Ground Truth
The measurement that arbitrates, as opposed to the artifact that merely reports.
Ground truth is the observation that settles a question, as distinct from the many artifacts that describe it. Most debugging confusion comes from treating a report as a measurement.
Examples of the distinction are everywhere. A build tool's summary table is a report; the actual script tags in the served HTML are ground truth. A hosting platform's "mergeable" flag is a report; performing the merge locally is ground truth. A green exit code is a report; the count of tests that actually ran is ground truth — a filter that matched nothing exits zero. A comment claiming an invariant is a report; the type system is ground truth.
The habit worth building is to ask, for any claim you are about to act on, what would I have to look at to be wrong about this? — then look at that. It is usually cheaper than the reasoning it replaces.
Ground truth also has a staleness dimension. A measurement is only about the thing you measured, at the moment you measured it. Verifying against a server compiled before your change, or a cached artifact from a prior state, produces a real number about the wrong world. Restart, rebuild, refetch before every claim you intend to stand behind.
See also8
Hand-picked in the note itself — the neighbours worth reading next.
Falsifiability
A claim is only worth something if you know what observation would refute it.
Method16 connections
Observability
How much of a system's internal state can be inferred from what it emits.
Method15 connections
Reproducible Case
The smallest set of steps that reliably produces a fault, and the unit of real debugging.
Method17 connections
Determinism
The property that identical inputs produce identical outputs, and the foundation of caching and verification.
Systems & Tooling27 connections
Instrumentation
Adding measurement to code so its execution can be observed, and the distortions that introduces.
Testing & Verification12 connections
Silent Failure
A failure that produces no signal, so the absence of an error reads as success.
Method44 connections
Root Cause Analysis
Escalating past the visible symptom until you find the layer that actually produced it.
Method21 connections
Vacuous Truth
A statement that holds only because its subject set is empty — a green result that measured nothing.
Method25 connections
Related2
Nearby in the graph rather than deliberately chosen. Looser, sometimes surprising.
Linked from29
Notes elsewhere in the wiki that reach for this one.
- Adversarial ReviewAgents & Language Models
Reviewing work with an explicit mandate to refute it, from a perspective that did not produce it.
- BundlerWeb Platform
The tool that resolves an application's modules into the files a browser downloads.
- Character EncodingSystems & Tooling
The mapping between characters and bytes, and the source of a specific family of invisible bugs.
- Code SigningSystems & Tooling
Cryptographically attesting who produced a binary, and the operating-system checks built on it.
- Code SplittingWeb Platform
Dividing an application bundle so a page downloads only the code it needs.
- ContainerizationSystems & Tooling
Packaging an application with its dependencies into an isolated, reproducible runtime unit.
- Continuous DeploymentVersion Control & Delivery
Automatically releasing every change that passes validation.
- DaemonSystems & Tooling
A long-running background process managed by the operating system's service supervisor.
- Exhaustive ClaimMethod
A statement of the form "the last one" or "nothing else does this" — load-bearing, and only as good as the search behind it.
- FalsifiabilityMethod
A claim is only worth something if you know what observation would refute it.
- Fan-Out and Fan-InAgents & Language Models
Splitting work across parallel workers and recombining their results.
- Flaky TestTesting & Verification
A test that passes and fails on identical input, and the most corrosive thing a suite can contain.
- GlobSystems & Tooling
Wildcard pattern matching over filenames, similar enough to regular expressions to mislead.
- HallucinationAgents & Language Models
Fluent, confident output that is not grounded in anything real.
- InstrumentationTesting & Verification
Adding measurement to code so its execution can be observed, and the distortions that introduces.
- Merge ConflictVersion Control & Delivery
Overlapping changes that a merge cannot combine automatically, requiring a decision.
- Module GraphWeb Platform
The directed graph of imports that decides what code ends up where.
- ObservabilityMethod
How much of a system's internal state can be inferred from what it emits.
- Plausible MechanismMethod
A causal explanation that was inferred rather than tested, and reads as more rigorous for being specific.
- Race ConditionTesting & Verification
A defect whose occurrence depends on the relative timing of concurrent operations.
- Reproducible CaseMethod
The smallest set of steps that reliably produces a fault, and the unit of real debugging.
- Root Cause AnalysisMethod
Escalating past the visible symptom until you find the layer that actually produced it.
- Secret ManagementSystems & Tooling
Storing, distributing, and rotating credentials without embedding them in code or history.
- ShellSystems & Tooling
The interactive command interpreter, and a programming language with unusually sharp edges.
- Silent FailureMethod
A failure that produces no signal, so the absence of an error reads as success.
- SubagentAgents & Language Models
A model instance spawned by another to handle a scoped task with its own context.
- Truncation BiasMethod
Reading a truncated result as if it were the whole result, so every counterexample is invisible.
- Vacuous TruthMethod
A statement that holds only because its subject set is empty — a green result that measured nothing.
- Web Font LoadingWeb Platform
How custom typefaces are fetched and shown, and why the cost is easy to misattribute.