How do I install MCP Oracle Database?

Copy the stdio config for Cursor, Claude Desktop, Claude Code, or VS Code on this page. It uses the publisher's install, not a PlugMCP proxy.

Does MCP Oracle Database need an API key?

No required environment variable is listed on this record.

What transport does MCP Oracle Database use?

MCP Oracle Database runs locally over stdio.

When was MCP Oracle Database last checked?

Last checked 2026-10-28. MCP server for Oracle Database. Introspect schemas, run SQL/DML, call PL/SQL, and diagnose performance over STDIO — with safety enforced by Oracle's least-privilege model.

MCP Oracle Database MCP 服务器

English | Español

mcp-oracle-db

An MCP server for Oracle Database, built with Spring Boot and Spring AI.

Let any MCP-compatible client (Claude Desktop, Cursor, Cline, Continue, VS Code, Windsurf, …) introspect an Oracle schema and run SQL — safely.

Why mcp-oracle-db?

Safe by design — the only security barrier is a least-privilege Oracle user. There is no application-layer SQL gate; Oracle itself rejects every CREATE/ALTER/DROP/GRANT/… with ORA-01031.
70 tools across schema introspection, performance diagnostics, index/query advisory, data helpers, DML, explain plan, schema graphs, PL/SQL and system.
No web port — STDIO transport only. No HTTP/SSE server is ever exposed.
Virtual threads — Java 26 virtual threads, a natural fit for blocking JDBC.
No secrets in the repo — credentials come from environment variables.

Who is it for? DBAs, backend developers and AI-assisted workflows that need a local, read-heavy Oracle companion: explore a schema, diagnose performance, preview DML, and let an LLM run ad-hoc SQL without ever risking structural changes.

What it does

Executed

Schema reads — metadata, DDL source, PL/SQL source, sequences, constraints, partitions, performance diagnostics via V$ views.
DML — INSERT, UPDATE, DELETE, MERGE on existing tables.
PL/SQL invocation — call_procedure (requires GRANT EXECUTE on the target).
Metadata comments — COMMENT ON ....

Rejected by Oracle (the least-privilege user has no DDL/DCL privileges)

All structural DDL — all CREATE ... forms, ALTER, DROP, TRUNCATE, RENAME.
All DCL — GRANT, REVOKE, PURGE, FLASHBACK, LOCK TABLE, AUDIT, NOAUDIT, ANALYZE.

Why mcp-oracle-db?
What it does
Requirements
Quickstart
MCP client configuration
Configuration reference
SQL audit log
Architecture
Tools reference
Security model
Testing
Troubleshooting and FAQ
Limitations and notes
Contributing and agent workflow
License

Requirements

JDK 26
Apache Maven 3.9+ (the included mvnw wrapper is enough)
Oracle Database 12c+ (tested against 19c / 23ai drivers)
An MCP client that speaks STDIO (Claude Desktop, Cursor, Cline, Continue, VS Code, Windsurf, …)

Quickstart

1. Create the least-privilege Oracle user

Run db/setup_least_privilege_user.sql as a DBA. Edit the & placeholders first.

# Linux / macOS
sqlplus system/<dba-password>@//<host>:1521/<service> @db/setup_least_privilege_user.sql

:: Windows (cmd / PowerShell)
sqlplus system/<dba-password>@//<host>:1521/<service> @db\setup_least_privilege_user.sql

It creates a user with CREATE SESSION, SELECT_CATALOG_ROLE, and per-object SELECT/INSERT/UPDATE/DELETE grants on the target schema's tables (plus SELECT on views and sequences). It deliberately grants no DDL and no tablespace quota.

