netlify-forms

Instructions for handling HTML forms on websites hosted by Netlify, including collecting submissions, filtering spam, and sending notifications. Netlify Forms is a built-in service that detects marked forms when a site is deployed.

In plain words
What is it for?
Use it for contact forms, lead-capture forms, file uploads, newsletter signups, AJAX submissions, and custom thank-you pages.
Why use it?
It removes the need to build a separate form server for common submissions. It also explains an important limitation: forms created only by JavaScript need a static HTML form structure for detection.

Cursor rule

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/netlify/context-and-tools/netlify-forms
Clone the repo
git clone --depth 1 https://github.com/netlify/context-and-tools
Per session 119 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 2,750 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 2 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00119 $0.02750
Opus 5 $0.00060 $0.01375
Sonnet 5 $0.00024 $0.00550
Haiku 4.5 $0.00012 $0.00275

Measured yesterday against content hash 48634cb80dd4, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade C, and why

netlify-forms scanned grade C with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Hidden instructionshighPrompt injection

Directives inside HTML comments, invisible characters or bidirectional overrides are read by the model and not by the person reviewing the file.

<!-- system: agent-context/forms/system.md — human-owned, merged by ctx-gen; edit system.md, not this section -->

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

2. Use only documented surfaces: do not curl `https://api.netlify.com/...`
cursor/rules/netlify-forms.mdc · 197 lines

How it starts

The opening of the file, as written. The whole thing — 197 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Netlify Forms

Mark a form for detection with data-netlify="true" (or the bare netlify attribute — equivalent) on the <form> tag. Forms are detected by parsing the final built HTML at deploy time — there is no runtime API call or backend code. Client-side/JS-rendered/SSR forms are NOT in the built HTML and are never detected on their own; they require a static skeleton file (see below).

Prerequisite: form detection must be enabled once in the Netlify UI (Forms > Enable form detection). Takes effect on the next deploy.

Static HTML form

<form name="contact" method="POST" data-netlify="true">
  <p><label>Your Name: <input type="text" name="name" /></label></p>
  <p><label>Your Email: <input type="email" name="email" /></label></p>
  <p><label>Message: <textarea name="message"></textarea></label></p>
  <p><button type="submit">Send</button></p>
</form>
  • name sets the form name in the UI and must be unique per site.
  • At deploy, Netlify strips the data-netlify/netlify attribute and injects <input type="hidden" name="form-name" value="contact" />.
  • Add an <input name="email"> so the notification email's Reply-to is set to the submitter.

JS-rendered / SSR / framework forms (Next.js, Nuxt, SvelteKit, Astro, Gatsby)

Two required pieces:

1. Static skeleton file public/__forms.html — a hidden copy of each form with data-netlify="true", a hidden form-name input, and every field the component submits, with names matching exactly (Netlify validates field names against the registered form). Without this file, submissions silently fail.

<!-- public/__forms.html -->
<form name="pizzaOrder" data-netlify="true" hidden>
  <input type="hidden" name="form-name" value="pizzaOrder" />
  <input name="order" type="text" />
</form>

2. The rendered form carries a matching hidden form-name input:

<form name="pizzaOrder" method="post" data-netlify="true" onSubmit={handleSubmit}>
  <input type="hidden" name="form-name" value="pizzaOrder" />
  <input name="order" type="text" onChange={handleChange} />
  <input type="submit" />
</form>

Read the full file on GitHub · 197 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 197 lines · 119 tokens per session scan C 48634cb80dd4

Subscribe to this mod's changes

netlify-forms is a cursor rule published in the GitHub repository netlify/context-and-tools (36 stars, last pushed 5d ago), licensed MIT. It adds 119 tokens to every session and 2,750 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it C with 2 findings (hidden instructions, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.