neo4j-cypher-skill

When to Use

• Writing, optimizing, or debugging Cypher queries
• Graph pattern matching, QPEs, variable-length paths
• Vector/fulltext search, subqueries, batch writes, LOAD CSV

When NOT to Use

• Driver migration/API changes → neo4j-migration-skill
• DB admin (users, config, backups) → neo4j-cli-tools-skill
• Hybrid search that combines vector with fulltext or other ranked sources → neo4j-vector-index-skill

GQL conformance note: LET, FINISH, FILTER, and INSERT are valid Cypher 25 clauses (introduced via GQL conformance, mostly in Neo4j 2025.06). On older versions, fall back to WITH / (omit RETURN) / WHERE / CREATE. INSERT requires &-separated multi-labels and does not support dynamic labels/types.

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Pre-flight

Schema unknown + no tool → produce non-executable sketch outside a code block:

(<SOURCE_LABEL> {<KEY>: $value})-[:<REL_TYPE>]->(<TARGET_LABEL>)

Never fill guessed names — realistic guesses get copied blindly.

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Defaults — apply every query

1. CYPHER 25 — first token; never repeat after UNION or inside subqueries
2. Schema first — inspect before writing; if schema in prompt, use it directly
3. MERGE on constrained key only; rel MERGE on already-bound endpoints only
4. Label-free MATCH (n) forbidden unless bound or followed by WHERE n:$($label)
5. LIMIT 25 default on all exploratory reads; push WITH n LIMIT before high-cardinality operations (variable-length traversals, fan-out MATCH, Cartesian products)
6. Comments: // only — -- is SQL, invalid
7. REPEATABLE ELEMENTS / DIFFERENT RELATIONSHIPS go after MATCH, not end of pattern
8. SHOW commands: YIELD before WHERE; combinable with general Cypher clauses incl. UNION/RETURN [2026.05] — SHOW DATABASES still requires system db (use USE system)
9. Inline node predicates (:Label WHERE p=x) — valid in MATCH only
10. WHERE cannot follow bare UNWIND — use WITH x WHERE
11. (a)-[:R]-(b) — undirected matches both directions, double-counts; use directed unless unknown
12. DETACH DELETE — plain DELETE throws if node has relationships

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Style

Schema is truth. :Person, :KNOWS, name in examples are illustrative — substitute real names from schema.

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Schema-First Protocol

Priority order:

1. <db-name>-schema.json anywhere in project → read directly, state file name + schema_retrieved_at, skip live inspection. If significantly outdated and DB reachable, offer re-fetch. Full rules: references/schema-guardrail.md.

• Existence — labels/rel-types/properties must be in schema; try synonym resolution before asking
• Property type — reason about intent first (e.g. string vs INTEGER may be null check); ask only if unclear
• Relationship direction — wrong direction → correct silently and note
• Synonym mapping — unambiguous → resolve silently; ambiguous → pick most likely, note; ask if unresolvable

Scripts: generate_schema.py (live DB + APOC), define_schema.py (no DB), import_neo4j_schema.py (converts neo4j-graphrag-python, graph-schema-introspector, graph-schema-json-js-utils, mcp-neo4j-data-modeling).

1. Schema in context → use it, skip inspection.

1. Schema missing → run:

CALL db.schema.visualization() YIELD nodes, relationships RETURN nodes, relationships;
SHOW INDEXES YIELD name, type, labelsOrTypes, properties, state WHERE state = 'ONLINE';
SHOW CONSTRAINTS YIELD name, type, labelsOrTypes, properties;
SHOW PROCEDURES YIELD name RETURN split(name,'.')[0] AS namespace, count(*) AS procedures;

Property types per label — check APOC first:

// If APOC available (preferred — use this):
CALL apoc.meta.schema() YIELD value RETURN value;

// No APOC AND database ≤ 100k nodes/rels only (expensive on large graphs):
CALL db.schema.nodeTypeProperties() YIELD nodeType, propertyName, propertyTypes, mandatory;
CALL db.schema.relTypeProperties() YIELD relType, propertyName, propertyTypes, mandatory;

Validate before returning any query: label exists · rel type+direction correct · property on that label · index ONLINE.

