The evidence that reinforces itself
The strongest tenant cases usually combine several types of evidence that, together, tell a clear and credible story. No single item has to carry everything.
The most valuable kinds of evidence often include photos and videos of the conditions; written repair requests and the landlord's responses, which prove notice and timing; reports from a code or health inspector documenting violations; witness accounts from people who saw the conditions; medical records when health was affected; and receipts or proof of value for any losses. A clear, dated timeline ties it all together.
What makes evidence powerful is that the pieces reinforce each other. A photo of mold is good; a photo plus a written report to the landlord plus an inspector's finding plus medical records showing related symptoms is far stronger.
You do not need every type in every case — the right mix depends on your situation. If you want help understanding which kinds of evidence matter most for your specific problem, a free, confidential review can walk you through what to focus on gathering.
This is general information about California tenant rights, not legal advice. Every situation is different.