MANTA-Ray (Modified Absorption of Non-spherical Tiny Aggregates in the RAYleigh regime) calculates the absorption efficiency and absorption cross-section of fractal aggregates. This fast tool can be used to estimate the amount of absorption that occurs in dust and haze particles of any shape, provided that the electromagnetic radiation is in the Rayleigh regime, often in the context of planetary atmospheres or protoplanetary disks. MANTA-Ray obtains values within 10-20% of those calculated by a rigorous benchmark model (the discrete dipole approximation), but is 10¹³ times faster.