A recommendation letter may be requested either by a former employee who is currently searching for a job, or by a present employee whose departure is already planned (as in the example below).
As in the case of the employment certificate, the person’s technical and human (i.e. "behavioral") skills, as well as his/her attitude and performance will have to be assessed with great impartiality. Your personal credibility is indeed at stake, and it is recommended not to exaggerate the merits of your former employee.
Here is a sample recommendation letter based on the same case study as in the article "How to Write the Employment Certificate". You can also refer to the same evaluation form for the appraisal of the employee's performance and behavior (sample) that was proposed for the preparation of the employment certificate.