Net debt/EBITDA is the credit market's language: under 2× conservative, 3–4× stretched, above 5× fragile. Interest coverage below 2× is a warning and below 1× means operations do not cover the interest bill. Altman Z and Piotroski F are ranking tools, not theses.
Leverage magnifies equity returns when cash flows are contractual, and deleveraging is itself an equity story. On the short side what matters is not the ratio but the calendar: when maturities fall due, at what rate they will refinance, and which covenant is closest to breach. Read the debt footnote in full, then check the revolver.
Operating leases, pension deficits, contingent consideration, factored receivables, supply-chain finance and decommissioning obligations are all claims ahead of you in the queue. For any cash-burning company, compute months of runway — cash plus undrawn committed facilities over monthly burn. Under twelve months an equity raise becomes probable; under six it is near-certain, and usually at a discount.
Educational, not investment advice.