Vedas are considered the foundational, impersonal (apauruseya) divine revelations focusing on cosmic order, philosophy, and Yagnas (rituals), while Agamas are later, sectarian theological treatises detailing practical deity worship, temple construction, and rituals (tantras/mantras). Vedas are universal, whereas Agamas (Shaiva, Vaishnava, Shakta) are specific to denominations, often acting as applied, accessible spiritual technology.
Key Differences Between Agamas and Vedas:
Origin & Nature: Vedas are considered eternal and apauruseya (not of human origin). Agamas are generally considered to be revealed by God (e.g., Shiva to Parvati, Vishnu to Lakshmi) but are often treated as more specific to particular traditions.

Scope & Focus: Vedas (Nigamas) primarily focus on philosophical knowledge, hymns, and ritual sacrifices (Yajnas). Agamas focus on practical applications: temple architecture, idol installation, and daily worship rituals (Kriya/Charya).
Time Period: The Vedas are the oldest, dating back to the 1st millennium BCE or earlier. The Agamas are later, generally originating in the early centuries of the common era.

Authority & Structure: While Vedas are the ultimate authority, Agamas are regarded as authoritative within specific sects (Shaiva, Vaishnava, Shakta) and are often seen as "milk" to the "cow" of the Vedas.
Accessibility: Vedic rituals often required specific Vedic qualifications. The Agamas were formulated to be more accessible, often opening worship, mantra, and initiation to all castes and both genders.
Relationship:

Complementary: Many traditions view them as complementary: Vedas provide the knowledge, and Agamas provide the practical, applied technology.
Derivative: In many contexts, Agamas are considered to have evolved from the Vedic, Upanishadic, and Puranic traditions to suit a more personal form of deity worship.
Examples:
Vedas: Rig, Yajur, Sama, Atharva.
Agamas: Kamika Agama (Shaiva), Pancharatra Agama (Vaishnava).

I feel it is Timeless