Verification Handbook for Investigative Reporting

Free, and the guide for the part of an investigation that now happens online. Edited by Craig Silverman for the European Journalism Centre, it applies verification to long-form work: search and research techniques for online investigations, checking open data before building a story on it, fact-checking and using material posted by members of the public ethically. It dates from 2015, so specific platforms and sites have moved on, but the habits it teaches, tracing where a claim or dataset really came from and documenting each step, have not. Read it for the method and update the tools yourself.