# Swap by reply on Farcaster and X

> Mention @layerhop with "swap 10 USDC to SOL" in a cast or post and get a link to a prefilled swap. On Farcaster it opens as a Mini App with your Farcaster wallet. The bots never execute swaps.

Source: https://docs.layerhop.com/guides/swap-by-reply

Write a cast on Farcaster or a post on X that mentions LayerHop's account with a swap request:

```text
@layerhop swap 10 USDC to SOL
```

The bot replies with a link to a prefilled swap page at `app.layerhop.com/swap`. You check the live quote, change anything you like, connect your own wallet and sign. **The bots never quote on your behalf, hold funds, sign or send anything**: the reply is only a link.

## What can I write?

The parser (`parseSwapCommand` in `@layerhop/shared`) understands:

| You write | It means |
| --- | --- |
| `swap 10 USDC to SOL` | 10 USDC (on Base, which the reply says you can change) to SOL on Solana |
| `swap 100 USDC on Arbitrum to USDT on Polygon` | both chains named |
| `bridge 0.1 ETH from Arbitrum to Base` | a chain name as the destination coin: ETH on Base |
| `swap 0.5 SOL to USDC` | SOL names Solana, so USDC arrives on Solana too |
| `swap 0.1 ETH to USDC on Base` | a chain named only at the end applies to both sides |
| `buy $10 of SOL`, `buy SOL with 10 USDC` | buy with USDC |
| `25 usdc → sol` | no verb needed when the request is complete |

- **Amounts**: `10`, `0.5`, `1,000`, `2.5k`, `$10` (dollars, only with a stablecoin). `max`, `all` or `half` get a question back: the bot never guesses an amount.
- **Tokens**: symbols in any case, `$SOL` tickers, `usd`/`dollars` (USDC), `ether`, `matic` (POL), or a token address with its chain (`to 0x4ed4…efed on base`; a Solana mint implies Solana).
- **Chains**: slug, name or id, plus `eth`/`mainnet`, `arb`, `op`, `bnb`/`bsc`, `poly`/`matic`, `sol`, `avax`. Coins that live on one chain (SOL, BNB, POL, AVAX, …) name their chain; ETH and stablecoins don't.
- **Ambiguity gets a question**, not a guess: `swap 10 USDC to ETH` asks which chain ETH should arrive on. A misspelt chain (`on bsae`) is pointed out.
- Chat that merely mentions an amount ("I sent 10 USDC to my friend") and `send … to <address>` get no reply.

## How does the Farcaster Mini App work?

Every prefilled swap link on `app.layerhop.com/swap` carries a [Farcaster Mini App](https://miniapps.farcaster.xyz) embed (`fc:miniapp`, plus the legacy `fc:frame`) with an image of the live quote and a **Swap on LayerHop** button. In a Farcaster client the button opens the page inside the client, and the page connects the client's own wallet (the EIP-1193 provider from the Mini App SDK). You still review and sign the swap. The manifest is at `app.layerhop.com/.well-known/farcaster.json`.

You can post such links yourself: any [deep link](/guides/deep-links) to `app.layerhop.com/swap?…` unfurls the same way on Farcaster, and as an image of the quote on X, Telegram and Discord.

## How is the Farcaster bot built?

Neynar delivers casts that mention the bot to `POST /v1/social/farcaster/webhook` (`cast.created`). Each delivery is signed: `X-Neynar-Signature` is the HMAC-SHA512 (hex) of the raw body with the webhook secret, and unsigned or mis-signed requests get `401`. The bot replies through Neynar's cast API with the swap link as an embed, once per cast (a retry is recognised), at most 5 replies per author and hour and `FARCASTER_MAX_REPLIES_PER_DAY` a day.

## How is the X bot built?

It polls the bot account's mentions (`GET /2/users/{id}/mentions`, app bearer token) every `X_POLL_SECONDS` and replies with `POST /2/tweets` using the account's OAuth 1.0a user tokens. Every mention read and every reply is recorded, so the monthly spend estimate survives restarts. It pauses for the month at `X_MONTHLY_BUDGET_USD`, posts at most `X_MAX_REPLIES_PER_DAY` replies and 3 per author a day, and answers each post once. X bills link posts at a much higher rate than plain posts, so keep the daily cap low.

Both bots are off unless their credentials are set; see the deployment guide in the repository (`docs/DEPLOY.md`) for the variables and the cost notes.