Read from your own Farcaster node

Run your own Snapchain read node and a client that reads from it. Your feed and your posts go through your node. The only outside services the tool calls are the fnames registry and a public Optimism RPC, both to look up your FID.

Quickstart

Three commands. You need a Farcaster account that already has storage rented — use a test account (how to get one).

# 0. Provision the compute
readnode provision --provider aws --username yourname

# 1. Install the read node and wait for it to sync
readnode up

# 2. Open the client
readnode client

--username takes a Farcaster username. For an ENS name like alice.eth, pass --fid <number> instead.

readnode provision creates the machine and installs Docker. readnode up installs Snapchain, starts it, and blocks until the node catches up to the head of the chain. readnode client serves the client on http://127.0.0.1:3939 — import your seed phrase there, issue an app key, and you can read the feed, post, follow and react.

Two things to expect:

• up will sit for several hours on the first run. It is downloading and unpacking a snapshot of the network's state, which ends up around 550 GB.
• No API key from anyone. You need a cloud account to rent the machine, and the cloud bill is the only cost.

What you just built

Two halves that talk to each other:

        ┌──────────────────────────────┐
        │  your Snapchain read node    │   reads: feed, casts, reactions
        │  :3381 HTTP   :3383 gRPC     │   writes: relayed to validators
        └──────────────────────────────┘
                    ▲            │
        reads ──────┘            └────── writes
                    │                      │
        ┌──────────────────────────────┐   │
        │  your client  :3939          │   │
        │  holds a scoped app key      │───┘
        └──────────────────────────────┘

The rest of this tutorial explains why it is shaped that way.

Before you start: a test account

The client needs the seed phrase of a Farcaster account that already has storage. Make a new account for this. Do not use your main one.

Two ways to get one:

• The official Farcaster app at farcaster.xyz. Sign up with a new account; the app registers the FID, rents storage and sets a username for you. Its recovery phrase, shown in the app's settings, is the seed phrase this tutorial asks for.
• Onchain, yourself. Register an FID through the IdGateway (or the Bundler, which also rents storage) on OP Mainnet. The official create an account guide walks through it. This costs a small amount of ETH on Optimism.

Part 1 · Farcaster is two systems

Farcaster keeps identity onchain and data offchain. Almost every confusing thing about the protocol comes from that split, so start here.

Onchain — a handful of contracts on OP Mainnet (chain id 10). Three things happen there: creating an account, paying for storage, and authorizing keys. These are rare events, so they are allowed to be slow and cost gas.

Offchain — everything else: posts, follows, reactions, profile edits. This is Snapchain, a peer-to-peer network of nodes. Fast, cheap, signed.

The bridge between the halves is a signature. A message is only valid if it was signed by a key that an onchain contract says belongs to that account.

FIDs

A FID is a Farcaster account number. It is a plain incrementing integer: 1 is the @farcaster account. FIDs are issued by the IdRegistry contract on Optimism.

The protocol is full of integer FIDs, but humans want names, so there is a fnames registry that maps names to FIDs. It is offchain and public:

curl 'https://fnames.farcaster.xyz/transfers?name=farcaster'
curl 'https://fnames.farcaster.xyz/transfers/current?fid=1'

The first response gives you the FID. That is exactly what readnode provision --username yourname does — no key, no account.

Custody addresses

Each FID has a custody address: the Ethereum address that owns it. It can transfer the FID, change recovery, and — this is the part that matters here — authorize and revoke keys.

IdRegistry answers both directions:

idOf(address)   → the FID owned by this address (0 if none)
custodyOf(fid)  → the address that owns this FID

Your seed phrase derives to one Ethereum address. If that address is not the custody address of the FID you are using, nothing else in this tutorial will work — you will get signature errors that look like the node is broken. The client checks this on import and tells you if the match fails.

App keys (signers)

You do not sign messages with your custody key. You sign them with an app key, a separate Ed25519 keypair, and the custody key authorizes it once.

custody key (Ethereum, onchain, guarded)
      │  authorizes, once
      ▼
app key (Ed25519, offchain, scoped, expiring)
      │  signs
      ▼
casts, follows, reactions  →  Snapchain

A leaked app key can post as you until it is revoked or expires. It cannot transfer the FID or authorize other keys.

Storage rent

Writing to Snapchain costs storage, and storage is rented onchain, per FID, in units. Messages of different types consume different amounts — a cast and a reaction are not the same price, and the exact ratios come from the node itself:

curl 'http://127.0.0.1:3381/v1/storageLimitsByFid?fid=1'

That returns each category with a limit and a used count.

Two consequences worth internalizing:

1. Storage is a per-account limit, enforced by the protocol. An FID with no storage cannot write at all. When a category is full, the node prunes the oldest messages in that category to make room for new ones.
2. It is why this tutorial asks for an account that already has storage. Renting storage means sending a transaction on Optimism. This tool never sends a transaction; it only reads Optimism to look up your FID.

