contract_get_function_args
Parse a contract's ABI or use nearblocks.io API to retrieve function call arguments for NEAR blockchain. Checks recent method executions to identify likely inputs. Experimental tool.
Instructions
Get the arguments of a function call by parsing the contract's ABI or by using the nearblocks.io API (as a fallback). This function API checks recent execution results of the contract's method being queried to determine the likely arguments of the function call. Warning: This tool is experimental and is not garunteed to get the correct arguments.
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| contractId | Yes | ||
| methodName | Yes | ||
| networkId | No | mainnet |
Implementation Reference
- src/services.ts:1843-1993 (registration)Registration of the 'contract_get_function_args' MCP tool, including name, description, input schema, and handler function.
mcp.tool( 'contract_get_function_args', noLeadingWhitespace` Get the arguments of a function call by parsing the contract's ABI or by using the nearblocks.io API (as a fallback). This function API checks recent execution results of the contract's method being queried to determine the likely arguments of the function call. Warning: This tool is experimental and is not garunteed to get the correct arguments.`, { contractId: z.string(), methodName: z.string(), networkId: z.enum(['testnet', 'mainnet']).default('mainnet'), }, async (args, _) => { const connection = await connect({ networkId: args.networkId, nodeUrl: getEndpointsByNetwork(args.networkId)[0]!, }); const contractAccountResult: Result<Account, Error> = await getAccount( args.contractId, connection, ); if (!contractAccountResult.ok) { return { content: [ { type: 'text', text: `Error: ${contractAccountResult.error}` }, ], }; } const contractMethods = await getContractMethods( args.contractId, connection, ); if (!contractMethods.ok) { return { content: [ { type: 'text', text: `Error: ${contractMethods.error}`, }, ], }; } if (contractMethods.value.length === 0) { return { content: [ { type: 'text', text: `No methods found for contract ${args.contractId}`, }, ], }; } if (!contractMethods.value.includes(args.methodName)) { return { content: [ { type: 'text', text: `Method ${args.methodName} not found for contract ${args.contractId}`, }, ], }; } const parsedContractABIResult = await getContractABI( contractAccountResult.value, args.contractId, ); // if the contract ABI is not found, ignore, only return if // the contract ABI is found if (parsedContractABIResult.ok) { const abi = parsedContractABIResult.value; const method = abi.body.functions.find( (method) => method.name === args.methodName, ); if (!method) { return { content: [ { type: 'text', text: `Method ${args.methodName} not found in contract ${args.contractId}`, }, ], }; } return { content: [ { type: 'text', text: stringify_bigint({ ...method, args: method.params?.args || {}, }), }, ], }; } // TODO: This function uses near blocks api which is rate limited // and will fail if we call it too many times. We should // use another method to get the contract methods. const parsedContractMethodsResult: Result<JsonSchema7Type, Error> = await (async () => { try { const parsedMethod = await getParsedContractMethod( args.contractId, args.methodName, ); if (!parsedMethod.ok) { return parsedMethod; } const zodArgsResult = json_to_zod( parsedMethod.value.action.length > 0 ? parsedMethod.value.action[0]?.args.args_json : {}, ); if (!zodArgsResult.ok) { return zodArgsResult; } const jsonSchema = zodToJsonSchema(zodArgsResult.value); return { ok: true, value: jsonSchema, }; } catch (e) { return { ok: false, error: new Error(e as string) }; } })(); if (!parsedContractMethodsResult.ok) { return { content: [ { type: 'text', text: `Error Parsing Contract Methods: ${parsedContractMethodsResult.error}`, }, ], }; } const parsedContractMethods = parsedContractMethodsResult.value; return { content: [ { type: 'text', text: stringify_bigint(parsedContractMethods), }, ], }; }, ); - src/services.ts:1855-1992 (handler)The main handler function for the tool. Connects to NEAR, validates contract account and method existence, attempts to fetch ABI via __contract_abi for params, falls back to parsing recent tx args from nearblocks.io API using getParsedContractMethod and json_to_zod.
