diff --git a/src/platform/packages/shared/kbn-esql-ast/src/parser/__tests__/rrf.test.ts b/src/platform/packages/shared/kbn-esql-ast/src/parser/__tests__/rrf.test.ts
new file mode 100644
index 0000000000000..399afe477abbc
--- /dev/null
+++ b/src/platform/packages/shared/kbn-esql-ast/src/parser/__tests__/rrf.test.ts
@@ -0,0 +1,68 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { parse } from '../parser';
+
+describe('RRF', () => {
+  describe('correctly formatted', () => {
+    it('can parse RRF command without modifiers', () => {
+      const text = `FROM search-movies METADATA _score, _id, _index
+                    | FORK
+                      ( WHERE semantic_title:"Shakespeare" | SORT _score)
+                      ( WHERE title:"Shakespeare" | SORT _score)
+                    | RRF
+                    | KEEP title, _score`;
+
+      const { root, errors } = parse(text);
+
+      expect(errors.length).toBe(0);
+      expect(root.commands[2]).toMatchObject({
+        type: 'command',
+        name: 'rrf',
+        args: [],
+      });
+    });
+  });
+
+  describe('when incorrectly formatted, return errors', () => {
+    it('when no pipe after', () => {
+      const text = `FROM search-movies METADATA _score, _id, _index
+                      | FORK
+                        ( WHERE semantic_title:"Shakespeare" | SORT _score)
+                        ( WHERE title:"Shakespeare" | SORT _score)
+                      | RRF KEEP title, _score`;
+
+      const { errors } = parse(text);
+
+      expect(errors.length > 0).toBe(true);
+    });
+
+    it('when no pipe between FORK and RRF', () => {
+      const text = `FROM search-movies METADATA _score, _id, _index
+                    | FORK
+                      ( WHERE semantic_title:"Shakespeare" | SORT _score)
+                      ( WHERE title:"Shakespeare" | SORT _score) RRF`;
+
+      const { errors } = parse(text);
+
+      expect(errors.length > 0).toBe(true);
+    });
+
+    it('when RRF is invoked with arguments', () => {
+      const text = `FROM search-movies METADATA _score, _id, _index
+                    | FORK ( WHERE semantic_title:"Shakespeare" | SORT _score)
+                              ( WHERE title:"Shakespeare" | SORT _score)
+                    | RRF text`;
+
+      const { errors } = parse(text);
+
+      expect(errors.length > 0).toBe(true);
+    });
+  });
+});
diff --git a/src/platform/packages/shared/kbn-esql-ast/src/parser/esql_ast_builder_listener.ts b/src/platform/packages/shared/kbn-esql-ast/src/parser/esql_ast_builder_listener.ts
index e92b154339133..aad759c5c4a90 100644
--- a/src/platform/packages/shared/kbn-esql-ast/src/parser/esql_ast_builder_listener.ts
+++ b/src/platform/packages/shared/kbn-esql-ast/src/parser/esql_ast_builder_listener.ts
@@ -32,6 +32,7 @@ import {
   type TimeSeriesCommandContext,
   type WhereCommandContext,
   RerankCommandContext,
+  RrfCommandContext,
 } from '../antlr/esql_parser';
 import { default as ESQLParserListener } from '../antlr/esql_parser_listener';
 import type { ESQLAst } from '../types';
@@ -351,6 +352,20 @@ export class ESQLAstBuilderListener implements ESQLParserListener {
     this.ast.push(command);
   }
 
