The fear every design agency has about handing work to a developer is that it comes back approximately right. Spacing that drifted, type that was substituted, the interaction that was quietly dropped.
A design agency sells judgement. The spacing is deliberate, the type scale is deliberate, and the reason one element sits slightly off the grid is deliberate. Then it goes to a developer who treats the file as a suggestion, and it comes back with the type substituted, the rhythm gone and nobody quite able to say why it looks cheaper.
Most of that is not laziness. It is a developer meeting something genuinely difficult to implement — a layout that breaks at an awkward width, an animation that will fight the browser — and solving it silently rather than coming back to ask.
Our rule is that we raise it instead. If something in the design will cause a problem once it is real, you hear about it while there is still time to decide, and the decision stays yours. That is slower than quietly simplifying and it is the only way the thing you drew is the thing that ships.
Figma, Sketch, XD or a written brief. We work from what you have rather than asking you to redo it in our preferred tool.
The scale you set, not approximated. If a typeface cannot be licensed for web we tell you before the build rather than substituting it.
A layout that breaks at 900px, an interaction that will be painful on a phone. You hear about it while it is still cheap to change.
Designs rarely cover every width. Rather than invent the in-between states we agree them with you.
So your client can update content without the design falling apart, which is what protects your work after handover.
No credit in the footer, nothing in the code, nothing in the documentation. Your client sees your agency.
A layout that works with the ideal heading breaks with a real one. We will show you where, and suggest how to hold it.
Some effects cost ten times what they look like they should. We will tell you the price rather than absorb it or drop it silently.
Contrast below AA, or an interaction that cannot be used by keyboard. We will say so, and propose an alternative that keeps the intent.
Including the parts that will be awkward and what they would cost. We would rather have that conversation before you have quoted your client than after.