2. Configure credentials (environment variables)

Variable	Meaning	Example
`ORACLE_DB_URL`	Thin JDBC URL	`jdbc:oracle:thin:@//db.host:1521/ORCLPDB1`
`ORACLE_DB_USERNAME`	Least-privilege user from step 1	`mcp_user`
`ORACLE_DB_PASSWORD`	That user's password	`s3cret`
`ORACLE_POOL_SIZE`	HikariCP max pool size (optional, default `7`)	`7`

Which schema does the server use? There is no schema setting. In Oracle the schema equals the connected user, so the default schema is the ORACLE_DB_USERNAME you configure. Because the server introspects through the ALL_* views, it can see any schema where that user has grants — pass the desired schema name as a tool parameter (e.g. list_tables(schema="HR")). Which schemas are visible is controlled entirely by the grants in db/setup_least_privilege_user.sql.

3. Build

# Linux / macOS
./mvnw clean package -DskipTests

# Windows (PowerShell)
.\mvnw.cmd clean package -DskipTests

This produces target/mcp-oracle-db-0.0.1-SNAPSHOT.jar (Spring Boot executable jar).

4. Connect your MCP client (STDIO)

The JSON shape below is the de-facto standard used by Claude Desktop, Cursor, Cline, Windsurf and Continue. See MCP client configuration for the exact config-file path per client.

{
  "mcpServers": {
    "oracle-db": {
      "command": "/path/to/jdk/bin/java",
      "args": ["-jar", "/absolute/path/mcp-oracle-db-0.0.1-SNAPSHOT.jar"],
      "env": {
        "ORACLE_DB_URL": "jdbc:oracle:thin:@//db.host:1521/ORCLPDB1",
        "ORACLE_DB_USERNAME": "mcp_user",
        "ORACLE_DB_PASSWORD": "s3cret"
      }
    }
  }
}

Restart the client after saving. Verify with the test_connection tool, which reports the database version, name, current user, current schema and instance.

Quick first session

Once the client shows the server connected, try these in order:

test_connection — confirm reachability and the connected user/schema.
list_tables(schema="HR") — see the tables you can access.
describe_table(schema="HR", table="EMPLOYEES") — columns, types, nullability.
get_sample_data(schema="HR", table="EMPLOYEES") — first N rows, no risk.
run_query(sql="SELECT department_id, COUNT(*) FROM \"HR\".\"EMPLOYEES\" GROUP BY department_id") — ad-hoc SQL, capped by max-rows.

MCP client configuration

All STDIO clients share the same server block shown in step 4. They differ only in where that block is read from:

Client	Config file	Key / notes
Claude Desktop	macOS `~/Library/Application Support/Claude/claude_desktop_config.json` · Windows `%APPDATA%\Claude\claude_desktop_config.json`	`"mcpServers"`
Cursor	`.cursor/mcp.json` (project) or `~/.cursor/mcp.json` (global)	`"mcpServers"`
Cline (VS Code)	`…/globalStorage/saoudrizwan.claude-dev/settings/cline_mcp_settings.json`	`"mcpServers"`, set `"disabled": false`
Windsurf	`~/.codeium/windsurf/mcp_config.json` (Windows: `%USERPROFILE%\.codeium\windsurf\mcp_config.json`)	`"mcpServers"`
Continue	`~/.continue/config.yaml` (or `.continue/config.json` in the repo)	`"mcpServers"`
VS Code (MCP, 1.102+)	`.vscode/mcp.json` in the workspace	uses `"servers"` with `"type": "stdio"`

Paths can change between client versions — when in doubt, check the client's own docs. What matters is that the command / args / env block is identical for all of them.

VS Code note — its schema uses servers instead of mcpServers, and each entry needs "type": "stdio":

{
  "servers": {
    "oracle-db": {
      "type": "stdio",
      "command": "/path/to/jdk/bin/java",
      "args": ["-jar", "/absolute/path/mcp-oracle-db-0.0.1-SNAPSHOT.jar"],
      "env": {
        "ORACLE_DB_URL": "jdbc:oracle:thin:@//db.host:1521/ORCLPDB1",
        "ORACLE_DB_USERNAME": "mcp_user",
        "ORACLE_DB_PASSWORD": "s3cret"
      }
    }
  }
}

Configuration reference

Optional tuning lives in application.yaml under oracle.mcp:

Property	Meaning	Default
`max-rows`	Global cap on rows a `SELECT` returns	`1000`
`query-timeout-seconds`	Per-statement timeout	`120`
`default-sample-rows`	Rows returned by `get_sample_data`	`10`

Logging levels via LOG_LEVEL (default WARN) and APP_LOG_LEVEL (default INFO). Keep in mind that stdout is the JSON-RPC channel — logs go to stderr/file, never stdout.

