Does SQL Developer automatically synchronize metadata after external schema changes?

Short answer

No. Oracle SQL Developer does not automatically synchronize the Connections navigator or object browser after schema changes made by other clients, and there is no preference to set a metadata re-validation interval. The navigator tree is populated on demand when you expand a node and then cached; nothing in the IDE polls the data dictionary in the background or subscribes to DDL events. The refresh model is user-driven, not timer-driven.

What is confirmed vs. likely

Confirmed behavior: the supported remedy is manual. Right-click the connection or the specific object node (Tables, a single table, Indexes, etc.) and choose Refresh. Disconnecting and reconnecting the connection also forces metadata to be re-read from the dictionary.

Likely explanation for the staleness you describe: the tree renders from its cached snapshot, so columns or indexes dropped via SQL*Plus or another IDE remain visible until you refresh. This is a display-layer issue only. Query execution always goes against the live data dictionary, so stale UI metadata never changes actual SQL results — it only misleads your eyes and the completion popups.

Code completion is a separate cache

Completion Insight maintains its own cache of schema, table, and column names, independent of the navigator tree. The relevant settings live under Tools > Preferences > Code Editor > Completion Insight (enable/disable, popup timing). Consequences:

• Refreshing the navigator tree does not necessarily update completion suggestions, and vice versa.
• Dropped or renamed columns can keep appearing in popups. Treat suggestions as hints, not dictionary truth.
• There is no documented "cache size" knob that controls synchronization of UI-bound schema components; the preferences govern insight behavior, not tree refresh.

How to verify the live state

When the UI looks stale, don't trust the tree — query the dictionary directly:

SELECT column_name, data_type
FROM user_tab_columns
WHERE table_name = 'YOUR_TABLE'
ORDER BY column_id;

SELECT object_name, status, last_ddl_time
FROM user_objects
WHERE object_name = 'YOUR_TABLE';

LAST_DDL_TIME is a quick way to confirm whether an external client's DDL actually landed.

Empirical test for your version

1. Open the table node in SQL Developer and note the columns shown.
2. In a second client (e.g., SQL*Plus), run ALTER TABLE your_table ADD (probe_col NUMBER);
3. Back in SQL Developer, confirm the new column is absent from the tree.
4. Right-click the table node > Refresh, and confirm it appears.

Note that cache behavior and preference labels have varied across releases (notably pre-4.x versus later versions), so confirm menu names against your installed version's help. Also, this concerns the IDE's navigator — SQL Developer Data Modeler's model synchronization is a different feature entirely.