A written agreement does not determine worker classification, but a badly drafted one supplies evidence against it.
Terms that support contractor status. Definition of the deliverable rather than of hours; the contractor’s control over how and when the work is done; the contractor’s provision of its own tools and workspace; the right to engage assistants; freedom to work for others; payment by project or invoice rather than by salaried period; and the contractor’s responsibility for its own taxes, insurance and licences.
Terms that undermine it. Fixed schedules and reporting hours; a requirement to attend regular internal meetings; company email addresses and inclusion in the directory; performance reviews; company-provided equipment; an exclusivity provision; a notice period resembling employment; and language describing termination for cause using employment concepts.
Necessary protections that do not undermine it. Confidentiality, assignment of work product with a present-tense assignment, indemnity, insurance requirements, and compliance obligations.
Term and termination. Project-based with a completion event, or a term with termination for convenience on notice.
Substitution. The right to subcontract, subject to consent not unreasonably withheld, is strong evidence of contractor status.
Practice matters more. An agreement describing an independent relationship, administered as employment, is evidence of a misclassification that was understood.