SQL audit log

Opt-in per-session SQL audit. When enabled, every SQL statement that reaches Oracle is appended to a .txt file — one file per session.

Variable	Meaning	Default
`MCP_AUDIT_ENABLED`	Enable the audit subsystem (`true`/`false`)	`false`
`MCP_AUDIT_DIR`	Directory for audit log files	`./mcp-audit-logs`

Enabling in your MCP client

Add the two variables to the env block of your MCP server entry — this is the only place you need to touch. Example for Claude Desktop / Cursor (claude_desktop_config.json or .cursor/mcp.json):

{
  "mcpServers": {
    "oracle-db": {
      "command": "/path/to/jdk/bin/java",
      "args": ["-jar", "/absolute/path/mcp-oracle-db-0.0.1-SNAPSHOT.jar"],
      "env": {
        "ORACLE_DB_URL": "jdbc:oracle:thin:@//db.host:1521/ORCLPDB1",
        "ORACLE_DB_USERNAME": "mcp_user",
        "ORACLE_DB_PASSWORD": "s3cret",
        "MCP_AUDIT_ENABLED": "true",
        "MCP_AUDIT_DIR": "/var/log/mcp-oracle-db"
      }
    }
  }
}

After saving, restart the client so it relaunches the MCP server with the new environment. One .txt per session is then created in MCP_AUDIT_DIR and appended on every SQL the server launches against Oracle.

To validate quickly without the client, run the jar directly:

# Linux / macOS
MCP_AUDIT_ENABLED=true MCP_AUDIT_DIR=./mcp-audit-logs \
ORACLE_DB_URL=jdbc:oracle:thin:@//host:1521/SVC \
ORACLE_DB_USERNAME=mcp_user ORACLE_DB_PASSWORD=... \
java -jar target/mcp-oracle-db-0.0.1-SNAPSHOT.jar

# Windows (PowerShell) — set env vars in the same shell, then launch
$env:MCP_AUDIT_ENABLED="true"; $env:MCP_AUDIT_DIR="./mcp-audit-logs"
$env:ORACLE_DB_URL="jdbc:oracle:thin:@//host:1521/SVC"
$env:ORACLE_DB_USERNAME="mcp_user"; $env:ORACLE_DB_PASSWORD="..."
java -jar target/mcp-oracle-db-0.0.1-SNAPSHOT.jar

Filename format: <serverName>-<dd-MM-yyyy>-<sessionId8>-log.txt.

Each entry records the tool name, parameters, SQL text, outcome, row count and duration:

===== 2026-06-27T14:30:52.884 =====================================
tool     : get_sample_data
params   : schema=HR, table=EMPLOYEES, rows=10
kind     : Select
type     : READ
sql      : SELECT * FROM "HR"."EMPLOYEES" FETCH FIRST 10 ROWS ONLY
outcome  : OK
rows     : 10
duration : 23 ms
-------------------------------------------------------------------

Notes:

Audit files contain SQL text including literals and parameter values — protect the audit directory.
Disabled by default; zero overhead when off (no files, no I/O).
STDIO-safe — writes to the filesystem only, never to stdout.

