LLMs can look brilliant in the lab, then wobble in production. Inputs shift; edge cases pile up; cost and latency spike at the worst times. Blind spots creep in as prompts, tools, and caches stack up. Evals keep the system honest by turning quality into a repeatable, trackable practice.
This guide shows how to design evals that map to real goals, catch regressions early, and prove lift before rollout. Expect a practical loop: offline trials, online checks, and A/B tests with real users.
Quick links: Why AI evals matter • Crafting a thorough evaluation framework • Integrating evaluations into an enterprise environment • Driving continuous growth and refinement • Closing thoughts
Model outputs shift with context and load; even small prompt or tool changes can cascade. Evals pressure test that behavior and anchor decisions to a repeatable baseline tied to user goals.
Here is what good evals actually do:
Define success in concrete terms. Role, goal, and labels make quality legible, not vibes. Lenny Rachitsky’s guide on LLM-as-judge is a crisp blueprint for that setup Beyond Vibe Checks.
Expose brittleness fast. Target tricky inputs and adversarial edge cases; mix component checks with end-to-end runs. The community’s take on the four eval types is a handy map 4 types of evals.
Balance offline control with online reality. Vercel’s overview covers dataset runs and scoring patterns An introduction to evals, and Statsig’s docs show how to layer offline and online flows without guesswork Statsig docs. Chip Huyen’s product-first approach keeps the loop honest about outcomes and cost AI engineering with Chip Huyen.
Prove value before rollout. A/B tests are still the decision-maker; the LocalLLaMA note is blunt on why The Most Underrated Tool in AI Evals. Use LLM-as-judge to scale reviews, then confirm with experiments.
When frameworks feel scarce, the community has plenty of field notes. Threads on agent evals r/AI_Agents and platform options r/LLMDevs are practical reads.
Start with the end: what counts as “good”? Tie evaluation criteria to user outcomes and cost, not just model cleverness. Chip Huyen’s writeup pushes this product-first mindset, which keeps everyone aligned on impact AI engineering with Chip Huyen.
Track a focused metric set and keep signals clean:
Correctness: factual accuracy and task success
Clarity: readability, brevity, structure
Safety: toxicity and policy alignment
Blend code checks, human review, and LLM-as-judge to get coverage across reference-based and referenceless evaluations 4 types of evals.
Build your first eval in six steps:
Define roles, goals, and labels. Spell out what a “good” answer means with examples and counterexamples. Lenny’s LLM-as-judge guidance is a helpful template Beyond Vibe Checks.
Assemble a dataset from real traffic. Start small; expand to edge cases and hard negatives.
Choose scoring methods. Combine reference checks, structured rubrics, and LLM judges. Keep prompts for judges versioned and audited.
Set the pattern: dataset → runner → scorer. This makes evals repeatable and automatable; Vercel’s guide shows the basics An introduction to evals.
Run offline trials for control, then add online feedback for reality. Statsig’s docs outline an easy path for both flows Statsig docs.
Gate launches with A/B tests. Shadow candidates, protect users, then experiment when confident. The community reminder stands: experiments are the gold standard The Most Underrated Tool in AI Evals.
Small pro move: track quality, cost, and latency together. Trade-offs become obvious when these sit side by side.
As stacks grow, ad hoc notebooks turn into drift. It is time for one control surface with versioning, approvals, and clear ownership. Statsig Evals and Experiments are built for this kind of workflow, tying offline checks, online grades, and A/B tests into one place Statsig docs.
What good looks like in practice:
Single source of truth for prompts, datasets, and scorers. Assign owners; track versions; lock production picks. Vercel’s intro shows a minimal stack to start An introduction to evals.
Policy as code. Gate risky changes behind org rules, reviews, and CI checks. Chip Huyen’s approach is a good mental model AI engineering with Chip Huyen.
Layered checks for company goals: safety, quality, cost, latency. Keep signals independent so one metric cannot hide another.
A/B discipline. Measure business lift with controlled experiments; optimize toward a clear North Star. The LocalLLaMA note does not mince words on this The Most Underrated Tool in AI Evals.
A simple rollout path works well:
Run offline checks on sampled production prompts; block regressions before users see them.
Add online shadow evals on live traffic with zero user impact; validate behavior under load Statsig docs.
Launch behind a flag, then move to A/B once the candidate is stable and safe.
If a platform choice is still open, compare options with notes from the r/LLMDevs community platform discussion.
Set baselines, then keep the loop tight. Review error categories weekly; watch for drift and unscoped asks. Use LLM-as-judge where human signal is scarce, but keep prompts and rubrics stable for consistency Beyond Vibe Checks.
Work the loop: analyze → measure → improve. Run offline evals on fixed sets for regression checks; run online grades on live outputs to catch real-world failure modes. Vercel’s intro and the Statsig overview show both sides of that loop in practice An introduction to evals Statsig docs.
Roll out in phases: canary traffic first; add shadow prompts; then ship to an experiment. Confirm wins with A/B tests; real users decide value, not judges. Chip Huyen’s playbook and the LocalLLaMA thread both underline this point AI engineering with Chip Huyen The Most Underrated Tool in AI Evals.
Prune noise and isolate failure modes. Use component checks for tools, end-to-end black-box checks for outcomes, and mix reference-based with referenceless scoring for coverage 4 types of evals.
Practical moves that age well:
Audit a small random sample daily; tag root causes.
Rotate prompts behind flags; catch silent regressions early.
Gate launches; scale only after metric wins are clear.
Log eval scores alongside latency and cost; plot trends to spot drift.
For more field notes and teams’ methods, see Pragmatic Engineer’s roundups AI engineering in the real world, the r/AIQuality deep dive on evals field notes, and the agent-specific hurdles thread r/AI_Agents.
Evals do the unglamorous work: define success, catch regressions, and prove lift. Use offline trials for control, online checks for reality, and experiments for truth. Keep the loop tight and the goals clear.
Want to dig deeper?
Lenny Rachitsky on LLM-as-judge and practical rubrics Beyond Vibe Checks
Vercel’s overview of datasets, runners, and scoring An introduction to evals
Chip Huyen on product-first AI engineering AI engineering with Chip Huyen
Statsig’s docs on offline and online evals, plus experiments Statsig docs
Community threads on platforms and agent-specific evals platform options agent evals
Hope you find this useful!