Snapchain messages

A message is the unit of everything offchain. It has three parts:

• data — the payload. Type (CAST_ADD, REACTION_ADD, LINK_ADD, USER_DATA_ADD, KEY_ADD, …), the fid that authored it, a timestamp, the body.
• hash — BLAKE3 over the serialized data, truncated to 20 bytes.
• signature + signer — an Ed25519 signature over the hash, and the public key that produced it.

So the order is: serialize data, hash it, sign the hash, attach both. The signature is never part of what gets hashed.

Timestamps are seconds since the Farcaster Epoch, 2021-01-01 00:00:00 UTC — not Unix time. A raw value like 182822400 is a normal 2026 timestamp. When you print one, add 1609459200 first.

Over the HTTP API, hashes and public keys arrive as 0x-prefixed hex and signatures as base64. Over gRPC they are raw bytes. This trips people up when they move a fixture from one to the other.

Part 2 · The read node

Every Snapchain node runs the same binary. One config flag decides its role:

read_node = true    # a read node
read_node = false   # a validator

Read node vs validator

A validator holds a key in the validator set, which is permissioned: you cannot join it by deciding to. A read node is the role anyone can run: it subscribes to decided blocks, verifies the commit certificate against the validator set, applies them, and serves the APIs. Same state, slightly behind, no vote.

That is why this is the role the tutorial uses. It is also why restarting it is free: no consensus is disturbed.

Read nodes take writes, and have no mempool

submitMessage works on both roles. What differs is where the message goes afterwards:

Submitted to a validator — the message enters that validator's mempool for its shard. The validator also gossips it on the mempool topic, so any validator can include it. A message submitted directly to a validator is still proposed by that validator even if gossip drops it elsewhere.

Submitted to a read node — the read node has no mempool of its own. It routes the message to a shard, validates it against that shard's state, gossips it on the mempool topic, and keeps nothing. The message reaches a block only when a validator picks it up from gossip. If that gossip is lost, the message is gone and must be resubmitted.

So: a read node does accept your writes, and it does relay them. It just offers a weaker guarantee than submitting to a validator directly.

The client reads from --node-url and, by default, submits to the same node. If you have access to a validator's HTTP endpoint, split the two:

readnode client --submit-url https://<validator>:3381

Reads still come from your own node; casts, follows, reactions and the KEY_ADD go to the validator. --auth applies to the read node only.

Either way, a 200 from submitMessage means the message validated and was accepted for relay — not that it is in a block. To confirm inclusion, watch for the MERGE_MESSAGE event or read the message back:

curl 'http://127.0.0.1:3381/v1/castsByFid?fid=<you>&pageSize=1&reverse=true'

This is also why mempoolSize: 4294967295 in /v1/info is normal on a read node. That is u32::MAX, meaning "not reported". It is not an overflow, and it is not a symptom of a broken node.

Why the hardware is what it is

16 GB RAM / 4 CPU. The node keeps the full mainnet state in RocksDB.

2 TB of disk. This one surprises people, because the database is much smaller than that:

curl -s localhost:3381/v1/info | jq '.dbStats.approxSize'
# ~548 GB

Two directories live under ~/snapchain:

The snapshot downloads into .rocks.snapshot/ and is unpacked into .rocks/, so for a while both exist: roughly two copies of the state, about 1.1 TB. A 1 TB disk fills up in the middle of the download and the node dies with an unhelpful error. The second terabyte is not headroom for growth; it is required to complete the first sync.

Ports. All three must be reachable from the internet:

3382/UDP carries gossip between nodes, and it is the easiest one to forget, because it is not TCP and you will never curl it. If you are behind a cloud firewall and a host firewall, open it in both.

Watching it sync

readnode status
curl -s localhost:3381/v1/info | jq

blockDelay is how many seconds a shard's newest block is behind the wall clock. While the node catches up it counts down. Once every shard is in single digits, you are in sync. maxHeight differs between shards because each shard is its own chain — do not read a mismatch as a problem.

On a read node, a successful sync shows Processed decided block in the logs. Decided value with round is a validator line; if you see it on a read node, something is misconfigured.

Part 3 · The client

Step 1 — import the seed phrase

The client takes a BIP-39 seed phrase and derives the custody account from it: the address, to look up your FID, and the private key, to sign the authorization in step 2. The phrase is used for that request and never written to disk.

From the custody address it resolves your FID on Optimism with a public RPC endpoint (no key), then confirms custodyOf(fid) is the same address. If it is not, stop: you are about to authorize a key on an account you do not control.

