Counts are companies with direct public evidence of the tool (DNS records, certificates, website code, a real-browser crawl, subprocessor lists), so they are lower bounds. Methodology: https://www.runsonwhat.com/methodology.