How do I weigh an employer retirement match against a tight monthly budget?

The benefits slide said my US employer's retirement plan matches employee contributions dollar for dollar up to 3% of eligible pay. A colleague leaned over and said, "You'd be mad to leave free money there."

I usually have about $90 uncommitted after the monthly expenses and savings I've planned. I was considering a $50 monthly contribution, but I haven't asked payroll what that would do to my actual take-home pay. I also haven't read the plan's eligibility and vesting terms. I don't want to treat the slide as the complete agreement.

The match is appealing. The phrase 'free money' makes the decision sound finished before I've checked how the smaller current budget would work. Before deciding, I want to understand the contribution and the benefit attached to it.

What would you clarify first so you could compare the long-term opportunity with this month's breathing room? I'd like a decision based on the plan and the budget, rather than embarrassment at not immediately agreeing with my colleague.