Architecture

Strict layering. Dependencies point inward (tools → services → persistence). An audit aspect observes every SQL reaching OracleDataAccess without altering SQL text or results.

flowchart TD
    Client["MCP client<br/>(Claude Desktop, Cursor, Cline, …)"]
    subgraph Server["mcp-oracle-db (Spring Boot · STDIO)"]
        Tools["@McpTool endpoints<br/><i>tools/*Tools.java</i>"]
        Services["Services<br/><i>Metadata · Query · DML · Plsql ·<br/>Performance · IndexAdvisor · Graph · …</i>"]
        Access["OracleDataAccess<br/><i>JdbcTemplate · named-param · callable</i>"]
        Audit["Audit aspects<br/><i>SqlAuditAspect · ToolAuditAspect (MDC)</i>"]
        Tools --> Services --> Access
        Audit -. observes .-> Access
    end
    Oracle[("Oracle DB<br/>least-privilege user<br/>= the only barrier")]
    Client <-->|JSON-RPC over STDIO| Tools
    Access --> Oracle
    Oracle -. "ORA-01031 on DDL/DCL" .-> Access

Tools reference

70 tools, grouped by category. Read-only never modifies data; write executes on the database.

Schema introspection (read-only)

Tool	Description
`list_schemas`	List all Oracle schemas (users) visible to the current connection.
`list_tables`	List tables; optional schema and case-insensitive LIKE name pattern (defaults to `%`).
`list_views`	List views; optional schema and LIKE name pattern.
`describe_table`	Columns of a table: name, data type, nullability, default value and comment. Call before writing SELECT/INSERT/UPDATE against an unverified table.
`list_indexes`	Indexes on a table with their columns, uniqueness and status.
`list_constraints`	Constraints on a table (PK, FK, unique, check) with columns and references.
`list_sequences`	Sequences with range, increment, last number, cycle flag and cache size (from `ALL_SEQUENCES`, not `DBA_SEQUENCES`). Optional schema.
`get_sequence_info`	Metadata for one sequence (range, increment, last number, cache/order flags) from `ALL_SEQUENCES`. Read-only: does NOT consume `NEXTVAL`.
`table_exists`	`true` if a table exists (via `ALL_TABLES`; views not considered). Use instead of `run_query {SELECT 1 FROM ALL_TABLES ...}`.
`list_triggers`	Triggers with type, triggering event, target table and status. Optional schema.
`list_objects`	Database objects; optional schema and object-type filter.
`search_objects`	Search objects by case-insensitive LIKE name pattern; optional type filter.
`get_ddl`	DDL of an object via `DBMS_METADATA`. All 3 params required (`schema`, `name`, `type`); read-only. Types: TABLE, VIEW, INDEX, SEQUENCE, PROCEDURE, FUNCTION, PACKAGE, PACKAGE BODY, TRIGGER, TYPE, SYNONYM, DB LINK.
`describe_plsql`	A PL/SQL object: its arguments and full source code.

Extended introspection (read-only)

Tool	Description
`list_materialized_views`	Materialized views with refresh mode, method, last refresh and staleness.
`list_mview_logs`	Materialized view logs defined on tables. Optional schema.
`list_synonyms`	Private and public synonyms with their resolved target and DB link.
`list_partitions`	Partitions of a partitioned table (name, position, high value, rows, compression).
`list_subpartitions`	Subpartitions of a composite-partitioned table.
`list_ind_partitions`	Partitions of indexes on a table (status, leaf blocks, distinct keys).
`list_db_links`	Database links visible to the current user.
`list_procedures`	Stored procedures, functions, packages and types; optional filters.
`list_types`	User-defined types with typecode, attributes, methods and supertype.
`list_dependencies`	Objects a given object depends on (useful for impact analysis).
`list_invalid_objects`	Objects whose status is Invalid (broken code needing recompile).
`list_external_tables`	External tables with access driver, directory, reject limit and parameters.
`list_directories`	Oracle directory objects and their filesystem paths.
`list_lob_columns`	LOB columns with segment, caching, SECUREFILE flag and retention.
`list_scheduler_jobs`	`DBMS_SCHEDULER` jobs with state, run/failure counts, next run, repeat interval.
`list_scheduler_job_runs`	Recent `DBMS_SCHEDULER` job run details: status, duration, error code.

