Well-founded

adj.thoughtful, capableprofessional

What it means

Resting on evidence or reasoning strong enough to deserve confidence.

Reach for it when affirming that a belief, concern, hope, or conclusion has a reliable basis

Her confidence was well-founded because every trial had met the same safety threshold.

playful
checks out
when verification can be reported informally
not when Checks out is casual and suggests a completed check rather than durable grounds.
everyday
reasonable
when the position falls within sensible judgment
not when A reasonable view may remain weakly supported.
everyday
sound
when reasoning is dependable without needing emphatic praise
not when Sound applies to methods and structures as well as beliefs, so it is less specific.
professional
credible
when a claim is believable enough to take seriously
not when Credible is a lower evidentiary bar than a well-founded claim.
professional
evidence-based
when explicit research or observed data support the claim
not when Evidence-based can overstate situations grounded partly in judgment or experience.
professional
justified
when the evidence makes a reaction or decision defensible
not when Justified can concern moral permission, while well-founded focuses on the basis for belief.
formal
substantiated
when documentation or proof has answered a challenge
not when Substantiated sounds forensic and is awkward for hope or confidence.
literary
rooted in fact
when the evidential basis should be vivid
not when The phrase is too absolute if values or forecasts also shape the conclusion.

well-founded concern
A well-founded concern about mold led to a full building inspection.
well-founded belief
Their well-founded belief rested on records from three independent archives.
well-founded confidence
Repeated drills gave the crew well-founded confidence in the evacuation plan.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.