async (args, _) => { const connection = await connect({ networkId: args.networkId, nodeUrl: getEndpointsByNetwork(args.networkId)[0]!, }); const contractAccountResult: Result<Account, Error> = await getAccount( args.contractId, connection, ); if (!contractAccountResult.ok) { return { content: [ { type: 'text', text: `Error: ${contractAccountResult.error}` }, ], }; } const contractMethods = await getContractMethods( args.contractId, connection, ); if (!contractMethods.ok) { return { content: [ { type: 'text', text: `Error: ${contractMethods.error}`, }, ], }; } if (contractMethods.value.length === 0) { return { content: [ { type: 'text', text: `No methods found for contract ${args.contractId}`, }, ], }; } if (!contractMethods.value.includes(args.methodName)) { return { content: [ { type: 'text', text: `Method ${args.methodName} not found for contract ${args.contractId}`, }, ], }; } const parsedContractABIResult = await getContractABI( contractAccountResult.value, args.contractId, ); // if the contract ABI is not found, ignore, only return if // the contract ABI is found if (parsedContractABIResult.ok) { const abi = parsedContractABIResult.value; const method = abi.body.functions.find( (method) => method.name === args.methodName, ); if (!method) { return { content: [ { type: 'text', text: `Method ${args.methodName} not found in contract ${args.contractId}`, }, ], }; } return { content: [ { type: 'text', text: stringify_bigint({ ...method, args: method.params?.args || {}, }), }, ], }; } // TODO: This function uses near blocks api which is rate limited // and will fail if we call it too many times. We should // use another method to get the contract methods. const parsedContractMethodsResult: Result<JsonSchema7Type, Error> = await (async () => { try { const parsedMethod = await getParsedContractMethod( args.contractId, args.methodName, ); if (!parsedMethod.ok) { return parsedMethod; } const zodArgsResult = json_to_zod( parsedMethod.value.action.length > 0 ? parsedMethod.value.action[0]?.args.args_json : {}, ); if (!zodArgsResult.ok) { return zodArgsResult; } const jsonSchema = zodToJsonSchema(zodArgsResult.value); return { ok: true, value: jsonSchema, }; } catch (e) { return { ok: false, error: new Error(e as string) }; } })(); if (!parsedContractMethodsResult.ok) { return { content: [ { type: 'text', text: `Error Parsing Contract Methods: ${parsedContractMethodsResult.error}`, }, ], }; } const parsedContractMethods = parsedContractMethodsResult.value; return { content: [ { type: 'text', text: stringify_bigint(parsedContractMethods), }, ], }; }, - src/services.ts:1851-1854 (schema)Zod input schema defining parameters: contractId (string), methodName (string), networkId (testnet/mainnet, default mainnet).
contractId: z.string(), methodName: z.string(), networkId: z.enum(['testnet', 'mainnet']).default('mainnet'), }, - src/services.ts:208-232 (helper)Helper function to retrieve and parse the contract's ABI from the __contract_abi view method, used as primary source for function arguments.
const getContractABI = async ( account: Account, contractAccountId: string, ): Promise<Result<AbiRoot, Error>> => { try { const contractABICompressed: unknown = await account.viewFunction({ contractId: contractAccountId, methodName: '__contract_abi', args: {}, parse: (value) => value, }); const decoder = new ZSTDDecoder(); await decoder.init(); const contractABI = new TextDecoder().decode( decoder.decode(contractABICompressed as Buffer), ); return { ok: true, value: JSON.parse(contractABI) as AbiRoot, }; } catch (e) { return { ok: false, error: new Error(e as string) }; } }; - src/utils.ts:396-428 (helper)Fallback helper: Queries nearblocks.io API for recent executions of the method to infer argument structure from args_json.
export const getParsedContractMethod = async ( contractId: string, methodName: string, ): Promise<Result<ParsedMethod, Error>> => { try { const url = `https://api.nearblocks.io/v1/account/${contractId}/contract/${methodName}`; const response = await fetch(url); const responseJson = (await response.json()) as unknown; const parsedMethod = ParsedMethodSchema.safeParse(responseJson); if (!parsedMethod.success) { return { ok: false, error: new Error( `Error parsing args for contract ${contractId}, method ${methodName}. Got: ${JSON.stringify( responseJson, null, 2, )}`, ), }; } return { ok: true, value: parsedMethod.data, }; } catch (error) { return { ok: false, error: new Error( `Error parsing contract method ${methodName} for contract ${contractId}: ${String(error)}`, ), }; }