PL/SQL & optimizer stats (read-only)

Tool	Description
`get_plsql_errors`	Compilation errors of PL/SQL units. Critical for diagnosing broken code.
`get_table_stats`	Optimizer stats for a table (rows, blocks, avg row length, last analyzed).
`get_column_stats`	Optimizer stats for columns (NDV, density, nulls, histogram type).
`get_histogram`	Histogram endpoints for a column (skew and cardinality).
`get_session_privs`	System privileges of the current connection (direct + via roles).
`get_session_roles`	Roles enabled for the current connection, with admin/default flags.

Performance diagnostics (read-only, V$ views)

Tool	Description
`list_active_sessions`	Currently ACTIVE sessions (user, machine, program, elapsed). Optional filters.
`list_blocked_sessions`	Sessions currently blocked, with the blocker and the wait event.
`list_locks`	DML/transaction/user locks held and requested, with locked object and mode.
`get_session_sql_text`	Full SQL text being executed by a session (sid, serial#).
`list_top_sql`	Top-N SQL ordered by buffer_gets / disk_reads / elapsed / executions / cpu.
`get_wait_events`	Current wait events from `V$SESSION_WAIT`. Optional sid and wait-class filters.
`get_session_longops`	Long-running operations with progress % and ETA. Optional sid.
`get_instance_info`	Instance info: name, host, version, startup time, status.
`get_database_info`	Database info: name, log mode, open mode, role, flashback status.
`get_system_stats`	Cumulative system statistics from `V$SYSSTAT`.
`get_db_time_model`	Time model from `V$SYS_TIME_MODEL` (DB CPU, DB time, parse time).
`get_parameter`	Initialization parameters from `V$PARAMETER`. Optional name LIKE pattern.
`list_datafile_io`	Datafiles with size, physical reads/writes and average IO time.

Index & query advisory (read-only)

Tool	Description
`list_unused_indexes`	Indexes with columns and best-effort usage (`likely_unused` YES/NO/UNKNOWN). A DBA must run `ALTER INDEX ... MONITORING USAGE` for a definitive answer.
`suggest_index`	Analyse SQL via `EXPLAIN PLAN`; propose a `CREATE INDEX` as text (never executed). Apply manually only after DBA review.
`run_sql_tuning_advisor`	Run `DBMS_SQLTUNE` and return its TEXT report. Requires the `ADVISOR` privilege (see setup script, section 8); otherwise returns guidance.

Data helpers (read / detect)

Tool	Description
`count_rows`	Total row count of a table — the right tool for this; do NOT use `run_query`. No predicate (no hidden SQL surface). For a filtered count use `run_query` with `SELECT COUNT(*) ... WHERE ...`.
`get_next_sequence_value`	`NEXTVAL` of a sequence. Side-effecting: advances the counter and the value cannot be reused. When `cache_size` > 0, verify the returned value is not already present in the target table.
`validate_fk_integrity`	Orphan rows violating FK(s) on a table; orphan count per FK (0 = OK).
`find_duplicates`	Duplicate rows grouped by columns, with counts. Optional minimum count.
`find_free_id`	Smallest free positive id (1..maxRange) not present in a table.column; optional `excludeTable` checks a 2nd table (FK scenarios). Returns `null` if the range is full.

SQL & data (executes on the DB)

Tool	Description
`run_query`	Run a single `SELECT` (capped by `max-rows`; optional `offset`/`limit` for pagination). `CONNECT BY`/`WITH` (CTE) may be rejected by the parser; prefer `MINUS` or client-side compute.
`execute_dml`	Run a single `INSERT`/`UPDATE`/`DELETE`/`MERGE` and auto-commit; returns rows affected. One statement per call (no PL/SQL blocks, multi-statement, or DDL).
`execute_dml_preview`	Non-executing dry-run for `UPDATE`/`DELETE` — row count + sample rows that would be affected.
`execute_dml_rollback_first`	Execute the DML inside a transaction that is immediately rolled back; returns the real row count without persisting.
`get_sample_data`	Preview the first N rows of a table.
`explain_plan`	Return the Oracle execution plan via `DBMS_XPLAN`. Needs a `PLAN_TABLE`.

