How can I query an API to get my erc20 token balance of an address in JSON format?

Question

Is there an api where I can query if an address contains an erc20 token? I need it returned in JSON format.

Answer 1

Slightly different to what you asked... (in that in the below we're querying an ERC-20 token contract to see if it contains a balance for a specific address).

The following API will allow you to query an ERC-20 token contract (at a given address) for the balance associated with a particular account address.

From https://etherscan.io/apis#tokens:

https://api.etherscan.io/api?module=account&action=tokenbalance&contractaddress=<contract_address>&address=<address_to_query>&tag=latest&apikey=YourApiKeyToken

(It works without specifying an API key, but might be rate limited.)