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Key Patterns

MERGE

// MERGE on constrained key; set extras in ON CREATE/ON MATCH
CYPHER 25
MATCH (a:Person {id: $a}) MATCH (b:Person {id: $b})
MERGE (a)-[r:KNOWS]->(b)
  ON CREATE SET r.since = date()
  ON MATCH  SET r.lastSeen = date()

SET n = {} replaces all props. SET n += {} merges (safe partial update). Use += for updates.

WITH scope

CYPHER 25
MATCH (a:Person)-[:KNOWS]->(b:Person)
WITH a, count(*) AS friends   // b dropped here
WHERE friends > 5
RETURN a.name, friends ORDER BY friends DESC

Every var not listed in WITH is dropped. WITH * carries all forward.

Subqueries — cheat sheet

EXISTS { (a)-[:R]->(b) }                           // boolean check
COUNT  { (a)-[:R]->(b) WHERE a.x > 0 }             // count
COLLECT { MATCH (a)-[:R]->(b) RETURN b.name }       // collect list (full MATCH+RETURN required)
CALL (p) { MATCH (p)-[:ACTED_IN]->(m) RETURN m }    // correlated subquery (explicit import)
OPTIONAL CALL (p) { ... }                           // nullable subquery

CALL { WITH x ... } deprecated → CALL (x) { ... }. COLLECT {} returns exactly one column.

CALL IN TRANSACTIONS (bulk writes)

CYPHER 25
LOAD CSV WITH HEADERS FROM 'file:///data.csv' AS row
CALL (row) {
  MERGE (p:Person {id: row.id}) SET p += row
} IN TRANSACTIONS OF 1000 ROWS ON ERROR CONTINUE REPORT STATUS AS s

Input stream must be outside subquery. Auto-commit only — never wrap in beginTransaction(). PERIODIC COMMIT deprecated.

QPE basics

CYPHER 25
MATCH SHORTEST 1 (a:Person {name:'Alice'})(()-[:KNOWS]->()){1,}(b:Person {name:'Bob'})
RETURN b.name

// ACYCLIC [2026.03] — no repeated nodes within a path (prevents cycles)
CYPHER 25
MATCH p = ACYCLIC (start:Router {name: $from})-[:LINK]-+(end:Router {name: $to})
RETURN [n IN nodes(p) | n.name] AS route
ORDER BY length(p) LIMIT 5

Quantifier outside group: (pattern){N,M}. Groups start+end with node. REPEATABLE ELEMENTS needs bounded {m,n}. ACYCLIC implies nodes cannot repeat within a path (stronger than default DIFFERENT RELATIONSHIPS).

Match mode — add after MATCH:

• DIFFERENT RELATIONSHIPS (default) — each rel traversed once per path
• REPEATABLE ELEMENTS [2025.x] — nodes/rels revisitable; use for circular routes, weight-optimized paths, constrained backtracking; requires bounded {m,n}

Conditional CALL subqueries [2025.06]

CYPHER 25
MATCH (move:Item {id: $id})
OPTIONAL MATCH (insertBefore:Item {id: $before})
OPTIONAL MATCH (insertAfter:Item  {id: $after})
CALL (move, insertBefore, insertAfter) {
  WHEN insertBefore IS NULL THEN {
    MATCH (last:Item) WHERE NOT (last)-[:NEXT]->() AND last <> move
    CREATE (last)-[:NEXT]->(move)
  }
  WHEN insertAfter IS NULL THEN {
    CREATE (move)-[:NEXT]->(insertBefore)
  }
  ELSE {
    CREATE (insertAfter)-[:NEXT]->(move)
    CREATE (move)-[:NEXT]->(insertBefore)
  }
}

Use WHEN…THEN…ELSE for if-else-if write logic; mutually exclusive (first match wins). Not available pre-2025.06.

