simulateTransaction

curl --fail-with-body -s https://rpc-testnet.lumeus.dev \
  -H "Authorization: Bearer $LUMEUS_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"simulateTransaction","params":{"transaction":"AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA="}}'

// Node 18+. Save as rpc.mjs and run: node rpc.mjs
const rpc = async (method, params) => {
  const res = await fetch('https://rpc-testnet.lumeus.dev', {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.LUMEUS_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ jsonrpc: '2.0', id: 1, method, params }),
  });
  const body = await res.json();
  if (body.error) throw new Error(`${body.error.data ?? body.error.code}: ${body.error.message}`);
  return body.result;
};

console.log(JSON.stringify(await rpc('simulateTransaction', { transaction: 'AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=' }), null, 2));

import json
import os

import requests


def rpc(method, params=None):
    body = {"jsonrpc": "2.0", "id": 1, "method": method}
    if params is not None:
        body["params"] = params
    res = requests.post(
        "https://rpc-testnet.lumeus.dev",
        json=body,
        headers={"Authorization": f"Bearer {os.environ['LUMEUS_API_KEY']}"},
        timeout=30,
    )
    data = res.json()
    if "error" in data:
        raise RuntimeError(f"{data['error'].get('data')}: {data['error']['message']}")
    return data["result"]


print(json.dumps(rpc("simulateTransaction", {"transaction": "AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA="}), indent=2))

// npm install @stellar/stellar-sdk. Save as sdk.mjs and run: node sdk.mjs
import { Networks, TransactionBuilder, rpc, scValToNative } from '@stellar/stellar-sdk';

const server = new rpc.Server('https://rpc-testnet.lumeus.dev', {
  headers: { Authorization: `Bearer ${process.env.LUMEUS_API_KEY}` },
});

// An unsigned transaction that calls balance(GAIH…) on the native XLM contract.
// Build your own with TransactionBuilder; see /rpc/transactions.
const tx = TransactionBuilder.fromXDR(
  'AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=',
  Networks.TESTNET,
);
const sim = await server.simulateTransaction(tx);
if (rpc.Api.isSimulationError(sim)) throw new Error(sim.error);
console.log(JSON.stringify({
  latestLedger: sim.latestLedger,
  minResourceFee: sim.minResourceFee,
  returnValue: scValToNative(sim.result.retval), // the i128 balance in stroops
}, (k, v) => (typeof v === 'bigint' ? v.toString() : v), 2));

# pip install stellar-sdk
import os

from stellar_sdk import Network, SorobanServer, TransactionEnvelope
from stellar_sdk.client.requests_client import RequestsClient

# num_retries=0: raise 429/503 at once instead of sleeping through Retry-After.
server = SorobanServer(
    "https://rpc-testnet.lumeus.dev",
    client=RequestsClient(num_retries=0, custom_headers={"Authorization": f"Bearer {os.environ['LUMEUS_API_KEY']}"}),
)

# An unsigned transaction that calls balance(GAIH…) on the native XLM contract.
tx = TransactionEnvelope.from_xdr(
    "AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=",
    Network.TESTNET_NETWORK_PASSPHRASE,
)
print(server.simulate_transaction(tx).model_dump_json(by_alias=True, indent=2))

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "transactionData": "AAAAAAAAAAIAAAAAAAAAABB90WssODNIgi6BHveqzxTRmIpvAFRyVNM+Hm2GVuCcAAAABgAAAAHXkotywnA8z+r365/0701QSlWouXn8m0UOoshCtNHOYQAAABQAAAABAAAAAAACKrwAAACQAAAAAAAAAAAAABv+",
    "events": [
      "AAAAAQAAAAAAAAAAAAAAAgAAAAAAAAADAAAADwAAAAdmbl9jYWxsAAAAAA0AAAAg15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAPAAAAB2JhbGFuY2UAAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4Jw=",
      "AAAAAQAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAACAAAAAAAAAAIAAAAPAAAACWZuX3JldHVybgAAAAAAAA8AAAAHYmFsYW5jZQAAAAAKAAAAAAAAAAAA+uvGAeHukA=="
    ],
    "minResourceFee": "7166",
    "results": [
      {
        "auth": [],
        "xdr": "AAAACgAAAAAAAAAAAPrrxgHh7pA="
      }
    ],
    "latestLedger": 5331531
  }
}

POST

curl --fail-with-body -s https://rpc-testnet.lumeus.dev \
  -H "Authorization: Bearer $LUMEUS_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"simulateTransaction","params":{"transaction":"AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA="}}'

