Sources

A comprehensive 17th-century dharmaśāstra digest (nibandha) by Vaidyanātha Dīkṣita, organized into several kāṇḍas (sections) — including a śrāddha-kāṇḍa and a varṇāśrama-dharma-kāṇḍa — covering saṃskāra, ācāra, vrata and śrāddha rules. Also cited here under its author's name, as "Vaidyanātha-dīkṣitīyam".

The official website of the Kāñcī Kāmakoṭi Pīṭha, a prominent Advaita maṭha in Kāñcīpuram. Cited mainly for the ārādhanā (commemoration) days of its succession of pontiffs.

An anthology of verses on the pontiffs (jagadgurus) of the Kāñcī Kāmakoṭi Pīṭha. Cited here via its Pariśiṣṭam (appendix) for the ārādhanā-day verse of each pontiff.

A well-known account of the sixty-three Nāyanmār (Śaiva) saints, by Swami Sivananda, published by The Divine Life Society. Cited for the gurupūjā day of each Nāyanmār.

A nibandha on vratas and their correct observance, cited here (in places via its Ānandāśrama edition) for vrata-specific timing rules.

A 17th-century dharmaśāstra digest by Anantadeva, a contemporary of Vaidyanātha Dīkṣita, covering much the same ground of saṃskāra, ācāra and vrata rules.

The largest of the eighteen mahāpurāṇas, with extensive māhātmya (glorification) material for numerous vratas, tīrthas and festivals.

A festival-information website, cited across many individual pages — a good future candidate for Wayback Machine archiving, since web pages can disappear.

One of the eighteen mahāpurāṇas, notable for its detailed pūrvabhāga treatment of monthly vratas and tithi observances.

A nibandha specifically on determining (nirṇaya) the correct day for observing a vrata when its tithi spans two sunrises.

Scholarship by the Indologist Franz Kielhorn on Hindu calendrical chronology.

A periodical carrying articles on Vedic and smārta ritual practice, cited here by monthly issue.

One of the eighteen mahāpurāṇas, with extensive vrata and tīrtha māhātmya material spread across its several khaṇḍas.

A widely-followed 17th-century nibandha by Kamalākara Bhaṭṭa on the correct determination of ritual timing — a close counterpart to Dharmasindhu.

A massive 13th-century nibandha by Hemādri, minister under the Yādavas of Devagiri, covering dāna, vrata, tīrtha and mokṣa in four separate sections — hence "catur-varga", the four goals of life.

A nibandha compiling essential ritual duties (kṛtya), cited here mainly for vrata and pūjā timing.

A purāṇa specific to Kashmir, describing the region's customs, geography and festival calendar — distinct from the pan-Indian mahāpurāṇas most other sources here draw from.

Often treated as a later continuation ("uttara") of the Bhaviṣya Purāṇa, also rich in vrata and dāna material.

One of the eighteen mahāpurāṇas, notable for extensive content on vratas, tithi observances and sun-worship.

A widely used nibandha by Kāśīnātha Upādhyāya summarizing dharmaśāstra ritual practice, especially popular in Maharashtra — a close counterpart to Nirṇayasindhu.

A smṛti text on the observance of vratas.

A text specifically on vratas — its title translates to "crest-jewel of vratas".