+  /**
+   * Exit a parse tree produced by `esql_parser.rrfCommand`.
+   *
+   * Parse the RRF (Reciprocal Rank Fusion) command:
+   *
+   * RRF
+   *
+   * @param ctx the parse tree
+   */
+  exitRrfCommand(ctx: RrfCommandContext): void {
+    const command = createCommand('rrf', ctx);
+    this.ast.push(command);
+  }
+
   enterEveryRule(ctx: ParserRuleContext): void {
     // method not implemented, added to satisfy interface expectation
   }
diff --git a/src/platform/packages/shared/kbn-esql-ast/src/pretty_print/__tests__/basic_pretty_printer.test.ts b/src/platform/packages/shared/kbn-esql-ast/src/pretty_print/__tests__/basic_pretty_printer.test.ts
index 36f5810a06c9c..83dae2c4821c7 100644
--- a/src/platform/packages/shared/kbn-esql-ast/src/pretty_print/__tests__/basic_pretty_printer.test.ts
+++ b/src/platform/packages/shared/kbn-esql-ast/src/pretty_print/__tests__/basic_pretty_printer.test.ts
@@ -235,6 +235,32 @@ describe('single line query', () => {
         );
       });
     });
+
+    describe('RRF', () => {
+      test('from single line', () => {
+        const { text } =
+          reprint(`FROM search-movies METADATA _score, _id, _index | FORK (WHERE semantic_title : "Shakespeare" | SORT _score) (WHERE title : "Shakespeare" | SORT _score) | RRF | KEEP title, _score
+        `);
+
+        expect(text).toBe(
+          'FROM search-movies METADATA _score, _id, _index | FORK (WHERE semantic_title : "Shakespeare" | SORT _score) (WHERE title : "Shakespeare" | SORT _score) | RRF | KEEP title, _score'
+        );
+      });
+
+      test('from multiline', () => {
+        const { text } = reprint(`FROM search-movies METADATA _score, _id, _index
+  | FORK
+    (WHERE semantic_title : "Shakespeare" | SORT _score)
+    (WHERE title : "Shakespeare" | SORT _score)
+  | RRF
+  | KEEP title, _score
+          `);
+
+        expect(text).toBe(
+          'FROM search-movies METADATA _score, _id, _index | FORK (WHERE semantic_title : "Shakespeare" | SORT _score) (WHERE title : "Shakespeare" | SORT _score) | RRF | KEEP title, _score'
+        );
+      });
+    });
   });
 
   describe('expressions', () => {
diff --git a/src/platform/packages/shared/kbn-esql-ast/src/visitor/contexts.ts b/src/platform/packages/shared/kbn-esql-ast/src/visitor/contexts.ts
index 4ddfe95430178..721d11a04dfba 100644
--- a/src/platform/packages/shared/kbn-esql-ast/src/visitor/contexts.ts
+++ b/src/platform/packages/shared/kbn-esql-ast/src/visitor/contexts.ts
@@ -520,6 +520,12 @@ export class ForkCommandVisitorContext<
   Data extends SharedData = SharedData
 > extends CommandVisitorContext<Methods, Data, ESQLAstCommand> {}
 
+// RRF
+export class RrfCommandVisitorContext<
+  Methods extends VisitorMethods = VisitorMethods,
+  Data extends SharedData = SharedData
+> extends CommandVisitorContext<Methods, Data, ESQLAstCommand> {}
+
 // Expressions -----------------------------------------------------------------
 
 export class ExpressionVisitorContext<
diff --git a/src/platform/packages/shared/kbn-esql-ast/src/visitor/global_visitor_context.ts b/src/platform/packages/shared/kbn-esql-ast/src/visitor/global_visitor_context.ts
index 580d293d0c86f..45c3f3619ed1a 100644
--- a/src/platform/packages/shared/kbn-esql-ast/src/visitor/global_visitor_context.ts
+++ b/src/platform/packages/shared/kbn-esql-ast/src/visitor/global_visitor_context.ts
@@ -197,6 +197,10 @@ export class GlobalVisitorContext<
         if (!this.methods.visitForkCommand) break;
         return this.visitForkCommand(parent, commandNode, input as any);
       }
+      case 'rrf': {
+        if (!this.methods.visitRrfCommand) break;
+        return this.visitRrfCommand(parent, commandNode, input as any);
+      }
     }
     return this.visitCommandGeneric(parent, commandNode, input as any);
   }
@@ -417,6 +421,15 @@ export class GlobalVisitorContext<
     return this.visitWithSpecificContext('visitForkCommand', context, input);
   }
 
+  public visitRrfCommand(
+    parent: contexts.VisitorContext | null,
+    node: ESQLAstCommand,
+    input: types.VisitorInput<Methods, 'visitRrfCommand'>
+  ): types.VisitorOutput<Methods, 'visitRrfCommand'> {
+    const context = new contexts.RrfCommandVisitorContext(this, node, parent);
+    return this.visitWithSpecificContext('visitRrfCommand', context, input);
+  }
+
   // #endregion
 