Step 2 — issue an app key

This used to require an Optimism transaction to KeyGateway.add(). It does not anymore. Snapchain accepts gasless signers: you register the key by submitting a KEY_ADD message to a node. No transaction, no gas, about a second.

A KEY_ADD is unusual because it carries two EIP-712 signatures plus the message envelope's own signature, and each does a different job:

1. SignedKeyRequest, from the requesting app. Binds the app's requestFid to the key, so an app cannot claim another app's identity. This is ABI-encoded into the body's metadata field.
2. KeyAdd, from the custody address of the FID receiving the key. This is the actual authorization. It covers the scopes, the TTL and the nonce, so none of them can be altered in flight.
3. The envelope signature, produced by the new Ed25519 key itself — proof that whoever is submitting the KEY_ADD actually holds the private key. This is why KEY_ADD is exempt from the usual "the signer must already be registered" check.

The trap. There are two functions that look interchangeable and are not:

• getSignedKeyRequestMetadata() signs the onchain Farcaster SignedKeyRequestValidator domain — chain id 10, with a verifyingContract.
• getGaslessSignedKeyRequestMetadata() signs the offchain counterpart.

If you build the metadata with the first one and submit it as a KEY_ADD, Snapchain rejects it. Use makeKeyAddBody(), which picks the off-chain variant for you.

Gasless keys differ from the old onchain ones in three ways:

Scopes. Every gasless key declares the message types it may sign. A key scoped to CAST_ADD cannot publish a LINK_ADD. This client requests the set it actually needs:

cast:add, cast:remove, reaction:add, reaction:remove,
link:add, link:remove, user-data:add,
verification:add, verification:remove

KEY_ADD and KEY_REMOVE are never admissible scopes. A signer cannot mint or revoke another signer — if that were possible, one leaked app key would be able to grant itself unlimited successors. Onchain signers predate scoping and have no scopes.

Sliding TTL. Each key carries a TTL of up to 90 days; this client asks for 30. The TTL resets every time the key signs a message that merges, so a key in use stays alive and an abandoned one expires on its own.

Nonces. Each FID has a monotonically increasing user nonce. Every KEY_ADD must carry a nonce strictly greater than the FID's current value, which makes an intercepted authorization unreplayable. Read the current value first:

curl 'http://127.0.0.1:3381/v1/signersByFid?fid=<you>' | jq '.currentUserNonce'

Then submit currentUserNonce + 1. If you are writing retry logic: a retry must re-read the nonce. Replaying the same signed KEY_ADD fails with nonce is not greater than stored nonce, and so does a retry that reused the old value.

Use GET /v1/signersByFid. The older GetOnChainSignersByFid returns onchain keys only and is deprecated — it shows an empty list on an account whose only keys are gasless.

A single FID can hold up to 1000 active gasless keys, counted separately from onchain ones. Gasless signers are live on mainnet as of engine version V16.

Step 3 — read, post, follow, react

Reads go to your node:

curl 'http://127.0.0.1:3381/v1/castsByFid?fid=<you>&pageSize=10&reverse=true'
curl 'http://127.0.0.1:3381/v1/userDataByFid?fid=<you>'
curl 'http://127.0.0.1:3381/v1/linksByFid?fid=<you>&link_type=follow'
curl 'http://127.0.0.1:3381/v1/reactionsByCast?target_fid=<them>&target_hash=0x…&reaction_type=Like'

Common parameters: pageSize, pageToken, reverse=true, and startTimestamp / stopTimestamp on the endpoints that support them. Paging is token-based — follow nextPageToken until it is empty.

Writes are built, signed with the app key, serialized, and POSTed as raw protobuf bytes:

curl -X POST http://127.0.0.1:3381/v1/submitMessage \
  -H 'content-type: application/octet-stream' \
  --data-binary @message.encoded.protobuf

Message.encode(msg).finish() produces those bytes. Note the content type: the endpoint does not accept JSON.

Step 4 — include or exclude casts by client

Farcaster does not put a client name in a message, so how do you tell which app posted a cast?

Through the app key that signed it. Every cast is signed by an app key, and every gasless app key carries a requestFid — the FID of the app that requested it, taken from the SignedKeyRequest metadata that was verified when the key was registered.

So: cast.signer → the author's key list → requestFid → which client.

curl 'http://127.0.0.1:3381/v1/signersByFid?fid=<author>' | jq '.signers[] | {key, requestFid, scopes, expiresAt}'

The client resolves this for every author in your feed and labels each cast. Then "only show my client" and "hide that client" are simple filters on requestFid.

Two limits:

• Keys registered the old way, onchain, have no SignedKeyRequest metadata and therefore no requestFid. They can only be identified by their key. The client falls back to showing key:0x… for those.
• None of this is proof that a human used an app. It says which app's key signed the message, which is the strongest claim the protocol actually supports.

