If the airline damaged your checked bag (cracked shell, broken wheels/handle, torn fabric, damaged contents), the Montreal Convention makes it liable up to about 1,519 SDR per passenger — but the written-complaint deadline is a strict 7 days.

[Your name / address / email / phone]
[Date]
[Airline] — Baggage Claims

Re: Damaged baggage claim — Montreal Convention 1999, Article 17(2)
    Flight [number] — [origin] to [destination] — [date]
    PIR / file reference: [____]   ·   Booking: [PNR]
    Bag tag number(s): [____]

Dear Sir or Madam,

My checked bag arrived damaged on flight [number] on [date]. The damage is
[describe: cracked shell / broken wheel / torn / damaged contents]. I
reported it [at the airport on arrival, PIR [____] / within 7 days of
receipt as required].

Under Article 17(2) of the Montreal Convention, the carrier is liable for
damage to checked baggage. I claim [the cost of repair, $/€[____] (quote
enclosed) / replacement value of $/€[____], the bag being [age] old and
beyond economic repair], plus $/€[____] for damaged contents (receipts/
photos enclosed). Total: [currency + amount], within the per-passenger
limit (currently 1,519 SDR, effective 28 December 2024).

Please settle within 14 days.

Yours faithfully,
[Signature / printed name]

You have only 7 days for damage. Article 31 requires a written complaint for damaged baggage within 7 days of receiving the bag (vs 21 days for delay). Report it at the airport baggage desk before you leave if at all possible and get the PIR — then follow up in writing immediately. After 7 days the claim is usually barred (lawsuits: 2-year limit).

Notes

Photograph the damage before any repair, and keep the bag.
Normal wear and minor marks (scuffs, scratches) are often excluded; airlines also commonly exclude fragile/perishable items and protruding parts. Focus on functional damage.
Repair vs replacement: ask for repair if economical; if the bag is destroyed or old, claim a fair (possibly depreciated) replacement value.
US domestic flight? Montreal doesn’t apply — see US passenger rights (domestic liability up to $4,700).

Damaged baggage claim letter (Montreal Convention)