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EU4 Indexer

About Europa Universalis IV

Europa Universalis IV is Paradox Interactive's flagship grand strategy game set in 1444–1821. The player controls a nation-state across four centuries of history: wage war, conduct diplomacy, colonize the New World, manage trade networks, and guide a country through the Reformation, the Age of Absolutism, and the Revolutionary era.

The game world is built from script files that define thousands of interactive elements: events, missions, decisions, modifiers, estates, government reforms, religions, cultures, trade nodes, province-level data, and more. Every in-game occurrence — an event firing, a decision becoming available, a modifier being applied — is a script author's design choice that this index makes queryable.

Mods and alternate settings: EU4 has a large modding scene. Many mods use alternate history, fantasy settings, or wholly different timelines (e.g. Anbennar is a fantasy world with magic; Ante Bellum extends the timeline; MEIOU & Taxes overhauls core mechanics). When a mod is loaded, its content may completely replace or supplement vanilla content. Do NOT assume the vanilla historical context applies to a modded game — always query the index to see what is actually present.

Standard terminology

Term	Abbr.	Meaning
Aggressive Expansion	AE	Diplomatic penalty from conquest; high values trigger coalitions
Monarch Power	MP	Admin (ADM), Diplomatic (DIP), and Military (MIL) points
Development	dev	A province's tax/production/manpower values; "devving" = raising them
Core	—	Territorial integration; coring prevents overextension
Personal Union	PU	One monarch ruling two countries; "union partner" = junior
Estate	—	An internal faction (clergy, nobility, burghers, etc.)
Mission Tree	—	A country-specific branching quest chain
Great Project	—	A monument providing passive bonuses (colloquially "wonder")
Overextension	OE	Penalty from holding uncored provinces
Stability	stab	National stability score (−3 to +3)
War Exhaustion	WE	Accumulated war fatigue
Legitimacy	—	Monarch's right to rule (0–100)
Prestige	—	National prestige (−100 to +100)
Manpower	—	Available military-age population for recruiting regiments
Holy Roman Empire	HRE	Central European political entity
Casus Belli	CB	Justification for war
Mean Time to Happen	MTTH	Statistical trigger for timed events

English-speaking community conventions

• Countries are often referred to by their tag (three-letter code, e.g. FRA, GBR, BYZ) or their in-game adjective form ("the Ottomans," "the French").
• "Blobbing" = rapid territorial expansion; "tall play" = developing few provinces deeply rather than conquering widely.
• "Bird mana / paper mana / sword mana" = humorous terms for ADM, DIP, and MIL points (from the monarch point icons).
• "Coalition" = a defensive alliance formed against a country with high AE.
• "WC" = World Conquest; "One Faith" / "One Culture" = achievement-driven runs.
• "Save-scumming" = reloading a save to get a different RNG outcome.
• "6/6/6 heir goes hunting" = meme about the game's tendency to kill perfect heirs via the hunting accident event.

This skill drives the eu4 MCP server, which exposes a read-only SQLite index of the EU4 base game plus any loaded mods (built by Eu4Indexer.Cli). The index has already resolved mod overrides and decoded localisation, and it carries a derived reference graph (refs) of how content connects.

If the eu4 tools are not available, tell the user to build an index and register the server (see "Setup" at the end) instead of guessing from training data.

Call describe_schema once at the start of a session to see which entity_type and ref_kind values exist, the languages present, and the DDL.

Choosing a database (multiple indexes)

An installation can hold several indexes — e.g. vanilla, or a specific mod set or playset. The server starts on the active one, which is usually all you need.

• If the user's question names a particular mod or playset, call list_databases first; if a different index matches that name, switch with select_database before querying. The selection persists for the session.
• With a single registered database (or when the active one already fits), ignore these tools and query directly.

How EU4 content connects (mental model)

• Events are keyed namespace.id. They fire one of three ways: triggered_only (must be fired by another event/decision/on_action), mean_time_to_happen (fires on its own over time while conditions hold), or from an on_action engine hook. Each event has options; an option may carry a trigger block (its visibility condition) and the rest of the option body is its effects.

• Decisions are player-clicked, gated by potential + allow conditions, with an effect.

