Repeated content is a maintenance trap disguised as a convenience. The day you update one copy of a fact and miss another, your documentation starts lying — and a reader who catches one lie stops trusting all of it. Single-sourcing is the discipline of writing each fact exactly once and including it everywhere it’s needed, so it can never fall out of sync with itself.
Duplication feels harmless when you create it — it’s just copy-paste. The cost arrives months later, invisibly, when the base URL changes and three of the seven pages that mention it quietly become wrong. Single-sourcing pays a small cost now to avoid a large, untraceable one later.
What to single-source
- Volatile facts — base URLs, product and version names, pricing, support addresses, rate limits. Anything that can change should live in exactly one variable.
- Shared procedures — ‘how to get an API key’ appears across a dozen guides; write it once as an includable snippet and reference it everywhere.
- Warnings and prerequisites that recur across pages, so a critical caveat is never updated in one place and forgotten in five others.
Most docs toolchains support this through variables, snippets, or includes. The mechanism matters less than the habit: when a fact changes, you change it in one place and every page that references it updates automatically.
Search your docs for your own base URL, or your product’s version number. How many times does it appear, hard-coded? Every hit is a place that will need a human to remember it on the day it changes. That count is the size of your future drift problem — and single-sourcing reduces it to one.
Decide what is canonical
Reuse is a discipline, not just a feature. For every important concept, decide which page is its canonical home, and make every other mention link to it rather than re-explain it. This does two things: it keeps a single source of truth, and it stops the same topic being documented three subtly different (and subtly contradictory) ways across your site.
‘How to authenticate’ deserves one canonical page. Your webhooks guide, your SDK guide and your rate-limits guide should each link to it, not restate it. When your auth flow changes, you edit one page and every guide is instantly correct. Restate it in each guide instead, and one day a reader follows an old copy, fails, and files a ticket that’s hard to trace back to the stale paragraph.
In the age of AI
Left unsupervised, AI multiplies duplication — it will happily re-explain the same concept on every page it touches, each time slightly differently, quietly seeding contradictions. Single-sourcing is the antidote: give the model the canonical snippet to reference, and instruct it to link rather than re-describe. Your review step should treat ‘this repeats a canonical fact’ as a defect, exactly as it would treat a duplicated function in code.
Answer, then press Check. Explanations appear after.
Choose oneSingle-sourcing means…
ReflectName three facts in your docs that should be single-sourced.
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