# Errors and limits > Error messages, error codes, and usage limits for HyperCore WebSocket streams. > For the complete documentation index, see [llms.txt](/docs/llms.txt). HyperCore APIs are in beta. Message fields, limits, and behavior may change, including breaking changes. To request access, contact [abdul.manan@alchemy.com](mailto:abdul.manan@alchemy.com). # Errors and limits ## Error messages Request errors arrive in one of two shapes: **Subscription error**: the request was understood and rejected. It carries the `subscriptionId` you sent. ```json {"channel":"subscriptionResponse","subscriptionId":"l2_01","error":{"code":"invalid_params","message":"nLevels must be one of 1, 10, 20, 50; got 7"}} ``` **Connection-level error**: no `subscriptionId`. Sent when a request can't be parsed, even if it included a `subscriptionId`. ```json {"channel":"error","error":{"code":"invalid_params","message":"missing field `subscriptionId`"}} ``` `book_reset` is different: it isn't a request failure. It arrives on the stream's own channel with your `subscriptionId` and the next `seq`, the subscription stays open, and a snapshot follows: ```json {"seq":42,"channel":"l2BookDiff","subscriptionId":"diff_01","error":{"code":"book_reset","message":"book reseeding"}} ``` Which shape you get depends on where the request fails: * **Connection-level**: the message isn't valid JSON, `method` is missing or unknown, `subscriptionId` is missing, `type` is missing or unknown, a required field is missing (for example `users` on `userFills`), or a value has the wrong type (for example `"fromBlock":"abc"`). * **Subscription error**: the request parsed but a value is out of range or over a limit, for example `nLevels`, `nSigFigs`, an empty or oversized `users` list, too many `coins`, or a duplicate subscription. Because connection-level errors don't name a subscription, send subscribe requests one at a time, or match each acknowledgement to its request, if you need to know which one failed. Successful subscribe and unsubscribe requests are both acknowledged with `channel: "subscriptionResponse"` and a `data` object that echoes the subscription. A response with `error` instead of `data` is a failure. Branch on `error.code`. Message text is for humans and may change. ## Error codes | Code | Meaning | What to do | | --- | --- | --- | | `invalid_params` | The request is malformed or a parameter is out of range. Also returned when you unsubscribe an ID that isn't active. | Fix the request. The message describes the problem. | | `already_exists` | The `subscriptionId` is already in use on this connection, or this connection already has a subscription with the same type and filters under another ID. | Use a different ID, change the filters, or unsubscribe first. | | `limit_reached` | A usage limit was hit, such as too many subscriptions on the connection, too many `users`, `builders` or `coins`, or a second unfiltered subscription of the same type. | See [limits](#limits). | | `book_reset` | A book was re-seeded internally. The subscription stays open and the next data message is a snapshot. | Drop local state for that subscription and rebuild from the snapshot. | | `fills_not_ready`, `book_not_ready` | Temporary internal unavailability. | Retry the subscription after a short delay. | | `going_away` | The server is shutting down for a deployment. New subscriptions are refused; the connection closes shortly with code `1001`. | Reconnect with backoff. | New codes may be added. Treat unknown codes as errors for the affected subscription. ## Limits Limits protect shared infrastructure and may change during early access. Hitting a limit on a subscription returns `limit_reached`; existing subscriptions keep working. | Limit | Value | | --- | --- | | Subscriptions per connection | 200 | | Addresses in `users` or `builders` | 1 to 200 per subscription | | Markets in `coins` | Up to 200 per subscription | | Unfiltered subscriptions per stream type | 1 per connection, 5 per team (`liquidationFills`: see below) | | Subscriptions per team | 20,000 | | Concurrent connections per team | 1,000 | | Request message size | 256 KiB | | `subscriptionId` and coin name length | 128 characters each | A connection over your team's connection limit is refused during the handshake with HTTP `429`; the server may also refuse with HTTP `503` when it's at capacity. Reconnect with backoff in both cases. Contact [abdul.manan@alchemy.com](mailto:abdul.manan@alchemy.com) if you need higher limits. A request larger than 256 KiB closes the connection with code `1009`. ### Unfiltered subscriptions Omitting `coins`, or sending an empty list (`"coins":[]`), subscribes to every market. `liquidationFills` has no `coins` filter, so every `liquidationFills` subscription is unfiltered; a connection can hold one with `aggregateByTime` on and one with it off. Unfiltered book streams carry a lot of data: | Stream (all markets) | Approximate volume | | --- | --- | | `l2Book` | ~2–3 MB/s | | `l4BookUpdates` | ~1.3–1.7 MB/s, plus a first message of about 75 MB | | `l2BookDiff` | ~0.35–0.45 MB/s | | `bbo`, `allFills` | under 0.1 MB/s | Volumes vary with market activity. Usage is metered by data delivered, so filter by `coins` where you can. For a live book, `l2BookDiff` carries the same information as `l2Book` at a fraction of the volume. ## Input rules * Fields the server doesn't recognize are ignored rather than rejected. A misspelled or unsupported field, such as `coin` instead of `coins` or `marketTypes`, is dropped, and dropping a filter can turn the request into an unfiltered, all-markets subscription. The acknowledgement echoes the filters that were applied, so check it. * Coin names are case-sensitive and must match Hyperliquid's names exactly. An unknown coin is accepted: book streams return it with empty data (for example `"bbo":[null,null]`) until that market exists, so check spelling. Duplicate coins are ignored. See [markets and coin names](/docs/data/hypercore/concepts/markets-assets-and-dexes). * Addresses are case-insensitive and are returned lowercase. Duplicates are ignored. * `subscriptionId` must be 1 to 128 characters with no control characters.