The purpose of a farm system is to produce talent for its parent club, whether it be directly with young players or indirectly with trades. Since becoming general manager of the Mariners in September 2015, Jerry Dipoto has pulled off 65 deals, many of which exchanged prospects or young big leaguers for veterans.
The whirlwind of trade activity did have tangible results, as Seattle went from winning 76 games in its last season before Dipoto to an average of 84 victories in three years with him at the helm. The Mariners' 89 wins in 2018 were their most since 2003, though their playoff drought extends to 2001.
While the big league club measurably improved under Dipoto, the system headed in the other direction. It was thin when he arrived, and shipping out nearly five-dozen prospects -- including Enyel de los Santos, Luiz Gohara, Nick Neidert, Tyler O'Neill, Freddy Peralta and Ryan Yarbrough -- made it even slimmer. At the outset of 2018, the consensus was that Seattle had the worst collection of prospect talent in the game.
But as 2018 draws to a close, the Mariners' system has improved more than any other in the past year and is trending up for the first time in years. The franchise reversed course this offseason, deciding that the oldest team in baseball had overachieved in 2018 (it had the run differential of a typical 77-win club) and needed a makeover. So Dipoto switched his focus in trades and started swapping veterans for prospects.
Seattle ended the regular season without a single player on MLB Pipeline's Top 100 Prospects list but now has three. Left-hander Justus Sheffield (No. 31) headlined a three-prospect package from the Yankees for James Paxton in November. Two weeks later, Robinson Cano and Edwin Diaz headed to the Mets in exchange for outfielder Jarred Kelenic (No. 62 and the sixth overall pick in the 2018 Draft), righty Justin Dunn (No. 89), two veterans and a relief prospect.

Sheffield, Kelenic and Dunn highlight a contingent of 13 prospects on our Mariners Top 30 who have joined the organization since June. Right-hander Logan Gilbert (first round), outfielder Josh Stowers (second), catcher Cal Raleigh (third) and righty Joey Gerber (eighth) arrived via the Draft. Shortstop Noelvi Marte signed for $1.55 million out of the Dominican Republic.
Dipoto made his first big offseason splash in early November, when he sent Mike Zunino to the Rays in a five-player trade that included outfielder Jake Fraley heading to Seattle. The other pieces of the deals with Paxton (right-hander Erik Swanson, outfielder Dom Thompson-Williams) and Cano/Diaz (righty Gerson Bautista) also cracked the Top 30. So did lefty Ricardo Sanchez, purchased from the Braves in November.
After all of those additions, the Mariners no longer have the least impressive prospect talent in baseball -- though they still have more work to do. If all the systems were divided into groups of 10, Seattle would rank at the top of the third tier. Given Dipoto's willingness to make moves and he still has veteran assets he could deal, the Mariners could move up a few more notches by the time MLB Pipeline unveils its new organization talent rankings in March.
Here are the four other farm systems that improved the most over the course of 2018:
Astros
Of the five teams we'll mention in this story, the Astros have the best farm system. They possess the top tandem of position and pitching prospects in outfielder Kyle Tucker and right-hander Forrest Whitley, though those two have been in the organization together for a couple of years already.
• Astros Top 30 prospects
Houston traded several intriguing farmhands in July for veteran reinforcements, but the Astros still saw their system stock surge thanks to the emergence of right-handers Josh James (who led the entire Minors in strikeout rate with 13.5 per nine innings), Corbin Martin, Bryan Abreu and Brandon Bielak. Outfielder Seth Beer became the system's second-best position prospect when he signed as a first-rounder in June, then hit .304/.389/.496 while reaching high Class A in his pro debut.

Royals
While the Mariners clearly had the game's worst farm system at the start of 2018, the Royals were in the discussion for second-worst. Kansas City hasn't improved as much as Seattle, but the Royals still made notable gains, starting with a Draft in which they had three first-round picks that turned into two college arms who unexpectedly fell in their laps (Brady Singer, Jackson Kowar) and a third who opened eyes in a stunning pro debut (Daniel Lynch).
• Royals Top 30 prospects
The Royals' Draft extends deeper than that, with left-handers Kris Bubic (supplemental first round) and Austin Cox (fifth) plus outfielder Kyle Isbel (third) already ranking among their best prospects. Several prospects already in the system also boosted their stock, with outfielder Khalil Lee showing all-around tools and outfielder Seuly Matias, catcher MJ Melendez and first baseman Nick Pratto teaming up (along with several draftees) to help low Class A Lexington win the South Atlantic League championship.

Tigers
After sitting in the bottom tier of farm systems for more than a decade, the Tigers have crept close to the top 10. A strong 2018 Draft helped push them upward, beginning with right-hander Casey Mize (the No. 1 overall pick) as well as outfielder Parker Meadows (second round) and second baseman Kody Clemens (third).
• Tigers Top 30 prospects
Detroit also made summer deals to grab shortstop Willi Castro from the Indians and right-hander Logan Shore from the Athletics, then claimed outfielder Dustin Peterson off waivers from the Braves in September. Two trade acquisitions in 2017, shortstop Isaac Paredes and outfielder Daz Cameron, upgraded their standing after reaching Double-A ahead of schedule and performing well there.

Twins
The Twins' system is comparable to that of the Astros, with both ranking close to the top five after just missing the MLB Pipeline Top 10 rankings last March. Shortstop Royce Lewis (the No. 1 overall pick in 2017) and outfielder Alex Kirilloff (a 2016 first-rounder who missed the next year after Tommy John surgery) were highly regarded coming into the year, and they now rank among the most elite prospects in the game. Right-hander Brusdar Graterol vaulted into the Top 100 Prospects list after making his full-season debut.
In terms of new talent, Minnesota grabbed outfielder Trevor Larnach and catcher Ryan Jeffers with their first two selections in the 2018 Draft. The Twins also were active at the Trade Deadline, using veterans to secure five additions to our Twins Top 30 in right-handers Jorge Alcala and Jhoan Duran and outfielders Gilberto Celestino, Gabriel Maciel and Luke Raley.