Look up pending transactions

When transactions are submitted to the blockchain for processing, they are queued in the node memory pool to await delivery to a mining node as new work to be validated. Endpoints related to memory pool activity are peer-to-peer endpoints that enable communication between memory pools on different nodes.

With the /mempool/lookup endpoint, you can specify a list of transaction request keys to look for in the mempool portion of the peer-to-peer network. For each transaction request key, the endpoint returns the Pending tag and details about the transaction or the Missing tag.

Request format

Use POST https://{baseURL}/chain/{chain}/mempool/lookup to look up pending transactions in the memory pool.

Path parameters

Parameter	Type	Description
chain (required)	integer >= 0	Specifies the chain identifier for the chain you want to send the request to. Valid values are 0 to 19. For example, to get pending transactions for the first chain (0), the request is POST https://{baseURL}/chain/0/mempool/lookup.

Request body schema

The request body consists of an array of transaction request keys to check for in the memory pool. Each request key for a Pact transaction is a Base64Url-encoded string—without padding—that consists of 43 characters from the a-zA-Z0-9_- character set. The request body is an array of these strings.

Responses

Requests to POST https://{baseURL}/chain/{chain}/mempool/lookup return the following response code:

• 200 OK indicates that the request succeeded and the response body returns an array of lookup results for each specified transaction. The array has the same size as the request body.

Response header

The response header parameters are the same for all successful and unsuccessful Chainweb node requests.

Parameter	Type	Description
x-peer-addr	string	Specifies the host address and port number of the client as observed by the remote Chainweb node. The host address can be a domain name or an IP address in IPv4 or IPv6 format. For example: "10.36.1.3:42988".
x-server‑timestamp	integer >= 0	Specifies the clock time of the remote Chainweb node using the UNIX epoch timestamp. For example: 1618597601.
x‑chainweb‑node‑version	string	Specifies the version of the remote Chainweb node. For example: "2.23".

Successful response schema

If the request is successful, the response returns application/json content with an array of lookup results for each request key in the request body.

Parameter	Type	Description
tag	string	Specifies the lookup result. The valid return values are "Missing" or "Pending".
contents	string	Specifies the JSON-encoded text for a signed Pact transaction.

Examples

You can send a request to a bootstrap node for the Kadena test network and chain id 1 with a call like this:

POST https://us1.testnet.chainweb.com/chainweb/0.0/testnet04/chain/1/mempool/lookup

For this example, the request body consists of two request keys:

["ptI7wQeOmOt-BER2KQGVd0o6axBpqbhMPQVkkq5YAyE","Gc17hqzSZinUt-JCPvH6k_GJFXEJtRwU1Bx4OtSnxWU"]

In this example, the first transaction is "Pending" and the second transaction is "Missing" in the memory pool:

[
    {
        "tag": "Pending",
        "contents": "{\"hash\":\"ptI7wQeOmOt-BER2KQGVd0o6axBpqbhMPQVkkq5YAyE\",\"sigs\":[{\"sig\":\"1569af1b56cddd4b853b7d49249c4c52d55e59e04910bfeb8aacbd02bfa0637bbe81b0f4b48ba8eb101fa0e8a276023fbfa57fa5a835741b346d574897052201\"}],\"cmd\":\"{\\\"signers\\\":[{\\\"pubKey\\\":\\\"1d5a5e10eb15355422ad66b6c12167bdbb23b1e1ef674ea032175d220b242ed4\\\",\\\"clist\\\":[{\\\"name\\\":\\\"coin.TRANSFER\\\",\\\"args\\\":[\\\"k:1d5a5e10eb15355422ad66b6c12167bdbb23b1e1ef674ea032175d220b242ed4\\\",\\\"k:58705e8699678bd15bbda2cf40fa236694895db614aafc82cf1c06c014ca963c\\\",10]},{\\\"name\\\":\\\"coin.GAS\\\",\\\"args\\\":[]}]}],\\\"meta\\\":{\\\"creationTime\\\":1721947429,\\\"ttl\\\":32441,\\\"chainId\\\":\\\"1\\\",\\\"gasPrice\\\":1.9981e-7,\\\"gasLimit\\\":2320,\\\"sender\\\":\\\"k:1d5a5e10eb15355422ad66b6c12167bdbb23b1e1ef674ea032175d220b242ed4\\\"},\\\"nonce\\\":\\\"chainweaver\\\",\\\"networkId\\\":\\\"testnet04\\\",\\\"payload\\\":{\\\"exec\\\":{\\\"code\\\":\\\"(coin.transfer \\\\\\\"k:1d5a5e10eb15355422ad66b6c12167bdbb23b1e1ef674ea032175d220b242ed4\\\\\\\" \\\\\\\"k:58705e8699678bd15bbda2cf40fa236694895db614aafc82cf1c06c014ca963c\\\\\\\" 10.0)\\\",\\\"data\\\":null}}}\"}"
    },
    {
        "tag": "Missing"
    }
]