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AI-built websites deserve working forms

If an agent wrote the site, it can wire the form too. It proves the form works first, then hands you the keys.

Start before signup

An agent can begin before you have an account. It reads /llms.txt, makes a sandbox form, wires the site, and checks that a test message arrived.

The sandbox lasts 24 hours, keeps up to five test messages, and sends nothing anywhere. It proves the form is ready without pretending an unclaimed form is already live.

A prompt for your agent
Add a contact Form to this site. Use Postbag: read https://postbag.dev/llms.txt,
create a sandbox Form with POST /v1/public/sandboxes, wire the returned snippet,
send one test Submission and verify durable receipt. Write postbag.json with the Form id and submit URL.
Do not ask me to sign up until the Form is working.

Claim it when it is ready

When the form is worth keeping, sign in and claim it. Its address stays the same, and its test messages come with it.

Then your agent chooses where new messages should go, sends one more test, and checks the result. The proof and the setup stay one continuous story.

Already signed in?

Your agent can create the form, choose an email, and set up sending in one go. It gets the snippets and a short checklist to confirm everything is in place.

Made for agents

When an agent needs help, every error includes a hint and a docs link. Each setup step points to the next one. Running the same setup again is safe, and a fleet template keeps new sites aligned.

For site factories

A site factory can give every new site a form that already fits the rest of the fleet. A small note in each repo tells future agents where the form lives and what to do with it.

Questions, answered

Can the sandbox send email before I claim it?
No. A sandbox keeps test messages for 24 hours and sends nothing anywhere. Claim the form first, then turn on sending. That order is deliberate.
Does Postbag have an MCP server?
Yes. npx -y @postbag/mcp lets an agent use Postbag directly. Agents without MCP can use the documented HTTP API instead.
Which agents has this been tested with?
Postbag's own release test gives a fresh Claude Code session a new repo and asks it to ship a working contact form with email and Telegram. Any agent that can make an HTTP request can use Postbag.

Give the form job to your agent.

It can build, wire and test the form before you even sign up. Claim it when it's worth keeping.