// Node 18+. Save as rpc.mjs and run: node rpc.mjs
const rpc = async (method, params) => {
  const res = await fetch('https://rpc-testnet.lumeus.dev', {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.LUMEUS_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ jsonrpc: '2.0', id: 1, method, params }),
  });
  const body = await res.json();
  if (body.error) throw new Error(`${body.error.data ?? body.error.code}: ${body.error.message}`);
  return body.result;
};

console.log(JSON.stringify(await rpc('simulateTransaction', { transaction: 'AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=' }), null, 2));

import json
import os

import requests


def rpc(method, params=None):
    body = {"jsonrpc": "2.0", "id": 1, "method": method}
    if params is not None:
        body["params"] = params
    res = requests.post(
        "https://rpc-testnet.lumeus.dev",
        json=body,
        headers={"Authorization": f"Bearer {os.environ['LUMEUS_API_KEY']}"},
        timeout=30,
    )
    data = res.json()
    if "error" in data:
        raise RuntimeError(f"{data['error'].get('data')}: {data['error']['message']}")
    return data["result"]


print(json.dumps(rpc("simulateTransaction", {"transaction": "AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA="}), indent=2))

// npm install @stellar/stellar-sdk. Save as sdk.mjs and run: node sdk.mjs
import { Networks, TransactionBuilder, rpc, scValToNative } from '@stellar/stellar-sdk';

const server = new rpc.Server('https://rpc-testnet.lumeus.dev', {
  headers: { Authorization: `Bearer ${process.env.LUMEUS_API_KEY}` },
});

// An unsigned transaction that calls balance(GAIH…) on the native XLM contract.
// Build your own with TransactionBuilder; see /rpc/transactions.
const tx = TransactionBuilder.fromXDR(
  'AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=',
  Networks.TESTNET,
);
const sim = await server.simulateTransaction(tx);
if (rpc.Api.isSimulationError(sim)) throw new Error(sim.error);
console.log(JSON.stringify({
  latestLedger: sim.latestLedger,
  minResourceFee: sim.minResourceFee,
  returnValue: scValToNative(sim.result.retval), // the i128 balance in stroops
}, (k, v) => (typeof v === 'bigint' ? v.toString() : v), 2));

# pip install stellar-sdk
import os

from stellar_sdk import Network, SorobanServer, TransactionEnvelope
from stellar_sdk.client.requests_client import RequestsClient

# num_retries=0: raise 429/503 at once instead of sleeping through Retry-After.
server = SorobanServer(
    "https://rpc-testnet.lumeus.dev",
    client=RequestsClient(num_retries=0, custom_headers={"Authorization": f"Bearer {os.environ['LUMEUS_API_KEY']}"}),
)

# An unsigned transaction that calls balance(GAIH…) on the native XLM contract.
tx = TransactionEnvelope.from_xdr(
    "AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=",
    Network.TESTNET_NETWORK_PASSPHRASE,
)
print(server.simulate_transaction(tx).model_dump_json(by_alias=True, indent=2))

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "transactionData": "AAAAAAAAAAIAAAAAAAAAABB90WssODNIgi6BHveqzxTRmIpvAFRyVNM+Hm2GVuCcAAAABgAAAAHXkotywnA8z+r365/0701QSlWouXn8m0UOoshCtNHOYQAAABQAAAABAAAAAAACKrwAAACQAAAAAAAAAAAAABv+",
    "events": [
      "AAAAAQAAAAAAAAAAAAAAAgAAAAAAAAADAAAADwAAAAdmbl9jYWxsAAAAAA0AAAAg15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAPAAAAB2JhbGFuY2UAAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4Jw=",
      "AAAAAQAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAACAAAAAAAAAAIAAAAPAAAACWZuX3JldHVybgAAAAAAAA8AAAAHYmFsYW5jZQAAAAAKAAAAAAAAAAAA+uvGAeHukA=="
    ],
    "minResourceFee": "7166",
    "results": [
      {
        "auth": [],
        "xdr": "AAAACgAAAAAAAAAAAPrrxgHh7pA="
      }
    ],
    "latestLedger": 5331531
  }
}

Runs a transaction against the current ledger without submitting it and returns its return value, footprint (transactionData), minimum resource fee, events and the authorization it needs. The transaction does not need to be signed and its sequence number is not checked. The example calls balance on the native XLM contract for the sample Testnet account; SDKs build this envelope for you (prepareTransaction in JavaScript). The examples call Testnet with your key in LUMEUS_API_KEY; the SDK tabs use @stellar/stellar-sdk and the Python stellar-sdk (SDK setup and errors). On Mainnet, use https://rpc.lumeus.dev and a lum_live_ key.

curl --fail-with-body -s https://rpc-testnet.lumeus.dev \
  -H "Authorization: Bearer $LUMEUS_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"simulateTransaction","params":{"transaction":"AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA="}}'

