The page

The page is where you type. offprompt serves it on 127.0.0.1, wherever the agent runs, and it loads nothing from the network. From a cloud sandbox it reaches you through a tunnel, and your values are encrypted before they leave the browser.

Try it

This is offprompt's own page, running here with a stand-in for its server. Fill it, write, and compare the four emoji on the Written page with the agent's side below them.

What follows is each part of it, from top to bottom.

The top bar

offprompt's mark, a line saying whether the page is connected and how long the request has left, and the address the page was served from. The page asks offprompt every ten seconds and keeps that line true: connected, reconnecting, expired, or answered elsewhere.

When offprompt stops answering, or the request closes, a banner says so and the write button waits. Nothing is written until offprompt is back, and nothing once the request is closed.

Who is asking, and why

"Claude Code is asking for five values." The name comes from the host program, which sets it when it connects to offprompt, so the model cannot make it up. Known agents get their own name, and some their logo; any other shows the name it gave. See Agents.

Below it is the agent's reason, rendered from Markdown and labelled as the agent's claim. It can use bold, lists and code. A link in it shows its address as text and is not clickable, because this is a page people type secrets into: the only clickable links on it come from offprompt's registry, on the provider's own domains.

Where it writes

The file, its project, the full path on hover, and a few words on its state: a new file, one that exists and how many of the asked keys it already holds, not gitignored, or tracked by git. From a cloud sandbox it adds that your values are encrypted in the browser.

The page also says before you type anything when the file cannot be written: its folder has to take new files, since the write goes through a temporary file there, and an existing .env has to be readable.

Pasting and importing

A card says a block can be pasted anywhere on the page, with Choose file for a .env.

Paste a block of NAME=value lines into any field and it fills every field it names. Choose a file, or drop one anywhere on the page, and it does the same. The file is read in the page and never uploaded. The block is read as dotenv, the same way offprompt writes it, so quoting, export prefixes and any order survive a copy out of a dashboard.

A banner then says what the fill did: how many fields it filled, how many need a fix, and which keys it skipped because the request did not ask for them. Undo puts the fields back until you type over one.

• A paste that names none of the asked keys lands in the field as an ordinary paste, so a bare key that happens to contain = stays a bare key.
• While a file is dragged over the page, an overlay says what dropping it will do and names the keys it will fill.
• A file that names none of the keys goes whole into the multi-line field it was dropped on, such as a PEM block.
• A request written to a file of its own has no .env card: a file dropped anywhere fills its one field.

Values you already keep turns a password manager or a secrets store into a file to drop here.

The fields

One field per key, in a card headed by the count and a Show values switch.

Each field carries its name, the provider's logo, and on the right the address where the key is made, or what kind of value it is. The caption the agent gave sits under the name. Under the field come its checks, then, where they apply:

• a line for a value nothing checks;
• links to providers where someone who has no value yet can create one, such as Supabase and Neon for a Postgres connection string;
• a notice when the file already holds the key, in orange, since writing replaces it.

Formats that allow several lines, such as pem and json, get a taller field, shown in the clear, and a file picker. A generated key gets a field the page fills as it opens, with Regenerate, or Generate once it is cleared. One the file already holds gets a row saying it is kept.

Masking

Secret values are masked as you type. Show values reveals every one at once; the eye on a field shows or hides that field alone. Values are typed into text areas rather than password inputs, so your browser's password manager does not offer to save a secret as a password.

The checks

Each rule is its own line under the field, such as "starts with re_" or "20 to 80 characters". The page checks the value as it changes, and each line turns green when the value keeps the rule and red when it breaks it.

• While the field has focus, a value that is only short, or only part of the way into its prefix, is not wrong yet: the line says "14 so far" and waits.
• Once every rule passes, the lines fold into one, such as "Looks like a Stripe webhook signing secret", or "Matched from .env.production · …" for a value a file filled.
• A broken line says what it got, such as "got 19" or "got pk_live_", and never more of the value than a prefix that names what it is.
• Paste the publishable key where the secret one goes and the page says so: "That's the publishable key. Use the secret key from the same page." Paste another provider's key and it says whose: "This looks like an OpenAI API key."
• Spaces at either end are pointed out, with Trim. Left in, they are written as typed.
• A single-line field drops line breaks, so a key copied with its trailing newline is stored without it.

offprompt runs the same checks again when you write, and a failure keeps the request open for another try. Every rule, provider by provider, is in Providers and Formats.

Writing

Above the button a bar counts the values ready, and the button says what is left: "Fill 3 values to write", "Fix 1 value to write", then "Write to .env.local". ⌘ or Ctrl with Enter writes from anywhere on the page.

When the file is tracked by git, the page shows an override to tick before the button will write there. That is the one write offprompt holds back on its own.

Either every value is written or none is, in one atomic write. If the file cannot be written, nothing is: your values stay on the page with the error, and Try again writes them once it is fixed.

Written

After the write the page says Written. and shows the fingerprint, four emoji with their names, and how they appear on the agent's side. It lists the file and each key in it as added, replaced, generated or kept. It holds no value, and says the tab can be closed.

Without JavaScript

The page works without its script: the form submits the ordinary way and offprompt checks the values and marks the broken lines under their fields. It cannot keep values it never echoes, so after a failed write it asks for them again. A page opened from a cloud sandbox needs its script, which encrypts the values before they leave the browser.