Page 2 of 8~112 min topic

Talk to an LLM from code

Define the CLI LLM summarizer input contract

Page 2 hardens the boundary around the command-line LLM summarizer so bad inputs fail before the interesting algorithm runs.

~14 min this pageData contract

1Learn the idea

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Define what may enter

The accepted input remains: non-empty text, model name, timeout, API key from environment. Keep parsing and normalization in functions that do not score, train, or call a model. That split lets a test fail the boundary without blaming the core logic. The user-facing decision stays: turn one user passage into a bounded one-sentence summary via an HTTP-shaped client.

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Reject at the boundary

function request(text){if(!text.trim()) throw new Error('text required'); return {model:'demo',messages:[{role:'system',content:'One sentence.'},{role:'user',content:text}],max_tokens:60};}
console.log(request('Vectors support retrieval.'));

Expected evidence: a request object with model, two roles, and max_tokens. If the contract is silent on a bad value, later debugging will look like an algorithm bug when it is really a data bug.

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Keep transforms testable

Write one assertion for a neighboring valid input to the CLI LLM summarizer so tightening the boundary does not over-reject. Document field names and types the way a teammate would need them on day two of llm-api-hello—not as comments you plan to delete.

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Lab notebook: name the fields

List every field in system+user job object for an embeddings definition sentence and mark each as required, optional, or forbidden. Required fields must fail loudly when missing; optional fields need defaults you can quote in a test; forbidden fields (secrets, raw PII, path escapes) must never be accepted silently. This list is the contract for the CLI LLM summarizer.

Add one sentence about encoding, units, or timezones if relevant to non-empty text, model name, timeout, API key from environment. Contracts that ignore units create “correct” programs that still ship wrong decisions when someone tries to turn one user passage into a bounded one-sentence summary via an HTTP-shaped client.

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Worked judgment

Write the error string you want for the most likely bad input. Prefer ValueError('threshold out of range')-style messages over generic invalid input. The contract’s job is to make missing choices array treated as empty success, or retries on 400 harder to confuse with a model or algorithm bug later.

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Why this stage matters for the CLI LLM summarizer

At the data contract 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 malformed inputs rejected with field-named errors 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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Before you start

Why this matters

Invent one malformed input that the command-line LLM summarizer might accidentally accept. Predict the exception or rejection message. After you run the contract code, compare your prediction with the real failure text.

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.

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Page assessment

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

1. Which malformed values die before core logic?
2. Can transform and prediction/search be tested separately?
3. Does the error name the violated field or shape?
4. Is the accepted input still exactly: non-empty text, model name, timeout, API key from environment?

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