# Builder fills | API reference | Femtos

> Every fill of one builder code, with its builder fee, oid, tid and hash. GET /v1/hypercore/builders/{builder}/fills on HyperCore: parameters, response fields and a live call per layer.

- Base URL: `https://api.femtos.xyz/v1` (REST) · `wss://api.femtos.xyz/v1/ws` (WebSocket) · MCP: `https://api.femtos.xyz/mcp`
- Auth: `Authorization: Bearer $FEMTOS_KEY`. Free key: https://dashboard.femtos.xyz/signup (browser), or with
  no browser: `GET https://femtos.xyz/accounts/agent/challenge`, solve its proof of work, then `POST https://femtos.xyz/accounts/agent/signup`
  (https://femtos.xyz/agents.md#agent-onboarding)
- Decimals are exact strings, times Unix milliseconds, addresses lowercase `0x`
- Whole API in one file: https://femtos.xyz/agents.md · OpenAPI: https://api.femtos.xyz/v1/openapi.json · Index: https://femtos.xyz/llms.txt
- Page with live calls: https://femtos.xyz/reference/builder-fills

## Builder fills — GET `/v1/hypercore/builders/{builder}/fills`

Every fill of one builder code, with its builder fee, oid, tid and hash.

Layers: HyperCore. Not on Elysium or HyperEVM: served on HyperCore only.
Page with live calls: https://femtos.xyz/reference/builder-fills?layer=hypercore

| Param | In | Example or values | Meaning |
|---|---|---|---|
| `builder` | path | `0xb84168cf3be63c6b8dad05ff5d755e97432ff80b` | Builder address (0x), as orders name it in `builder.b` |
| `from` | query | (optional) | Window start (Unix ms, default to − 24 h) |
| `to` | query | (optional) | Window end (Unix ms, exclusive, default now) |
| `coin` | query | (optional) | One market |
| `user` | query | (optional) | One account |
| `limit` | query | `20` | Rows |
| `cursor` | query | (optional) | Next page: `next_cursor` of the previous answer |

```bash
curl -H "Authorization: Bearer $FEMTOS_KEY" "https://api.femtos.xyz/v1/hypercore/builders/0xb84168cf3be63c6b8dad05ff5d755e97432ff80b/fills?limit=20"
```

| Field | Type | Meaning |
|---|---|---|
| `fills[]` | object | Newest first: {block, eventIdx, time, user, entity, coin, side, px, sz, notional, crossed, dir, …} |
| `fills[].builderFee` | decimal | Builder fee of the fill, in feeToken |
| `fills[].notional` | decimal | px × sz, quote units |
| `from` | ms | Window start read |
| `to` | ms | Window end |
| `next_cursor` | string \| null | Opaque cursor of the next page: pass it as `cursor`, unchanged. null on the last page |
| `billing` | medium | medium |

Next page: `cursor` = the `next_cursor` of the previous answer (https://femtos.xyz/agents.md#pagination).

## Related (Builder codes)

- [Builder leaderboard](https://femtos.xyz/reference/builders.md) `GET /v1/hypercore/builders`: Every builder code ranked by fees, volume, users or orders, over 24 h to all time. (HyperCore)
- [Builder](https://femtos.xyz/reference/builder.md) `GET /v1/hypercore/builders/{builder}`: One builder code: totals and rank, day by day, per market, order outcomes and fee rates. (HyperCore)
- [Builder orders](https://femtos.xyz/reference/builder-orders.md) `GET /v1/hypercore/builders/{builder}/orders`: Every status of the orders sent with one builder code, rejections and their reasons included. (HyperCore)
- [Builder orders stream](https://femtos.xyz/reference/ws/builder-orders.md) `WS hc.builder.orders`: Every status of the orders sent with one builder code as it happens, rejections and their reasons included. One frame per block with all its matching events. (HyperCore)
- [Builder fills stream](https://femtos.xyz/reference/ws/builder-fills.md) `WS hc.builder.fills`: Every fill of one builder code as it happens, with its builder fee: the rows of the builder fills route, pushed per block. One frame per block with all its matching events. (HyperCore)

Every page: https://femtos.xyz/reference.md