Dynamic relationship types [2025.x]

// Create/match/merge with dynamic rel type (must resolve to exactly one STRING)
CYPHER 25 CREATE (a:Node)-[:$($relType)]->(b:Node)
CYPHER 25 MATCH  (a:Node)-[:$($relType)]->(b:Node) RETURN a.name, b.name

Spatial / Point

// WGS84 geographic point
SET n.coords = point({longitude: $lon, latitude: $lat})

// Distance in metres; requires POINT index for performance
MATCH (a:Place {name: $origin}) MATCH (b:Place)
RETURN b.name, point.distance(a.coords, b.coords) AS distM
ORDER BY distM LIMIT 10

// Bounding-box pre-filter (uses POINT index) then distance
MATCH (b:Place)
WHERE point.withinBBox(b.coords,
        point({longitude: $west, latitude: $south}),
        point({longitude: $east, latitude: $north}))
RETURN b.name, point.distance(b.coords, $origin) AS distM

Create POINT index: CREATE POINT INDEX name IF NOT EXISTS FOR (n:Place) ON (n.coords)

Aggregation grouping keys

Non-aggregating expressions in RETURN/WITH are implicit grouping keys — no GROUP BY needed:

// actor + director are grouping keys; count(*) is the aggregate
MATCH (a:Person)-[:ACTED_IN]->(m:Movie)<-[:DIRECTED]-(d:Person)
RETURN a.name, d.name, count(*) AS collaborations
ORDER BY collaborations DESC

count(n) counts non-null; count(*) counts rows including nulls. collect(DISTINCT expr) deduplicates. count() is faster than size(collect()) — count() reads the internal store; collect() builds a list first.

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Common Syntax Traps (top causes of broken queries)

Full trap table → references/syntax-traps.md

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Output Mode and Write Gate

Default: parameterized queries. *Return named properties, not full nodes or RETURN .**

// RIGHT: agent gets named fields it can reason over
CYPHER 25 MATCH (n:Organization {name: $name}) RETURN n.name, n.founded, n.industry LIMIT 10

// WRONG: full node object wastes tokens, leaks all properties, agent can't extract fields cleanly
CYPHER 25 MATCH (n:Organization {name: $name}) RETURN n LIMIT 10

Exception: schema/diagnostic queries (CALL db.schema.visualization(), SHOW INDEXES YIELD *, EXPLAIN) where the object is the point.

Validation workflow:

1. EXPLAIN before any write — catches syntax errors, missing indexes
2. New read: test with LIMIT 1 first
3. Write: verify read half as RETURN before replacing with SET/CREATE/DELETE
4. PROFILE to measure db hits; check for AllNodesScan, CartesianProduct, Eager

Query API v2 (no driver needed — works for schema inspection, EXPLAIN, reads, writes):

curl -X POST https://<instance>.databases.neo4j.io/db/<database>/query/v2 \
  -u <user>:<password> -H "Content-Type: application/json" \
  -d '{"statement": "EXPLAIN MATCH (n:Person {name: $name}) RETURN n", "parameters": {"name": "Alice"}}'
# Local: http://localhost:7474/db/<database>/query/v2
# Response: {"data": {"fields": [...], "values": [...]}}  — prefix EXPLAIN to plan without executing

Write execution gate — only when agent executes (MCP/cypher-shell/HTTP), NOT when generating for code/scripts/user to run:

1. Run EXPLAIN → report estimated rows affected
2. Wait for user confirmation before executing

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Version Gates

Default to 2025.01-safe features when version unknown.

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Performance

EXPLAIN/PROFILE red flags: AllNodesScan CartesianProduct NodeByLabelScan Eager

Fix Eager — three approaches (choose simplest that works):

1. Add specific labels to MATCH nodes to eliminate read/write ambiguity:

MATCH (x:CallingPoint) instead of bare MATCH (x) when writing :City nodes

1. Collect first, then write: WITH collect(u) AS users UNWIND users AS u ...
2. CALL IN TRANSACTIONS: isolates each batch in its own transaction

Label inference — when planner underestimates selectivity on multi-label queries: [Neo4j 5]

