All 10 tools return internal error (-32603) instead of isError for missing API token

[blackwell-systems]

When BANKLESS_API_TOKEN is not set, all 10 tools return a JSON-RPC internal error (-32603) instead of a proper tool error (isError: true). This means agents receive a protocol-level crash instead of a recoverable error message.

FAIL read_contract    internal error: Authentication Failed: BANKLESS_API_TOKEN environment variable is not set
FAIL get_proxy        internal error: Authentication Failed: BANKLESS_API_TOKEN environment variable is not set
... (all 10 tools)

Why it matters: MCP distinguishes between:

• isError: true: the tool ran but something went wrong. The error message is user-facing and the agent can recover (e.g. prompt the user for the token).
• -32603: something broke inside the server. The agent treats this as a fatal error and can't help the user.

The error message itself is excellent ("Authentication Failed: BANKLESS_API_TOKEN environment variable is not set"). It just needs to be returned as a tool error instead of an internal error.

Suggested fix:

Instead of throwing/rejecting, return the error through the MCP tool result:

if (!process.env.BANKLESS_API_TOKEN) {
  return { content: [{ type: "text", text: "Authentication Failed: BANKLESS_API_TOKEN environment variable is not set" }], isError: true };
}

Additionally: the network parameter appears in 7 tools but has no enum listing valid values. Agents must guess whether it's "ethereum", "eth", "1", or "mainnet". Adding enum: ["ethereum", "polygon", "arbitrum", ...] to the schema would reduce agent errors.

Found via: mcp-assert audit --server "npx -y @bankless/onchain-mcp" and mcp-assert lint. If you want to add CI regression testing for your server: github.com/blackwell-systems/mcp-assert.