Guide - TON Center

Client

Pass these parameters when creating ToncenterRestClient:

Parameter	Default	Description
`api_key`	Optional	API key or list of keys for rotation.
`network`	Mainnet	Mainnet or Testnet.
`base_url`	Optional	Custom base URL (overrides network selection).
`timeout`	10 seconds	Request timeout.
`session`	Optional	External HTTP session to share across clients.
`headers`	Optional	Extra HTTP headers sent with every request.
`cookies`	Optional	Extra cookies sent with every request.
`rps_limit`	Optional	Client-side rate limit (requests per second).
`rps_period`	Optional	Rate-limiter window in seconds.
`retry_policy`	Enabled	Retry policy. Disable by passing None.

Without an API key the SDK auto-limits to 1 RPS / 1.2 s on the client side to match the server-side throttle. With a key, client-side limiting is off unless set explicitly.

Session

Context manager
Manual
External

from toncenter.rest import ToncenterRestClient
from toncenter.types import Network

async with ToncenterRestClient(network=Network.MAINNET) as client:
    balance = await client.v2.accounts.get_address_balance("EQDtFpEwcFAEcRe5mLVh2N6C0x-_hJEM7W61_JLnSF74p4q2")

from toncenter.rest import ToncenterRestClient
from toncenter.types import Network

client = ToncenterRestClient(network=Network.MAINNET)
await client.create_session()
try:
    balance = await client.v2.accounts.get_address_balance("EQDtFpEwcFAEcRe5mLVh2N6C0x-_hJEM7W61_JLnSF74p4q2")
finally:
    await client.close_session()

import aiohttp

from toncenter.rest import ToncenterRestClient
from toncenter.types import Network

async with aiohttp.ClientSession() as session:
    async with ToncenterRestClient(
        network=Network.MAINNET,
        session=session,
    ) as client:
        balance = await client.v2.accounts.get_address_balance("EQDtFpEwcFAEcRe5mLVh2N6C0x-_hJEM7W61_JLnSF74p4q2")

The client does not close an external session — you manage its lifecycle yourself.

Retries

Rate-limited (429) and server-error responses are retried automatically with exponential backoff.

Status codes	Max retries	Base delay	Max delay	Backoff
429	5	0.3 s	3 s	2x
500, 502, 503, 504	3	0.5 s	5 s	2x

Custom policy:

from toncenter.types import RetryPolicy, RetryRule

client = ToncenterRestClient(
    network=Network.MAINNET,
    retry_policy=RetryPolicy(rules=(
        RetryRule(
            statuses=frozenset({429}),
            max_retries=10,
            base_delay=0.5,
            max_delay=10.0,
            backoff_factor=2.0,
        ),
    )),
)

Field	Default	Description
`statuses`	Required	HTTP status codes that trigger retry.
`max_retries`	3	Maximum retry attempts.
`base_delay`	1 second	Initial delay.
`max_delay`	30 seconds	Upper bound after backoff.
`backoff_factor`	2.0	Multiplier per attempt.

The defaults above apply when creating a custom RetryRule. The SDK’s built-in policy uses tuned values shown in the table above.

Pass retry_policy=None to disable retries entirely.

Key Rotation

Pass a list of ApiKey objects to rotate between keys on rate-limit errors (429). Each key carries its own client-side rate limit.

from toncenter.types import ApiKey

client = ToncenterRestClient(
    api_key=[
        ApiKey("free-key", rps_limit=10),
        ApiKey("plus-key", rps_limit=25),
    ],
    network=Network.MAINNET,
)

A single ApiKey also works — rate limit is taken from the object instead of the constructor rps_limit parameter:

client = ToncenterRestClient(api_key=ApiKey("my-key", rps_limit=10))

On 429, the SDK exhausts all retry attempts for the current key (with backoff), then rotates to the next key and retries with a fresh cycle. Each key uses its own RateLimiter.

​Client

​Session

​Retries

​Key Rotation

Client

Session

Retries

Key Rotation