FormThunder documentation
FormThunder is a form backend built for AI to configure. These docs cover posting a form to it, customising and protecting that form, and matching the emails to your brand. They also cover webhooks and integrations, the MCP server, the CLI, the REST API and agency accounts. New here? Start with the quickstart.
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Forms
Submit API and fieldsHow POST /submit works: content types, every reserved field, the JSON response and each status code.Customise a formSet the email subject, from name, reply-to, CC and redirect, and choose where visitors land after sending.Spam protectionStop form spam with hCaptcha, Turnstile, reCAPTCHA v3, a honeypot, the content filter, domain restriction and report spam.Attachments and uploaderAccept files in a form: direct multipart uploads up to 5 MB, and the advanced uploader up to 25 MB per file.
Emails
Email templates and brand kitMatch notification emails to your site with the brand kit, built-in themes or custom HTML templates.Template variablesEvery mustache variable you can use in an email template and subject line, with an example.AutoresponderSend an automatic reply to the person who submitted a form, with the rules that keep it from being misused.
Deliveries
AI and tools
MCP serverConnect Claude Code, Cursor or any MCP client to FormThunder: install commands, the hosted endpoint, tools and prompts.CLIInstall and use the formthunder CLI: login, forms, brand kit, templates, tests and clients, all with --json output.REST API referenceThe FormThunder REST API v1: authentication, error format and every endpoint for forms, submissions, templates and clients.