に過ぎない|にすぎない

1. 1Is merely or nothing more than X; limits or plays down the nature, status, or weight of something.Ex. 1
2. 2Is only X in amount or degree; emphasizes that a quantity or level is small.

Somewhat formal and stiff, it is common in writing, speeches, and serious discussion, though it is also heard in conversation. It limits or plays down something, often with 単なる, ただの, or わずか. Aimed at others it can sound dismissive, while applied to one's own view (私の意見に過ぎません) it works as a modest hedge. Unlike にほかならない, which asserts that something is precisely X, に過ぎない minimizes it.

• でしかないN2「でしかない」 is common in both speech and writing and carries a stronger subjective evaluative tone; it is often interchangeable with 「に過ぎない」 in the 'merely' sense, but it does not attach to verbs. It can also emphasize positive feelings, as in 「感謝でしかない」, where 「に過ぎない」 cannot be used.
• にほかならないN2「にほかならない」 means 'is precisely/nothing but' and is a confident affirmative assertion, not a limiting or downplaying expression, so it cannot be swapped with 「に過ぎない」. When attaching to verbs, use 「こと」, or attach 「から」 or 「ため」 to emphasize a reason or purpose.
• くらいのものだN1「くらいのものだ」 is stylistically neutral but always carries a subjective evaluation, and can also use 「〜のは〜くらいのものだ」 to mean 'only X can...'. It is interchangeable with 「に過ぎない」 only in the 'merely...' sense, not for objective limitation.

〜にすぎない is the same pattern written in hiragana, and でしかない is a close synonym with a more subjective, often more negative 'nothing but' feel. にほかならない instead asserts that something is exactly X, and くらいのものだ singles out one thing as about the only case ('about the only one is…').