// Node 18+. Save as rpc.mjs and run: node rpc.mjs
const rpc = async (method, params) => {
  const res = await fetch('https://rpc-testnet.lumeus.dev', {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.LUMEUS_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ jsonrpc: '2.0', id: 1, method, params }),
  });
  const body = await res.json();
  if (body.error) throw new Error(`${body.error.data ?? body.error.code}: ${body.error.message}`);
  return body.result;
};

console.log(JSON.stringify(await rpc('simulateTransaction', { transaction: 'AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=' }), null, 2));

import json
import os

import requests


def rpc(method, params=None):
    body = {"jsonrpc": "2.0", "id": 1, "method": method}
    if params is not None:
        body["params"] = params
    res = requests.post(
        "https://rpc-testnet.lumeus.dev",
        json=body,
        headers={"Authorization": f"Bearer {os.environ['LUMEUS_API_KEY']}"},
        timeout=30,
    )
    data = res.json()
    if "error" in data:
        raise RuntimeError(f"{data['error'].get('data')}: {data['error']['message']}")
    return data["result"]


print(json.dumps(rpc("simulateTransaction", {"transaction": "AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA="}), indent=2))

// npm install @stellar/stellar-sdk. Save as sdk.mjs and run: node sdk.mjs
import { Networks, TransactionBuilder, rpc, scValToNative } from '@stellar/stellar-sdk';

const server = new rpc.Server('https://rpc-testnet.lumeus.dev', {
  headers: { Authorization: `Bearer ${process.env.LUMEUS_API_KEY}` },
});

// An unsigned transaction that calls balance(GAIH…) on the native XLM contract.
// Build your own with TransactionBuilder; see /rpc/transactions.
const tx = TransactionBuilder.fromXDR(
  'AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=',
  Networks.TESTNET,
);
const sim = await server.simulateTransaction(tx);
if (rpc.Api.isSimulationError(sim)) throw new Error(sim.error);
console.log(JSON.stringify({
  latestLedger: sim.latestLedger,
  minResourceFee: sim.minResourceFee,
  returnValue: scValToNative(sim.result.retval), // the i128 balance in stroops
}, (k, v) => (typeof v === 'bigint' ? v.toString() : v), 2));

# pip install stellar-sdk
import os

from stellar_sdk import Network, SorobanServer, TransactionEnvelope
from stellar_sdk.client.requests_client import RequestsClient

# num_retries=0: raise 429/503 at once instead of sleeping through Retry-After.
server = SorobanServer(
    "https://rpc-testnet.lumeus.dev",
    client=RequestsClient(num_retries=0, custom_headers={"Authorization": f"Bearer {os.environ['LUMEUS_API_KEY']}"}),
)

# An unsigned transaction that calls balance(GAIH…) on the native XLM contract.
tx = TransactionEnvelope.from_xdr(
    "AAAAAgAAAAAQfdFrLDgzSIIugR73qs8U0ZiKbwBUclTTPh5thlbgnAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAGAAAAAAAAAAB15KLcsJwPM/q9+uf9O9NUEpVqLl5/JtFDqLIQrTRzmEAAAAHYmFsYW5jZQAAAAABAAAAEgAAAAAAAAAAEH3Rayw4M0iCLoEe96rPFNGYim8AVHJU0z4ebYZW4JwAAAAAAAAAAAAAAAA=",
    Network.TESTNET_NETWORK_PASSPHRASE,
)
print(server.simulate_transaction(tx).model_dump_json(by_alias=True, indent=2))

Result

The fields of result (stellar-rpc 29). Fields marked “Present only when it applies” can be absent.

Field	Type	Description
`error`	string	Only when simulation failed: why. The other fields are then mostly absent.
`transactionData`	string	SorobanTransactionData to set on the transaction. Base64 XDR (with xdrFormat json, the matching Json field instead). Present only when it applies.
`transactionDataJson`	JSON	SorobanTransactionData. Decoded JSON; only with xdrFormat json.
`events`	string[]	Base64 DiagnosticEvent XDR. Present only when it applies.
`eventsJson`	JSON[]	Decoded diagnostic events; only with xdrFormat json.
`minResourceFee`	string	Minimum resource fee in stroops, as a string. Present only when it applies.
`results`	object[]	One result per host function call. Present only when it applies.
`results[].auth`	string[]	Base64 SorobanAuthorizationEntry XDR the call needs. Present only when it applies.
`results[].authJson`	JSON[]	Decoded authorization entries; only with xdrFormat json.
`results[].xdr`	string	Base64 ScVal XDR return value. Present only when it applies.
`results[].returnValueJson`	JSON	Return value. Decoded JSON; only with xdrFormat json.
`restorePreamble`	object	Only when archived entries must be restored first: submit a RestoreFootprint transaction with this data.
`restorePreamble.transactionData`	string	SorobanTransactionData of the restore. Base64 XDR (with xdrFormat json, the matching Json field instead). Present only when it applies.
`restorePreamble.transactionDataJson`	JSON	SorobanTransactionData. Decoded JSON; only with xdrFormat json.
`restorePreamble.minResourceFee`	string	Resource fee of the restore, as a string.
`stateChanges`	object[]	How ledger entries would change. Present only when it applies.
`stateChanges[].type`	string	One of `created`, `updated`, `deleted`.
`stateChanges[].key`	string	Base64 LedgerKey XDR. Present only when it applies.
`stateChanges[].keyJson`	JSON	LedgerKey. Decoded JSON; only with xdrFormat json.
`stateChanges[].before`	string or null	Base64 LedgerEntry XDR before; null when created.
`stateChanges[].beforeJson`	JSON	LedgerEntry before. Decoded JSON; only with xdrFormat json.
`stateChanges[].after`	string or null	Base64 LedgerEntry XDR after; null when deleted.
`stateChanges[].afterJson`	JSON	LedgerEntry after. Decoded JSON; only with xdrFormat json.
`latestLedger`	integer	Ledger the simulation ran against.

