Long documents and chunking

A 200-page PDF is not one prompt. Treating it as one is the reason responses about long documents feel shallow — the model is spreading attention across too much material. This lesson teaches the mental model for breaking a long document into manageable pieces without losing the thread.

What the context window actually limits

The context window holds everything: your instructions, the document, the conversation history, and Claude's response. If the document is very large, there is less room for everything else. More importantly, research on large language models consistently shows that retrieval accuracy degrades for content buried in the middle of a very long context. The beginning and end are retrieved more reliably.

This is not a bug to work around. It is a property to design for.

The chunking mental model

Think of the document in three layers:

1. Structure — table of contents, section headings, executive summary. Read this layer first. Ask Claude to map the document's structure before you ask about any content.
2. Target section — the chapter or section that contains what you actually need. Paste or attach only this section.
3. Cross-section synthesis — if you need to connect two sections (e.g., "how does the methodology in section 2 affect the conclusions in section 5?"), paste both sections in a single message with your connecting question.

Walk-through

Take a long document — a report, a spec, a lease. Do this sequence:

1. Paste the table of contents or first two pages. Ask: "What is the structure of this document and where would I find information about [your topic]?"
2. Open the section Claude points to. Paste just that section. Ask your actual question.
3. If the answer references something in another section, paste that section too and ask Claude to reconcile the two.

At no point do you need to paste the whole document. The three-step sequence gets you a more precise answer than dumping all 200 pages.

If you get stuck

• "I don't know which section to read" — That is what step 1 is for. Paste the structure and ask Claude to orient you.
• "The sections are long too" — Break the section into thirds. Paste the first third and ask your question; then paste the second third with "continuing from the previous paste." Claude will carry the thread.
• "I need an answer that spans the whole document" — Ask Claude to generate a structured set of questions you can answer section by section, then send it the answers. You become the retrieval layer; Claude does the synthesis.

Cross-reference

If you find yourself doing this kind of multi-session work repeatedly, "Save what works as a Project" shows how to keep the document on a persistent shelf so you are not re-attaching it every session.

Deliverable

You have extracted a precise answer from a document longer than 20 pages without pasting the whole thing. The success criterion: the answer Claude gave you contains a specific detail (a number, a date, a quoted phrase) that is verifiable by opening the source document and finding that exact detail in the section you pasted.