smolboid is a small daemon that serves [twtxt](https://twtxt.readthedocs.io/) feeds for many users and lets them publish and manage their feed by sending ordinary [smolmail](https://code.randogoth.com/randogoth/smolmail). A post is a mail body; management rides custom frontmatter fields. Every published record carries the author's own smolmail payload signature, so any reader can verify authorship offline against the author's key alone — the host can withhold records but cannot forge one. No extra client tool is needed: any conformant smolmail client can post, and legacy twtxt and Yarn clients read the feeds unchanged.
The workspace is `core/`, the feed format and verification library with no I/O, and `daemon/`, the server binary. [audit.md](audit.md) records the security audit, its findings and the test suites that prove them.
## Build and test
devbox manages the toolchain; every script runs in it.
```
devbox run build # compile the workspace
devbox run test # unit, property and vector tests
devbox run vectors # regenerate and pin core/vectors.json
devbox run rig # end-to-end against a local bunshin, the fumi CLI as author
devbox run stress # mail flood, quotas, reply budget, HTTP load
devbox run pentest # adversarial probes, raw sockets and real mail
devbox run audit-deps # cargo audit over the dependency tree
```
## Running an instance
The daemon holds one smolmail identity — a 32-byte master key — and one mailbox, e.g. `twtxt@smol.place`. Bootstrap its mailbox once with the fumi CLI against the same key and store, because the first server pin and the registration are operator actions:
Posting needs an accept token (§5.8), and a feed exists only once its owner's address has been verified. There are two ways to get there.
**By mail, if `registration` is `open`.** An author writes to the mailbox; the daemon replies telling them how to register; they send `Twt-Register` and get a feed, a token and a confirmation. No operator action at all. See [The author's side](#the-authors-side).
Before the daemon answers an unknown sender *at all*, it resolves the address their signed `Reply-To` claims, on that address's own server, and requires the resolved key to equal the key that signed the mail. The claim alone proves only that the sender signed that URI — not that they hold the mailbox it names — so without this check a signed `Reply-To` naming someone else's address would be enough to take their feed. Replying to the claimed `smol://` URI would be worse still: it would pin the sender's key as verified under that address, and the real owner could never register afterwards.
`registration` is `silent` by default, which drops unknown senders without a reply exactly as every version before self-service did. `closed` tells them registration is shut. An admin can change it by mail, so the mode lives in `state.json` and the config key is only its initial value.
`admit` passes no expected key, because the target has not written in — it prints the resolved key and fingerprint for an out-of-band check instead. A mail-driven registration always passes one.
## Admin commands
Listed addresses in `admins` may run these by mail, from their own address, so an instance can be operated without shell access:
| Field | Value | Effect |
| --- | --- | --- |
| `Twt-Admit` | an address | Verify, accept and create that author's feed |
| `Twt-Block` | an address | Withdraw their token; the feed keeps being served |
| `Twt-Registration` | `open` \| `closed` \| `silent` | Change who may register |
An admin's own mail reaches the main tier only once the daemon holds a token for them, so admit your admin identity once with the CLI; until then the acks arrive in your requests tier. An admin with no feed still has to prove they hold their address, by the same resolve as any stranger: a signed `Reply-To` naming an admin proves nothing on its own.
A non-admin sending one of these gets the ordinary answer for their situation and is never told that admin commands exist.
Then fetch the reply — it carries the accept token that moves your posts out of the requests tier — and post by sending the twt as the mail body, from any smolmail client:
**Do not accept the daemon's address in your client.** Replies arrive in your requests tier (`fumi list --requests`), which is where to look for them. If you accept the address, your client attaches an accept token to everything you send afterwards — and a published record is verified by rebuilding the exact bytes you signed, which cannot include a token without publishing it. Every post you sent would be refused, with a reply saying so.
The rules the daemon enforces: text is at most `max_post_chars` characters (288 by default; twtxt itself sets no hard limit) and may not contain control characters such as TAB, LF or CR, as twtxt requires, while U+2028 is allowed as the Multiline extension's line break; the timestamp is the mail's own time, pinned by the signature, so a same-second resend is rejected with a reply — wait a second and resend; at 90% of the size cap the daemon mails a warning naming the cap and both prune modes. Error replies are subject to the address's rules: at most ten per sender per hour, never twice for the same rejected payload.
Each record's signature covers the smolmail payload bytes: the author's key, the record's timestamp, and the text in one of the two canonical forms a real client emits (bare, or with the ordinary send's `Reply-To` block). The verifier rebuilds those bytes from the record itself plus the feed's metadata, tries each `smol:host_key` as the recipient, and marks the record verified, unsigned or invalid. `smolboid check` reports exactly that.
Feeds are served at `GET /twtxt/<username>.txt` (`HEAD` answers with the same headers, no body) with a strong SHA-256 ETag, `Last-Modified`, `Cache-Control: max-age=300` and `Access-Control-Allow-Origin: *`; `If-None-Match` takes precedence over `If-Modified-Since`, and both answer 304. Unknown and missing feeds are 404; the listener sheds concurrent-connection floods with 503 and closes stalled connections after ten seconds.
## The deployment trust contract
Read this before running an instance on the public internet.
**TLS is your job.** The listener is plain HTTP. The `base_url` above assumes TLS termination at a reverse proxy in front of the daemon; pointed at the internet directly, it serves feeds — public data — in cleartext, and a network attacker could serve stale or substituted feeds to readers. Terminate TLS upstream, or front the daemon with whatever serves the rest of your domain.
**The first pin is on you.** Bootstrap is trust-on-first-use: `fumi trust` pins your smolmail server's Noise static key and `smolboid admit` resolves each author on their own server with the same semantics. A lying DNS path fails closed at the pin mismatch, but the *first* pin you enter is taken on faith. Verify the server key and your authors' keys out of band before admitting them; `smolboid admit` prints each resolved key.
**The master key is the whole identity.** The 32-byte master at 0600 is the only secret on disk — everything else under `data/` is public keys, counters and ledgers. Back it up, because a lost master means a new identity and a new `smol:host_key` in every feed; a stolen one means an attacker can register the daemon's mailbox elsewhere and post as it, though they cannot forge the authors' records already published.
**One domain per instance.** The feed path is fixed to the author's smolmail username, and discovery resolves `user@domain` to `https://domain/twtxt/<username>.txt`, so one instance serves one domain; multiple domains run multiple daemons.
**Authors own their words, not your storage.** An admitted author can fill their quota daily and switch to FIFO pruning; `cap_bytes` is the bound. An unknown sender publishes nothing and gets no token; with `registration = open` they draw at most one reply telling them how to register, bounded by `info_replies_per_hour` globally and the per-sender hourly budget. With the default `silent` they draw nothing at all.
