# Define once, cite everywhere > Source: > Published: 2026-08-21 08:55:24+00:00 Run this on any repo doing spec-driven development: ``` grep -rn -i "refund" openspec/specs ``` Mine returned: ``` billing/spec.md:4: Refunds are issued for purchases made in the last 30 days. checkout/spec.md:4: Customers can request a refund within 30 days of delivery. support/spec.md:4: If the order is less than a month old, offer a refund. ``` Same rule, three specs, three wordings — and two meanings. 30 days from **purchase** is not 30 days from **delivery**. Nobody decided that fork. A coding agent paraphrased it into existence, and no human caught it, because nobody reads specs anymore — only agents do. As truth. We fixed this in code decades ago: don't repeat yourself. Specs never got the memo. **The fix: define the rule once, and let every spec cite it** — one line, carrying a content digest: ``` Refunds follow BR-REFUND-001. {pdac:cite id="BR-REFUND-001" digest="sha256:b5c5…"} ``` When the rule changes through your normal review flow, one command flags every citing spec — file and line, no grep: ``` bash $ prodshape citations verify stale BR-REFUND-001 openspec/specs/billing/spec.md:4 stale BR-REFUND-001 openspec/specs/checkout/spec.md:4 stale BR-REFUND-001 openspec/specs/support/spec.md:4 ``` Put it in CI and stale product knowledge stops being invisible. Specs get shorter, forks become impossible, drift becomes detectable. Full 30-second demo (real output, `@prodshape/cli@0.12.0` , no setup): .[https://jgcarmona.com/en/define-once-cite-everywhere/](https://jgcarmona.com/en/define-once-cite-everywhere/). The idea behind it: [Product Definition as Code](https://pdac.dev) — one versioned product model that specs and agents cite instead of re-derive, upstream of whatever SDD tool you use. **Try the grep on your own specs and count your forks.** Found one? Tell me in the comments — I'll help you set this up in 15 minutes.