Tolerance creep

Widening the allowed difference between two reads until they stop disagreeing. The tolerance exists to absorb rounding, not the error you just found. A count gets no tolerance at all: a default of one silently absorbs exactly the dropped or duplicated row the check was built to catch.

Principle 2 · Two independent reads beat one careful one

Where does Tolerance creep come from?

Principle 2 of the Kymira doctrine, Two independent reads beat one careful one. Tolerance creep is the name the doctrine gives to what that principle requires in practice.

What failure is Tolerance creep named after?

The tolerance that ate the error. Two reads disagreed, so the tolerance grew until they did not.

What does it look like on a real file?

A count check carrying a default tolerance of 1.0 passes a file that lost exactly one row.

Not for

Not for counts. A count matches or it does not, and no tolerance at all is the correct setting.

Nearest terms

Dual railComputing a published value twice by two routes that share as little logic as possible: once...Reconciliation anchorA total the source file states about itself, a printed grand total, a totals row, a stated...Circular checkA check whose verdict is derived from the thing it is meant to test: a total computed from the...

Last updated 2026-09-02 · Dylan, founder · one of 40 terms in the Kymira glossary, each one named after something we watched go wrong in a real build or in our own audits.

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