diff --git a/doc/README.md b/doc/README.md
index e6acafa..7713141 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -197,6 +197,37 @@ ability_value_usage can be 1 for plain or 2-6 for aoharu stat skill stat scaling
 
 seems to be activate_lot = 1 means wit check, 0 means guaranteed
 
+tag_id is a slash-separated list of numeric IDs that roughly describe all effects relevant to the skill.
+- 101..104 style front, pace, late, end
+- 201..204 distance sprint, mile, medium, long
+- 301..303 timing early, mid, late race
+- 401 affects speed stat or target speed
+- 402 affects stamina stat or hp
+- 403 affects power stat or acceleration
+- 404 affects guts stat
+- 405 affects wit stat or vision
+- 406 is a debuff of any type, or is a main story self-debuff (creeping anxiety, blatant fear), or is Behold Thine Emperor's Divine Might (both own unique and inherited versions are tagged only 406??)
+- 407 modifies gate delay
+- 501..502 turf/dirt
+- 801..812 scenario skill
+
+600 series applies to skills available in global but are only used in jp.
+- 601 ground condition passive
+- 602 weather passive
+- 603 season passive
+- 604 race track passive
+- 605 time of day passive
+- 606 exchange race passive (kawasaki, funabashi, morioka, ooi)
+- 607 distance passive (non/standard)
+- 608 track direction or corner count passive
+- 609 gate position passive
+- 610 ground type passive
+- 611 popularity passive
+- 612 running style passive
+- 613 passive depending on other horses' styles or skills
+- 614 base stat threshold passive
+- 615 mood passive
+
 # races
 
 - group 1, grade: g1 100, g2 200, g3 300, op 400, pre-op 700