Parameters

Name	Type	Rules
`transaction`	string	Required. Base64 TransactionEnvelope XDR with one InvokeHostFunction, ExtendFootprintTTL or RestoreFootprint operation.
`resourceConfig.instructionLeeway`	integer	Extra CPU instructions to add to the estimate.
`authMode`	string	`enforce`, `record` or `record_allow_nonroot`.
`xdrFormat`	string	`base64` (default) or `json`.

Credits and limits

Mainnet: 5 credits plus 1 credit per started 64 KiB of response, so a small answer costs 6 credits. A call that returns a JSON-RPC error costs nothing.
Testnet: free. Each call counts toward your organization’s 10,000 Testnet requests a day; above that, calls get 429 rate_limited until 00:00 UTC.
Response ceiling 8 MiB. A simulation that returns result.error is still charged its 5 credits. Publishable keys cannot call it.
The plan RPC rate applies per call; each call in a batch counts as one.

Errors

Gateway errors are JSON-RPC errors with the machine code in error.data and the request ID in error.request_id. Common ones: -32602 (invalid_request, HTTP 400) for invalid params, -32000 with unauthorized (401), rate_limited (429, wait Retry-After seconds) or unavailable (503). See errors.

Authorizations

Authorization

string

header

required

Send Authorization: Bearer <key>. Testnet: lum_test_…; Mainnet: lum_live_…. A key works only on its own network, so pick the server that matches it (the other network answers 401). Publishable lum_pub_… keys call read-only methods only, from an allowed browser origin. Dashboard sessions and webhook keys are not accepted.

Headers

Idempotency-Key

string

Optional, and not used for deduplication: the response then carries X-Lumeus-Idempotency: ignored. To retry sendTransaction safely, resubmit the same signed envelope (the node answers DUPLICATE).

Required string length: 8 - 128

Example:

"retry-0001-2026-10-22"

Body

application/json

Runs a Soroban transaction without submitting it and returns its result, footprint, resource fee and required authorization. 5 credits plus one per started 64 KiB of response. Named params only (positional arrays are rejected). A params member set to null (as Python stellar-sdk sends for unset options) is treated as omitted at any depth.

jsonrpc

enum<string>

required

Always 2.0.

Available options:

2.0

integer

required

Request ID, echoed in the response. Send one on every call: a call without an id is a notification, which runs but gets an empty 204 response. A string ID (at most 1024 bytes) also works and is echoed unchanged.

Example:

1

method

enum<string>

required

Available options:

simulateTransaction

params

object

required

Show child attributes

Response

The simulateTransaction result. Check error before reading result.

Result
Error

A JSON-RPC 2.0 response: result on success, error otherwise. A JSON-RPC error can arrive with HTTP 200 (for example from the node, or for one child of a batch). Gateway errors carry the code string in error.data and the request ID in error.request_id; they echo your id when the body is a parseable single request and use a null id when it cannot be determined. Preserve integer IDs exactly; avoid unsafe JavaScript numeric IDs. The gateway never answers 502 or 504.

jsonrpc

enum<string>

required

Available options:

2.0

integer | null

required

The id of your call, echoed unchanged (a string id comes back as a string). null when the gateway cannot read the id, for example for invalid JSON.

result

simulateTransaction result · object

required

The simulateTransaction result, as returned by stellar-rpc 29.

Show child attributes

error

object

Show child attributes

Example:

{
  "code": -32000,
  "message": "valid API key required",
  "data": "unauthorized",
  "request_id": "req_0123456789abcdef01234567"
}

Activity API

Assets API

Webhooks

RPC

Account

simulateTransaction

Result

Parameters

Credits and limits

Errors

Authorizations

Headers

Body

Response

​Result

​Parameters

​Credits and limits

​Errors

Authorizations

Headers

Body

Response

Result

Parameters

Credits and limits

Errors