Schema impact graph (read-only)

Tool	Description
`get_fk_graph`	Foreign-key relationships for a schema (or one table) as JSON edges + Mermaid diagram.
`get_dependency_graph`	Object dependency graph (objects that reference or are referenced by a name) as JSON + Mermaid.

Metadata comments (write)

Tool	Description
`comment_on_table`	Add/replace the comment on a table (own schema).
`comment_on_column`	Add/replace the comment on a column (own schema).

System

Tool	Description
`test_connection`	Verify connectivity; report version, name, user, schema and instance.
`oracle_mcp_health_report`	Five independent readiness probes (connectivity, version, catalog role, invalid objects, server config); aggregate `UP` / `DEGRADED` / `DOWN`.

MCP resources (URI-addressable, read-only)

URI	Returns
`oracle://schema/{schema}/table/{table}`	Column-level description (name, type, nullability, default, comment).
`oracle://schema/{schema}/object/{object}/ddl`	DDL source (type auto-detected — table, view, package, procedure, etc.).
`oracle://schema/{schema}/plsql/{object}`	PL/SQL source code.
`oracle://audit/session/{id}`	Per-session SQL audit log (`id` = 8-char hex; use `current` for the live session).

MCP prompts (guidance templates)

Name	Purpose
`review-sql-performance`	Structured performance review of a SQL statement.
`explain-schema`	Guided exploration of an Oracle schema (tables, columns, relationships, key objects).
`debug-invalid-plsql`	Diagnose broken PL/SQL — invalid objects, error codes, source locations.
`safe-dml-plan`	Plan a DML change safely (pre-flight, dry-run, post-execution).
`data-quality-audit`	Audit data quality (completeness, uniqueness, referential integrity, validity).
`oracle-sql-style`	The server's canonical Oracle SQL authoring rules — prevents common parse errors (ORA-00923/00936/00904/00911/00933).

MCP completions (URI / prompt argument autocompletion)

13 completions total — schema names (6), table names (3), object names (3), and audit session IDs (1). Limited by the MCP spec to resource URI variables and prompt arguments.

Security model

Single-layer security: the least-privilege Oracle user is the only barrier. There is no application-layer SQL gate — SqlGuard was removed deliberately. Every statement a tool sends is executed verbatim against Oracle, and Oracle's privilege model decides allow/deny.

The server connects as a dedicated Oracle user with CREATE SESSION + SELECT_CATALOG_ROLE + per-object SELECT/INSERT/UPDATE/DELETE grants, EXECUTE on specific procedures and packages (à la carte), and no DDL/DCL privileges or tablespace quota. Any CREATE/ALTER/DROP/GRANT/REVOKE/ TRUNCATE/… returns an Oracle error (typically ORA-01031: insufficient privileges) which surfaces to the client as an explanatory message.

 AI SQL  ──▶  OracleDataAccess  ──▶  Oracle (least-priv user)
                     │                       │
                     │              Oracle enforces allow/deny
                     │              (ORA-01031 on DDL/DCL)
                     ▼                       ▼
                result / error string returned to MCP client

All internal metadata queries use ALL_* views with named parameters (:param). Identifiers are validated and double-quoted (see SqlIdentifiers). One statement per tool call — batches are rejected.

Testing

The suite is layered so the bulk runs on every commit with no database required, and the live-Oracle path is opt-in.