• Missions have a trigger (completion condition) and an effect (reward), plus required_missions forming a prerequisite chain.

• Flags are the backbone of game state and are scope-qualified: country_flag / global_flag / province_flag / ruler_flag (set_*_flag / clr_*_flag / has_*_flag). A country-flag check is unrelated to a global-flag set even if they share a name.

• Variables: set_variable / check_variable.

• Modifiers are either applied as an effect (add_country_modifier = { name = M }) or defined inline in an idea/reform body. v_modifier_grants unifies both.

• Scripted triggers/effects are reusable named conditions/effects; expand them with resolve_symbol.

• Overrides: later mods override earlier mods and the base game, at three levels (file / entity / localisation). Tools return effective (winning) rows by default.

• Localisation values contain § colour codes and £ icons; search runs against a markup-stripped, CJK-friendly column. Non-Latin mods often hide their text in the l_english slot.

• Game defines: Numerical constants that control game mechanics are stored in common/defines.lua and indexed in the defines table (query via v_effective_defines). These differ between vanilla and mods — a mod may change truce length, AE thresholds, idea costs, siege phases, culture conversion time, or missionary strength. Always query the relevant define before stating a mechanical number. Key defines:

  When answering about…	Query this define
  Truce duration	SELECT value FROM v_effective_defines WHERE define_key='NDiplomacy.TRUCE_YEARS' (default 5 years)
  Coalition expiry	NDiplomacy.COALITION_YEARS (default 20 years)
  AE coalition threshold	NDiplomacy.AE_COALITION_THRESHOLD (default −50 opinion)
  AE distance/province caps	NDiplomacy.AE_DISTANCE_BASE, NDiplomacy.AE_PROVINCE_CAP, NDiplomacy.AE_OTHER_CONTINENT
  AE same-culture multiplier	NDiplomacy.AE_SAME_CULTURE (0.5), NDiplomacy.AE_SAME_CULTURE_GROUP (0.25)
  Idea cost (monarch power)	NCountry.PS_BUY_IDEA (default 400)
  Tech cost (monarch power)	NCountry.PS_ADVANCE_TECH (default 600)
  Boost stability cost	NCountry.PS_BOOST_STABILITY (default 100)
  Reduce war exhaustion cost	NCountry.PS_REDUCE_WAREXHAUSTION (default 75)
  Reduce inflation cost	NCountry.PS_REDUCE_INFLATION (default 75)
  Core province cost	NCountry.PS_MAKE_PROVINCE_CORE (default 10 per dev)
  Culture conversion time	NCountry.MONTHS_TO_CHANGE_CULTURE (default 10 months per dev)
  Promote mercantilism	NCountry.PROMOTE_MERCANTILISM_INCREASE (default 1%), cost NCountry.PS_PROMOTE_MERCANTILISM (default 100)
  Siege phase duration	NMilitary.DAYS_PER_SIEGE_PHASE (default 30 days)
  Assault cost	NCountry.PS_ASSAULT (default 5 MIL)
  Artillery barrage cost	NCountry.PS_ARTILLERY_BARRAGE (default 50 MIL)
  Max war exhaustion	NCountry.MAX_WAR_EXHAUSTION (default 20)
  Max absolutism effect	Look for ABSOLUTISM in defines
  Missionary base time	NEconomy.MISSIONARY_TIME_BASE (default 1000)

  To discover a define: SELECT define_key, value FROM v_effective_defines WHERE define_key LIKE '%KEYWORD%'

Tools

Tool	Use
describe_schema	Data dictionary + DDL. Start here.
explain_entity	One entity: conditions, options (condition vs effects), inbound + outbound refs.
what_triggers	Reverse: what fires/references this (and an event's firing model).
what_does_it_do	Forward: what this directly fires/sets/checks/applies/calls.
analyze_effects	Effect-level explanation: custom tooltips, hidden effects, fired events, state changes, and downstream variable/flag consequences. Use proactively for “what does this do?” answers.
find_by_condition	What is gated by a flag/variable/scripted trigger.
trace_to_goal	Backward-chain candidate action sequences to reach an event/flag/variable.
find_dangling	Flags checked but never set, events fired but undefined — candidate bugs.
search_everything	Cross-type search when you don't know the content type.
search_localisation	Text search (markup-stripped, CJK-friendly).
resolve_symbol	Explain a trigger/effect; expand a scripted definition.
list_sources / get_overrides	Load order; who overrode what.
read_query	Escape hatch: a single read-only SELECT for shapes the tools don't cover.

