It measures 13 to 16 cm and weighs 9 to 17 g. Both sexes similar. It has yellowish to light brown irises, yellowish to greenish legs, and black to gray bill. Nominal breed has pale brownish-gray face with faint eye line, olive-grayish-brown forehead, rufous crown sometimes mottled, dull olive-brown upperparts, rufous wing-coverts, fawn brownish remiges, and long olive-brown tail with slightly outer rectrices. more rufescent. It has a whitish throat with black spots on the underside, a pale buffy gray breast, brown flanks and undercovers, and a pale belly. The young individual lacks a contrasting crown, a less defined throat patch, and paler and occasionally slightly more rufescent upperparts.
The white-breasted pijuí is found in Argentina, Bolivia, Brazil, Colombia, Costa Rica, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, Uruguay, Guatemala, and Venezuela.
It is a sedentary bird that lives in a wide spectrum of herbaceous and shrub habitats. It prefers the savannas with scattered trees and in the stubble and tall grasslands, up to 1,200 m of altitude.
In Colombia it is found below 2,100 m above sea level from the Gulf of Urabá eastward along the Caribbean Coast to Guajira, southward through the valleys of the Cauca and Magdalena rivers, on the western slope of the Eastern mountain range from the department of Norte de Santander towards the south to the west of Putumayo and towards the east through Meta, Casanare, Arauca and Vichada. Also in southern Amazonas.
The white-breasted pijuí is an insectivore difficult to see, because it searches for food among the low and dense vegetation, although it can be located by its repetitive calls that sound like güitio, from which it owes its common name in some places.
They build spherical nests with sticks with a tubular entrance about 30 cm long that they place among the low bushes. They make layings that usually consist of two greenish-white eggs.
The Azara’s Spinetail (Synallaxis azarae) has a longer and rufous tail, Silvery-throated Spinetail (Synallaxis subpudica) is larger, with a longer tail and a blackish throat. Dark-breasted Spinetail (Synallaxis albigularis) has a shorter tail and a totally white throat. The Brown Rastrojero (Synallaxis gujanensis) has a rufous tail and a grayish-brown crown.
Ten subspecies are recognized, of which seven are found in Colombia. The latitabunda race in the Gulf of Urabá, the littoralis race on the Caribbean coast, the insignis race in the Cauca and Magdalena valleys and the department of Boyacá. Also the perpallida race in the Guajira peninsula, the occipitalis race in the departments of Santander and Norte de Santander, the nesiotis subspecies in the Santa Marta region and the inaequalis race in southern Amazonas. The latitabunda subspecies is darker than the nominal race, with a more brown tail and flanks. The perpallid subspecies is similar to the previous one but less rufescent above and more grayish, with the crown and wing coverts dark rufous. The occipitalis race is darker with a blackish forehead, not grayish. The insignis subspecies is similar to the latter but paler, with a less extensive rufous crown, a paler back with a brownish tinge, a paler and less grayish chest. The littoralis subspecies differs from the previous one by more brownish upper parts and less grayish lower parts. The nesiotis race has a more yellowish tint to the crown and male than the nominal race. Its upper parts are paler and greyish and whiter underneath.
Genetic studies indicate that it forms a group with S. frontalis, S. azarae and S. courseni. The taxonomic limits of some of their races are not clear and it is probable that some populations merit recognition as distinct races.
In Colombia, individuals in reproductive condition have been registered from January to November in the north of the country and two males in reproductive condition in January in Huila. Also a nest in January in Cali and another under construction in April in the Patía Valley. Apparently it is a monogamous bird. Its nest is a globular mass 15 to 20 cm high and 18 to 30 cm long, which it builds with dry grasses, twigs (sometimes quite long and with thorns), snake skins and spider webs. It has one or two lateral inlets 15 to 40 cm long that connect to an internal chamber 10 cm in diameter covered with plant material. Its nest is built at heights ranging from 0.2 to 9 m in height on a cluster of grasses or a bush covered with lianas. It lays two to four grayish eggs, which both members of the pair incubate for 15 to 18 days. Young remain in nest for approximately 16 days. Their nests are frequently parasitized by Tapera naevia.
Their diet is mainly made up of arthropods, among which have been recorded: crickets, beetles, stick insects, bed bugs, cicadas, ants, caterpillars and spiders. On one occasion a small snail was also recorded.
At the national and international level, it is classified as a species of least concern.