Tier 1 — unit + smoke (every ./mvnw test, no DB). Tests across SqlIdentifiers, IndexAdvisor, Graph, SystemService health, AuditLog reader + writer, every tool / resource / prompt / completion, plus McpOracleDbApplicationSmokeTest which boots the full Spring context on an in-memory H2 (Oracle-compat) datasource and asserts all 70 @McpTool endpoints register across the 11 tool hosts. Startup regressions (a bad logback config, a missing bean, a broken auto-config) are caught here.

Tier 2 — end-to-end MCP STDIO harness (opt-in, needs Oracle). McpStdioE2ETest spawns the built jar as a subprocess, performs the real MCP initialize handshake, lists tools, and runs SELECT-only checks (describe_table, run_query, count_rows) over each table you configure, then asserts Oracle rejects CREATE TABLE (insufficient privileges). It is dual-gated so it never runs by accident:

Copy src/test/resources/application-e2e.example.yaml to application-e2e.yaml (gitignored) and fill in the jar path, Oracle credentials, schema and a tables: [...] array.

Run with the mcp-e2e profile:

# Linux / macOS
./mvnw test -Pmcp-e2e          # or run-e2e.bat on Windows (builds the jar first)

# Windows (PowerShell)
.\mvnw.cmd test -Pmcp-e2e

Env-gated integration test. The full context/integration test (McpOracleDbApplicationTests.contextLoads) runs only when ORACLE_DB_URL is set, so ./mvnw test is green without a database.

ORACLE_DB_URL=... ORACLE_DB_USERNAME=... ORACLE_DB_PASSWORD=... ./mvnw test

Troubleshooting and FAQ

ORA-01031: insufficient privileges when running CREATE/ALTER/DROP/GRANT. This is by design, not a bug. The least-privilege user has no DDL/DCL privileges and no tablespace quota, so Oracle rejects the statement. If you genuinely need structural changes, run them as a DBA — do not widen the MCP user's grants (see Security model).

ORA-12541: TNS:no listener / ORA-12514: TNS:listener … service. The JDBC URL in ORACLE_DB_URL is wrong or the DB is unreachable. Check the host, port and service name. Prefer the EZ-connect form jdbc:oracle:thin:@//host:1521/SERVICE (no tnsnames.ora needed).

The client shows the server "failed to start" / no output. stdout is the JSON-RPC channel — any stray System.out print corrupts framing. The server disables the Spring banner (spring.main.banner-mode= off) for this reason; if you fork the config, keep it off. Logs go to stderr/file only.

explain_plan returns an Oracle error. It needs write access to a PLAN_TABLE. Grant it (see the optional line in db/setup_least_privilege_user.sql, section 5) or skip the tool.

Pool exhaustion / hangs after a DB restart. HikariCP is configured with Oracle JDBC socket timeouts (oracle.jdbc.readTimeout) precisely to recycle dead connections. If you override application.yaml, keep a read-timeout greater than query-timeout-seconds but below the MCP request-timeout (150s).

Which schema does the server introspect? There is no schema setting — the default schema is ORACLE_DB_USERNAME. Pass any accessible schema as a tool parameter (e.g. describe_table(schema="HR", table="EMPLOYEES")). Visibility is bounded by the grants in the setup script.

Can I run multiple SQL statements in one call? No — one statement per tool call. Batches, PL/SQL blocks and ;-chains are rejected. This keeps the execution model predictable and the connection pool healthy.

Limitations and notes

STDIO transport only (local use). No HTTP/SSE server is exposed.
explain_plan needs write access to a PLAN_TABLE (see the optional grant in the setup script). Without it, that tool returns the Oracle error.
One statement per tool call — batches are rejected.
Read access is bounded by what the least-privilege user can see in the ALL_* views.
JSqlParser 4.9 is best-effort only — it labels DML kind in DmlService (INSERT/UPDATE/DELETE/MERGE, else UNKNOWN). It no longer gates anything; Oracle is authoritative.
Oracle JDBC: the BOM is com.oracle.database.jdbc:ojdbc-bom:23.26.2.0.0. orai18n is not on Central under that group — it is omitted; ojdbc17 alone works.

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