This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
If A is B's agent, and as part of the contract of employment, A agrees to be personally liable to B on all contracts made by A for B with third persons, A's promise is not within this clause of the statute.1 In such cases A is known as a del credere agent. Like some of the other rules on this subject it is easier to state this than to explain it. Probably the best explanation why such a promise is not within the statute is that it is not intended by the parties as a promise to pay the debt of others, though it can be performed only by paying such debts, but, like a contract of insurance, it provides for indemnity against loss due to the acts of such agent.