Page 4 of 8~112 min topic

Talk to an LLM from code

Measure whether the CLI LLM summarizer works

Page 4 turns “it ran” into executable checks for the command-line LLM summarizer.

~14 min this pageEvaluation

1Learn the idea

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Make the metric executable

Translate the claim into assertions or a tiny eval harness. The metric to protect is: contract-test pass rate, latency, retry count, output length. Always record the denominator (how many cases) beside any rate. A percentage without a denominator is marketing, not measurement.

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Run the checks

function parse(r){const t=r?.choices?.[0]?.message?.content;if(typeof t!=='string'||!t.trim()) throw new Error('invalid response');return t.trim();}
console.log(parse({choices:[{message:{content:' Ready. '}}]}));

Expected evidence: unreliable LLM API call. A passing assertion proves only the behavior it names; broader usefulness still needs the chapter’s full limits.

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Say what the metric does not prove

Be explicit: beating the baseline (offline fake transport producing a fixed summary) on this fixture does not prove behavior under missing choices array treated as empty success, or retries on 400. Label observations separately from conclusions so the next page inherits honest evidence about the CLI LLM summarizer.

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Lab notebook: denominator discipline

Compute contract-test pass rate, latency, retry count, output length with the denominator written beside the rate every time. For this chapter, the evaluation set is intentionally tiny; that is allowed only if you say so in the evidence. Compare against offline fake transport producing a fixed summary before celebrating.

Add one negative case aimed at missing choices array treated as empty success, or retries on 400. A suite with only happy cases cannot protect the CLI LLM summarizer when the characteristic failure appears in review.

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Worked judgment

If a check is expensive or flaky, shrink it until it is deterministic on system+user job object for an embeddings definition sentence. Flaky green builds teach the team to ignore gates. Record what this page does not prove so security-ops and mastery-ship inherit honest limits.

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Why this stage matters for the CLI LLM summarizer

At the evaluation stage for llm-api-hello, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about system+user job object for an embeddings definition sentence that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: offline fake transport producing a fixed summary.

For this page specifically, success looks like metrics with explicit denominators and a negative case while still centering the user decision to turn one user passage into a bounded one-sentence summary via an HTTP-shaped client. If you cannot point to a file, command, or assertion that proves that for the CLI LLM summarizer, stay on this page instead of advancing.

API: chat completions · Glossary: API key

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Chapter consolidation 1

Return to the llm api hello scenario and restate what this chapter proved on page validation.mdx. Name one metric, one ownership rule, and one regression test you will keep. Explain how this page connects to the previous page without repeating earlier paragraphs. If you cannot name a falsifier, the chapter is still a story rather than a controlled practice. Write the falsifier as an observable event with a threshold.

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Chapter consolidation 2

Return to the llm api hello scenario and restate what this chapter proved on page validation.mdx. Name one metric, one ownership rule, and one regression test you will keep. Explain how this page connects to the previous page without repeating earlier paragraphs. If you cannot name a falsifier, the chapter is still a story rather than a controlled practice. Write the falsifier as an observable event with a threshold.

Go deeper

Before you start

Why this matters

Write one independent check that would catch a fake pass for this lab. Prefer a check tied to contract-test pass rate, latency, retry count, output length over a check that only asserts “no exception.”

In the wild

See how this idea shows up as a product and a company — then come back to the lesson. Skills transfer across vendors.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. Is the metric computed with an explicit denominator?
2. Does a failing gold case actually fail the harness?
3. Did you separate observations from conclusions?
4. What remains unproved after these checks?

All responses are required.