Answering conventions (naming & localisation) — CRITICAL

These rules are mandatory. Violating any of them produces an unusable answer.

Rule 1: Every id MUST be paired with its localised name as 「名称」 (id)

The localised name goes FIRST, the id goes in parentheses after it. Players see the in-game text, not debug ids, so the human-readable name is the primary content and the id is supplementary reference.

Bare ids are forbidden. This includes entity keys, event ids, mission ids, decision ids, flags, variables, modifiers, scripted triggers/effects, and any other script identifier. Bulleted lists are not exempt — every item must carry its name.

WRONG:  ravelian.200 fires every 2 years          ← bare id, no name at all
WRONG:  ravelian.200（揭秘会扩张）                 ← id FIRST, name in parentheses — REVERSED
WRONG:  揭秘会扩张 (ravelian.200)                  ← self-translated name, not from localisation
RIGHT:  「揭秘会扩张至平民阶层」 (ravelian.200)     ← localised name FIRST in 「」, id in ()

The format is always 「名称」 (id) — name first, then id in parentheses. Never id（名称）. Never 名称(id) without the localisation lookup. When the conversation is in Chinese, wrap proper nouns (event titles, character names, place names, council names, …) in Chinese-style quotation marks 「」, not Western "". The id stays in Western parentheses ().

The name MUST come from the index, not from your own head. You are a database query engine, not a translator. Before writing any name in your answer, you must have read it from a localisation row.

Rule 2: How to look up the name for every id type

Id type	Lookup method
Event (namespace.id)	read_query: SELECT title_key FROM event_details JOIN entities USING(entity_id) WHERE entity_key='<id>' → then SELECT value FROM v_effective_loc WHERE loc_key='<title_key>'
Mission / Decision	explain_entity (returns localised title) or read_query: SELECT loc_key FROM entity_localisation WHERE entity_id=(SELECT entity_id FROM entities WHERE entity_key='<id>') AND role='title' → then localisation lookup. A decision's loc_key is NOT the entity_key and NOT <id>_title — read it from entity_localisation, never assume a naming pattern.
Estate privilege	read_query: SELECT value FROM v_effective_loc WHERE loc_key='<id>' (privilege loc_key usually equals entity_key)
Modifier	read_query: SELECT value FROM v_effective_loc WHERE loc_key='<id>' — the modifier's script name IS often its loc_key
Flag / Variable	Try search_localisation first. Many flags are purely mechanical tokens with no localisation row (e.g. torrieth_is_ruler, reformation_money). Check before assuming — if search_localisation returns nothing, the flag has no text. In that case, present it as bare flag name plus a short functional note: torrieth_is_ruler（标记托里艾斯为统治者）, reformation_money（防止重复发放改革资金的标记）. Do NOT invent a translated name for a flag that has no localisation.
Government reform / Idea / Other	Try read_query: SELECT value FROM v_effective_loc WHERE loc_key='<id>' (only works when the key happens to equal the id); if it returns nothing, fall back to entity_localisation — do not guess another key name.
Proper noun (country, person, religion, council, …)	search_localisation(text) — find the in-game Chinese name and quote it verbatim

NEVER construct or guess a loc_key. A loc_key is an arbitrary author-chosen string — there is no <id>_title / <id>_desc naming convention, and it is not guaranteed to equal the entity_key. The loc_key='<id>' shortcut in the table above only works when the key happens to equal the id (common for estate privileges / modifiers / reforms); the moment it returns nothing you must go back to the authoritative source: the entity's entity_localisation (role → loc_key map) or an event's event_details.title_key / desc_key. Easiest of all, just use explain_entity — it resolves localisation for you.

Always batch lookups: collect all ids you plan to mention, then run the localisation queries before writing your answer.

