SRD:Move Silently Skill

Check
Your Move Silently check is opposed by the Listen check of anyone who might hear you. You can move up to one-half your normal speed at no penalty. When moving at a speed greater than one-half but less than your full speed, you take a –5 penalty. It’s practically impossible (–20 penalty) to move silently while running or charging.

Noisy surfaces, such as bogs or undergrowth, are tough to move silently across. When you try to sneak across such a surface, you take a penalty on your Move Silently check as indicated below.

Action
None. A Move Silently check is included in your movement or other activity, so it is part of another action.

Special
The master of a cat familiar gains a +3 bonus on Move Silently checks.

A halfling has a +2 racial bonus on Move Silently checks.

If you have the Stealthy feat, you get a +2 bonus on Move Silently checks.