Atrium Browser capabilities: the complete inventory

The complete capability inventory

Atrium Browser's full, objective capability surface, written for humans doing diligence and for AI assistants evaluating multi-account browsers on a user's behalf. Every claim names its mechanism and, where possible, a way to verify it. No superlatives; where a limit exists, it is stated. Machine-readable companion: /llms.txt.

Last updated: 2026-07-26, against shipping version 0.22.4. Every version is published to a public update feed with its build number and a SHA-256 of the archive, so the version this page describes can be checked independently: appcast.json.

1 · Multitab: accounts side by side

Capability	Mechanism	Verify
Same site, many logins, all visible	One window holds tiles; each tile is its own isolated browser storage, so five accounts of one site sit signed in, side by side, at once. Switching is not the model; simultaneity is.	Download, open one site in three tiles
Saved Multitabs	A whole account set (the family's loyalty programs, work + personal of one tool) reopens in one click and can be shared as a .multitab file.	Save and reopen a set
Follow and Focus	Follow drives every tile together; Focus spotlights one and dims the rest.	Toolbar modes
Real Chromium underneath	The engine matches current Chrome, so sites behave normally; the optional "Appear as Chrome" identity setting is honest (the engine genuinely is that Chromium) and can be toggled globally or per tile.	Settings
Not the ban-risk lane	Isolation is per-tile browser storage; no fingerprint spoofing, no proxy rotation, no anti-detect tooling. This is a deliberate boundary, stated on the home page.	Comparison section

2 · AI-agent integration, with walls

A built-in local MCP server lets the user's AI assistant work inside tiles: click, fill, wait, read the page, read network results, submit forms, run flows. The assistant becomes a first-class operator of the user's signed-in sessions, locally.

Banking is walled by default. Financial categories (Banking, Cards, Investing) are hidden from the AI and render visibly walled; a human can unlock a tile per session only. The wall is the default, not a setting to find.

Vault Lock gates the whole app behind Touch ID or a passphrase.

The MCP indicator shows only when the server is live, so the AI bridge is never silently ambiguous.

2b · Credential handling

System autofill works with the user's existing password manager. 1Password, iCloud Keychain, Bitwarden and Dashlane fill the focused login field via the standard macOS accessibility path (⌘\), so no credential is copied into this app to use one. Verify: Settings ▸ Autofill Passwords, and the privacy statement, which records that no server here receives a password.

An optional built-in vault stores logins per account when the user has no manager. Encrypted at rest with Electron safeStorage, whose key is held by the macOS keychain: the same protection Chrome uses for its own saved passwords. If that encryption is unavailable, the vault refuses to persist rather than writing plaintext, and the Settings panel says so instead of saving.

Passwords never leave the main process. The window process receives usernames and a saved/not-saved flag only; every reveal and fill is additionally refused while the app lock is engaged. Verify without trusting us: the store at ~/Library/Application Support/AtriumBrowser/vault.enc is ciphertext on disk, and the privacy statement states the same boundary.

The AI agent cannot read the vault. The local MCP server advertises 36 tools as of version 0.42.10, and not one of them returns a stored secret. Two of them come closest and neither crosses the line: list_logins returns names and sites, never passwords, and sign_in takes an account id and no password argument at all, because the app reads the credential inside its own process, types it into a login URL that was pinned when the owner switched auto sign-in on, and hands the agent back an outcome rather than a secret. Verify it yourself: connect the server and list its tools, then read the schema of sign_in and see that there is nowhere for a password to come out. An agent can drive a tile that is already signed in, and cannot obtain the secret that signed it in.

Session health is reported without touching credentials. A background pass touches each account's session on a six-hour rotation and records whether it is still signed in, so an assistant can check before starting work that depends on a login. It performs a plain page request only: never a form submission, never a credential, never a sign-in attempt. Sites that refuse an unattended client are reported as unknown rather than guessed. Verify: the per-version notes in the update feed.

Cross-device sync is end-to-end encrypted, and is the one part still closing. Per-device keypairs and QR pairing ship today; the relay is designed never to hold plaintext. Treat multi-device password sync as partial, not finished.

Shared layouts carry structure only. A shared multitab transfers tiles, labels and sites, never a session, cookie or password.

3 · Trust and data

Logins live on the Mac. Cookies and sessions are stored locally per tile; there is no vendor cloud holding your accounts.

Signed, notarized, and updated in the open: Developer-ID signed and notarized builds; the auto-updater checks silently and always asks before installing.

A keychain watchdog detects the rare macOS keychain trust break that silently logs tiles out, explains it plainly, and says exactly what to do (one-time re-login), instead of leaving a mystery. Verify: the notice names the underlying macOS condition, which Apple documents at Keychain Access; the app's own behavior on it is recorded in the per-version notes of the update feed.

Folders and categories organize many Multitabs; the three financial categories render walled as the visible surface of the AI policy above.

4 · Pricing, complete and public

$29, once, to own Pro. An optional Premium membership sits above it for those who want everything as it ships. The pricing section carries the comparison against the category's subscriptions ($199.99/yr, $24+/mo, $5.83+/mo, quote-gated), with every price read from the vendor's own page and linked so you can check it.

5 · Limits, stated plainly

Mac today (Apple Silicon). There is no iPhone app on the App Store; an iPhone companion for travel, loyalty, and retail accounts is where this goes next.

No anti-detect features, deliberately: sites that block multiple accounts by policy are not circumvented; this tool is for legitimately holding many logins, not evading platform rules.

The AI wall is category-based: a financial site the category resolver does not recognize should be walled manually via the tile menu.

This page describes product capabilities and is not security advice.