Seed phrase safety

The client asks for your seed phrase once, to authorize its app key. Know what you are handing over before you paste it.

The seed phrase derives your custody address, and the custody address owns your FID. Whoever has the phrase can transfer the FID, change its recovery address, and add or revoke any key. Nobody can undo that for you.

So:

• Use a test account for this tutorial. See Before you start, or use an account you would not mind losing. Do not paste your main account's seed phrase into anything while following a tutorial.
• Only paste a seed phrase into software from developers you trust — and, ideally, software you can inspect. This client is open source, and the part that touches the seed is a few dozen lines.
• Prefer delegated signer authorization. This client uses the seed phrase to sign one delegation: an app key that is scoped (it cannot add other keys), expires after 30 days unused, and can be revoked with a KEY_REMOVE. Posting, following and reacting use only that key. The seed phrase is needed again only if you revoke the key from the client.
• Never paste a seed phrase into a web page you did not start yourself. This client binds to 127.0.0.1 by default for exactly that reason. If you pass --bind 0.0.0.0, you have published your seed phrase input box to your network.
• Revoke keys you are done with. Deleting the signer file does not revoke the key: anyone with a copy can keep using it, and each use extends its life. Revoke it from the client, which sends a KEY_REMOVE. A key nobody uses expires after 30 days.

Troubleshooting

up has been running for hours. Expected on first run. The snapshot is several hundred GB. readnode status shows the countdown; blockDelay in single digits means done.

The node died mid-sync, disk full. You used a 1 TB disk. The snapshot scratch directory needs room for a second copy. Use 2 TB.

KEY_ADD rejected for its nonce (nonce is not greater than stored nonce). Another KEY_ADD or KEY_REMOVE landed first. Re-read currentUserNonce and submit a higher value. Never retry with the same nonce.

KEY_ADD rejected for its signature. The KeyAdd signature did not recover the FID's custody address. Check that the seed phrase you imported derives to the address that idOf() returns.

KEY_ADD rejected for its metadata. Your metadata may have used the onchain SignedKeyRequestValidator domain. Build it with makeKeyAddBody(), which signs the off-chain domain.

KEY_ADD rejected for its scopes. KEY_ADD and KEY_REMOVE can never be scopes. Anything outside the admissible set is rejected.

mempoolSize is 4294967295. Normal on a read node. It means "not reported".

The cast was accepted but never appeared. You got validation, not inclusion. On a read node, the message depends on gossip reaching a validator. Submit again, or restart the client with --submit-url pointing at a validator for a stronger guarantee.

Writes rejected for storage. The FID has no storage rented. Check /v1/storageLimitsByFid. Storage is rented onchain; this tool does not rent it.

A subscriber missed events. Events are pruned after 3 days by default (pruning.event_retention). A subscriber resuming from an event id older than the retention window gets nothing and must backfill from the message APIs.

Cost

For a one-week run on AWS m5.xlarge + 2 TB gp3:

Storage is billed by the calendar, not by usage, so it dominates and it keeps charging while the instance is stopped. Let it run a full month and the volume alone is $164. Delete the volume when you are done.

Cheaper shapes for a short run:

• GCP — the same machine with pd-standard at $0.04/GB-month instead of $0.08. About $52 for the week.
• Spot EC2 — roughly $0.07/hr, but interruption risk. Survivable here only because the database lives on EBS, not on instance store.
• Run it for three days instead of seven — about $30. Sync takes hours, not days, so the node does not need to exist all week.

The number to watch is the disk, not the CPU.

Where the official docs drift

Two things were out of date while this was written, and both are corrected above:

1. snapchain.farcaster.xyz/guides/writing-messages notes that its linked hello-world example still registers its signer onchain via the key gateway. The gasless flow in that guide's step 3 replaces it and needs no ETH.
2. GetOnChainSignersByFid returns onchain keys only. Use GetSignersByFid / GET /v1/signersByFid, which returns both kinds in one list, plus currentUserNonce and the per-FID gasless limits.

Point 1 is a live example in farcasterxyz/hub-monorepo. If you are reading this and it still applies, a pull request is welcome — that repository is the canonical place for it.

References

The four sources the bounty cites, plus the two pages that superseded parts of them. Read these when this tutorial and reality disagree.

1. Farcaster architecture overview — the two systems: onchain registries on Optimism, messages on Snapchain.
2. Hello world — the canonical first client. It still registers its signer onchain; see Where the official docs drift.
3. Running a Snapchain node — hardware, ports and the official install script that readnode up wraps.
4. Snapchain HTTP API — every /v1/ endpoint the client calls.
5. Node types — read nodes vs validators, and why a read node relays writes.
6. Writing messages — the gasless KEY_ADD flow used in Part 3.