CYPHER inferSchemaParts = most_selective_label
MATCH (admin:Administrator {name: $name}), (resource:Resource {name: $res})
MATCH p=(admin)-[:MEMBER_OF]->()-[:ALLOWED_INHERIT]->(company)
RETURN count(p)

Index anchors: every MATCH/MERGE/WHERE on a property needs an index on the lookup property or Neo4j scans all nodes. Index only activates when the node has a label — MATCH (n {prop: $v}) never uses an index; MATCH (n:Label {prop: $v}) does. MERGE without a constraint has no atomicity guarantee (two concurrent MERGEs can create duplicates). CONTAINS/ENDS WITH → TEXT index (RANGE does not support them). Force a plan with USING INDEX n:Label(prop) when EXPLAIN shows a scan. Chained OPTIONAL MATCH for nested data → replace with COLLECT { MATCH ... RETURN }. Dynamic labels ($($label)) → AllNodesScan+Filter; use static labels when possible.

Full anti-patterns → references/performance.md

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Failure Recovery

• 0 results: check param types, remove WHERE predicates one-by-one, EXPLAIN for index use
• TypeErrors: use toIntegerOrNull()/toFloatOrNull(); guard with IS NOT NULL
• Variable out of scope: not listed in WITH → use count(*) not count(droppedVar)
• Timeouts: fix AllNodesScan → add early LIMIT → CALL IN TRANSACTIONS OF 1000 ROWS
• Long-running query progress [2026.03]: SHOW TRANSACTIONS YIELD currentQuery, status, currentQueryProgress
• DateTime mismatch: ZONED DATETIME >= date(...) → 0 rows; use datetime() or .year
• Z suffix ≠ UTC timezone: ISO strings with Z are stored as a UTC-offset, not the UTC zone — range queries across Z and UTC stored values return 0 rows. Coerce on write: datetime({datetime: datetime($isoStr), timezone: 'UTC'})
• Duration: .inDays/.inMonths don't exist; use .days/.months
• Cannot merge node using null property value: MERGE key resolved to null — validate params first
• IndexNotFoundError: SHOW INDEXES YIELD name, state WHERE state <> 'ONLINE'

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References

Load on demand:

• references/indexes.md — index types (RANGE/TEXT/FULLTEXT/POINT/COMPOSITE/LOOKUP), constraints, MERGE lock semantics, fulltext Lucene syntax, import pre-flight
• references/cypher-syntax.md — full syntax reference: WITH, DELETE, ORDER BY, CASE, null, lists, strings, dates, spatial/point, LOAD CSV, subqueries, QPEs, dynamic labels, SEARCH; conditional CALL (WHEN/THEN/ELSE); label pattern expressions; allReduce; NEXT clause; compact CASE WHEN; normalize(); index/constraint types table; functions annotated with version introduced
• references/syntax-traps.md — 40+ syntax trap table
• references/performance.md — anti-patterns, text vs fulltext indexes, Eager (3 fix strategies), label inference, batching best practices, parallel runtime
• references/advanced-patterns.md — REPEATABLE ELEMENTS patterns, allReduce stateful traversal, multi-stop QPE, route planning simulation, DAG critical path, temporal fraud detection component graph, cycle detection, OPTIONAL CALL
• references/apoc.md — APOC Core: refactoring, virtual graph, merge helpers, path expanders, triggers, collections, conditional execution
• references/graph-type.md — PREVIEW (2026.02+) GRAPH TYPE DDL: ALTER CURRENT GRAPH TYPE SET, EXTEND GRAPH TYPE WITH, DROP GRAPH TYPE ELEMENTS, property types, constraints, label implications, relationship type enforcement

WebFetch

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Checklist

• [ ] Schema inspected or confirmed in context
• [ ] CYPHER 25 prefix on every top-level query
• [ ] $parameters used (not literals)
• [ ] LIMIT on exploratory reads (default 25)
• [ ] EXPLAIN run; red flags resolved
• [ ] Write half verified as RETURN before executing
• [ ] Write execution gate applied if agent is executing (not generating)
• [ ] MERGE on constrained key only
• [ ] No label-free MATCH (n)
• [ ] Schema ops not inside explicit transaction