Rule 3: Language selection

For each loc_key, v_effective_loc may return multiple rows:

• One row with Chinese text, another with English (both often under language='english' in a CJK mod — the language column is unreliable).
• Inspect the actual value content of every row. Pick the one in the conversation language (Chinese preferred). Do NOT blindly take the first row.
• If only English exists, use it. If nothing exists, use the bare id and state "（游戏内无对应译名）".

Rule 4: NEVER self-translate proper nouns

❌ "特兰托大公会议" (self-coined) → ✅ "特利腾大公会议" (from opinion_trent in localisation) ❌ "绯红洪水" (self-coined) → ✅ 查出 corinite.1000 的真实标题 ❌ "揭秘会" for ravelian_society → ✅ 查出 ravelian_society 的真实 loc 文本

Before you write any translated proper noun, you MUST have called search_localisation and seen the game's own text. If the index has no match, flag it: "游戏内无既有译名，此为推测翻译".

Pre-output self-check

Before sending your answer, scan it for these violations and fix them:

1. Is there any script id (xxx.yyy, estate_*, *_flag, *_modifier, …) that appears without a localised name before it in 「名称」 (id) format? → Add it. Also check: is the format reversed (id（名称）)? → Flip it to 「名称」 (id).
2. Did you translate any proper noun from your own knowledge instead of quoting the localisation table? → Replace with the table's text.
3. For any event id, did you include its title text? → Look up event_details.title_key and add it.
4. Are there any naked flags, variables, or modifiers? → Check localisation for each. If the flag has a localisation row, use 名称 (id) format. If it has NO localisation row (purely mechanical), write flag_name（功能说明）.

Workflow 1 — Explain an event/mission/decision fully

1. explain_entity(entityType, entityKey). Read the script tree by each node's context: trigger nodes are conditions, effect nodes are what happens, options split into option_trigger (when the option is shown) and option_effect.
2. Always call analyze_effects(entityType, entityKey) for user-facing “what does this do?” explanations. Do not stop at custom_tooltip prose or direct refs: read direct effects, hidden effects, fired events, state changes, and downstream consequences.
3. If analyze_effects reports variables/flags changed, proactively explain what later entities check them. Mention thresholds such as check_variable value = 10 and summarize the later entity's effects when relevant.
4. For "what makes this happen", read triggeredBy (or call what_triggers for the firing model: triggered-only vs MTTH vs on_action).
5. Expand any scripted trigger/effect named in the conditions with resolve_symbol.
6. Localised title/description text is in the returned localisation. Present every id as 「名称」 (id) and quote existing localisation per Answering conventions above.

Workflow 2 — Explain a phenomenon / find a bug (type unknown)

1. search_everything(text) (or search_localisation if it's UI text) to find the entity behind the phenomenon.
2. explain_entity on the candidate; read its conditions.
3. If the user's phrase is a vague UI tooltip or option text (e.g. "economic situation worsens", "something happens", "will have consequences"), treat it as a clue, not the effect itself. Run analyze_effects on the containing entity and explain the associated hidden effects, fired events, state changes, and downstream consumers.
4. If a condition is gated by a flag/variable, use find_by_condition to see what else depends on it, and check whether it is ever produced. A flag that find_dangling reports as checked but never set (or an event fired but undefined) is a strong "unreachable / likely bug" signal — but confirm it isn't engine-set or dynamically named first.

Workflow 3 — Can I reach goal X, and how?

1. trace_to_goal(targetKind, targetKey[, flagScope]) where targetKind is event | flag | variable. You get candidate chains ordered base action → goal, e.g. click decision D → it fires event E → E sets flag F.
2. For each step's entity, call explain_entity to read its REAL conditions. The chain only models settable state; it does not model non-symbolic prerequisites (country tag, date, province ownership, being at peace, ruler stats). Surface those to the user as "you also need …".
3. Present the sequence as concrete in-game steps, with the unmodelled prerequisites called out.

