Despite a global shift toward requiring Grid-Forming (GFM) capability for Power Electronics Interfaced Resources, there is still no consensus on how to verify GFM behavior during the network connection process. The response of GFM units, as implemented in the context of Power Park Modules (PPMs) including Electricity Storage Module (ESM), depends on several factors, such as the type of network disturbance (e.g., RoCoF events, voltage phase angle jumps, voltage magnitude changes), the tuning of GFM control parameters, and the physical network impedances. As a result, classical time-domain performance metrics—such as settling time, damping ratio, and rise time among others - can significantly vary depending on the specific test scenario. This variability highlights the need for refined test-specific performance requirements. One promising approach to tackle this issue is the use of envelope-based criteria to define GFM compliance criteria tailored to each test configuration. This work introduces envelope-based criteria to define GFM requirements which are aligned with the latest ENTSO-E recommendations for Power Park Modules. These envelopes are based on the expected ideal behaviour of GFM inverters and cover the minimum requirement expected from ENTSO-E, while incorporating margins around the ideal response to accommodate variations in implementation across different manufacturers. In order to validate their relevance, a generic open-source RMS model is used with different parameters and control structures. The different choices done into the implementation of the model will be detailed alongside their impact on the installation’s dynamic behavior. This model was previously compared to an equivalent EMT model to assess its representativeness and both models are used to show their ability to meet the envelope-based pass/fail criteria. The validation of the proposed envelope criteria is based on a set of various test scenarios. These tests notably include: (1) voltage phase angle jump, (2) voltage magnitude jump, (3) response to Rate of Change of Frequency (RoCoF) events, and (4) response to variation on the grid topology (Short Circuit Ratio step). The contributions of this paper are thus twofold: introducing the use of envelope-based criteria for GFM compliance criteria and validating their relevance by simulations with an open-source RMS model.