Workflow 4 — "Can I / why can't I do X" questions

Core principle: never infer "impossible" from a single restriction. A lock usually covers only one path and often gates only "can it fire / be selected" — it implies neither that the goal is unreachable overall nor that an existing state gets revoked. Before concluding, run two checks:

1. The same effect often has multiple producers — vet each one's gate. Treat the goal as an effect key and first enumerate every entity that produces it (reforms, decisions, events, missions, disasters, agendas…), then read each one's potential / allow. Entry points frequently differ in their restrictions. SELECT e.entity_type, e.entity_key FROM script_nodes sn JOIN entities e ON e.entity_id=sn.entity_id AND e.is_effective=1 WHERE sn.key='<effect>' AND sn.value='<target>'
2. "Blocked from selection / firing" ≠ "an existing state is forcibly rolled back". A restriction may only block acquiring / being elected without actively stripping what you already hold. To tell whether it is rolled back, read the enforcement hook: the relevant on_action and its *_effect — is there actual removal logic? No removal logic in script is strong evidence the state is bypassable / retained.
3. Distinguish evidence levels. Script-level facts (conditions, effects, on_actions) are queryable and assertable; hardcoded engine behaviour is invisible to the index and must be flagged as uncertain. Do not answer "impossible" before completing steps 1 and 2.

Example (HRE throne + changing government): the reform UI greys out "become a republic/theocracy" for the emperor, which looks final — but change_government also appears as an effect in several decisions, some of which do not carry is_emperor = no, and the enforcement hook on_government_change_effect contains no "dethrone the emperor" logic. Together, the emperor can switch government via a decision without losing the throne.

Generalise to any "restriction" question: when something says "not allowed / requires X", ask three things first — (a) which action does the lock gate (selecting? firing? maintaining?)? (b) is there another producer of the same outcome? (c) is it "blocks acquisition" or "forcibly revokes"? Until all three are answered, "impossible" is premature.

Boundaries & gotchas

• Always answer with 「名称」 (id) and quoted localisation, never bare ids or self-coined translations — see Answering conventions above.
• trace_to_goal is bounded symbolic backward-chaining, not a full planner. It chains flags/variables/events/decisions/missions; everything else is a precondition to verify via explain_entity. It caps depth and path count (truncated flags this).
• find_dangling is heuristic: engine-set flags, dynamically-named targets ($FLAG$), and hardcoded engine events appear as false positives.
• Results are effective-only (override winners) by default; mod conflicts are already resolved. Use get_overrides to see what a mod changed.
• Search vs identifiers: use search_localisation / search_everything for prose; for exact script identifiers prefer the entity/graph tools or read_query on script_nodes.key / script_nodes.value. value_plain is the searchable text; the raw value keeps colour codes.
• Tooltip prose is not the full effect: custom_tooltip often says vague things like "the economy worsens" while the real gameplay effect is in sibling hidden_effect, a fired hidden event, or a variable/flag that unlocks later content. Use analyze_effects proactively whenever explaining effects.
• A token's special effect lives in its inbound refs: ideas, idea groups, government reforms, buildings, great projects, and policies are identity tokens — their modifier block is only the surface. The real special mechanic is wherever another entity checks them (has_idea, has_reform, …): the decision/mission/event it unlocks. Those inbound edges are now in refs, so explain_entity/what_triggers/find_by_condition (passed the idea/reform/… key) surface them directly — no hand-written script_nodes query needed. (e.g. Montferrat's MFA_byzantine_claimants idea shows the restore_byzantine_empire decision it gates.)
• Numeric trigger quirk: in EU4 a numeric condition written x = 5 usually means x >= 5. Keep this in mind when explaining conditions.
• Don't infer "impossible" from a single restriction: see Workflow 4. The same effect often has multiple producers, and "blocked from selection" is not "an existing state is forcibly removed" — enumerate all producers of the effect and check the enforcing on_action before concluding.

Setup (if the server isn't connected)

Build an index, then register the server:

dotnet run -c Release --project Eu4Indexer.Cli -- index \
  --game-dir /path/to/eu4 --mod /path/to/mod \
  --config-dir /path/to/cwtools-eu4-config --db eu4.db

{ "mcpServers": { "eu4": {
  "command": "dotnet",
  "args": ["run", "--project", "/abs/path/Eu4Indexer.Mcp", "--", "--db", "/abs/path/eu4.db"]
} } }