   // #region Expression visiting -------------------------------------------------------
diff --git a/src/platform/packages/shared/kbn-esql-ast/src/visitor/types.ts b/src/platform/packages/shared/kbn-esql-ast/src/visitor/types.ts
index 942141f67fe85..25e5df0bda2ec 100644
--- a/src/platform/packages/shared/kbn-esql-ast/src/visitor/types.ts
+++ b/src/platform/packages/shared/kbn-esql-ast/src/visitor/types.ts
@@ -189,6 +189,7 @@ export interface VisitorMethods<
   >;
   visitForkCommand?: Visitor<contexts.ForkCommandVisitorContext<Visitors, Data>, any, any>;
   visitCommandOption?: Visitor<contexts.CommandOptionVisitorContext<Visitors, Data>, any, any>;
+  visitRrfCommand?: Visitor<contexts.RrfCommandVisitorContext<Visitors, Data>, any, any>;
   visitExpression?: Visitor<contexts.ExpressionVisitorContext<Visitors, Data>, any, any>;
   visitSourceExpression?: Visitor<
     contexts.SourceExpressionVisitorContext<Visitors, Data>,
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/__tests__/helpers.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/__tests__/helpers.ts
index f655491a13c2b..ff33a8dc41a01 100644
--- a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/__tests__/helpers.ts
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/__tests__/helpers.ts
@@ -12,6 +12,12 @@ import type { IndexAutocompleteItem } from '@kbn/esql-types';
 import { ESQLFieldWithMetadata } from '../validation/types';
 import { fieldTypes } from '../definitions/types';
 import { ESQLCallbacks } from '../shared/types';
+import { METADATA_FIELDS } from '../shared/constants';
+
+export const metadataFields: ESQLFieldWithMetadata[] = METADATA_FIELDS.map((field) => ({
+  name: field,
+  type: 'keyword',
+}));
 
 export const fields: ESQLFieldWithMetadata[] = [
   ...fieldTypes.map((type) => ({ name: `${camelCase(type)}Field`, type })),
@@ -107,6 +113,9 @@ export function getCallbackMocks(): ESQLCallbacks {
         };
         return [field];
       }
+      if (/METADATA/i.test(query)) {
+        return [...fields, ...metadataFields];
+      }
       return fields;
     }),
     getSources: jest.fn(async () =>
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/__tests__/autocomplete.command.rff.test.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/__tests__/autocomplete.command.rff.test.ts
new file mode 100644
index 0000000000000..fedbac1df9bdf
--- /dev/null
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/__tests__/autocomplete.command.rff.test.ts
@@ -0,0 +1,53 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { setup } from './helpers';
+
+jest.mock('../../definitions/commands', () => {
+  const actual = jest.requireActual('../../definitions/commands');
+  const modifiedDefinitions = actual.commandDefinitions.map((def: any) =>
+    def.name === 'rrf' ? { ...def, hidden: false } : def
+  );
+  return {
+    ...actual,
+    commandDefinitions: modifiedDefinitions,
+  };
+});
+
+describe('autocomplete.suggest', () => {
+  describe('RRF', () => {
+    it('does not suggest RRF in the general list of commands', async () => {
+      const { suggest } = await setup();
+      const suggestedCommands = (await suggest('FROM index | /')).map((s) => s.text);
+      expect(suggestedCommands).not.toContain('RRF ');
+    });
+
+    it('suggests RRF immediately after a FORK command', async () => {
+      const { suggest } = await setup();
+      const suggestedCommands = (await suggest('FROM a | FORK (LIMIT 1) (LIMIT 2) | /')).map(
+        (s) => s.text
+      );
+      expect(suggestedCommands).toContain('RRF ');
+    });
+
+    it('does not suggests RRF if FORK is not immediately before', async () => {
+      const { suggest } = await setup();
+      const suggestedCommands = (
+        await suggest('FROM a | FORK (LIMIT 1) (LIMIT 2) | LIMIT 1 | /')
+      ).map((s) => s.text);
+      expect(suggestedCommands).not.toContain('RRF ');
+      expect(suggestedCommands).toContain('LIMIT ');
+    });
+
+    it('suggests pipe after complete command', async () => {
+      const { assertSuggestions } = await setup();
+      await assertSuggestions('FROM a | FORK (LIMIT 1) (LIMIT 2) | RRF /', ['| ']);
+    });
+  });
+});
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/autocomplete.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/autocomplete.ts
index 1b24fdd0125e1..adb81c1f9e53d 100644
--- a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/autocomplete.ts
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/autocomplete.ts
@@ -118,8 +118,9 @@ export async function suggest(
 
   if (astContext.type === 'newCommand') {
     // propose main commands here
+    // resolve particular commands suggestions after
     // filter source commands if already defined
-    const suggestions = getCommandAutocompleteDefinitions(getAllCommands());
+    let suggestions = getCommandAutocompleteDefinitions(getAllCommands());
     if (!ast.length) {
       // Display the recommended queries if there are no commands (empty state)
       const recommendedQueriesSuggestions: SuggestionRawDefinition[] = [];
@@ -144,6 +145,12 @@ export async function suggest(
       return [...sourceCommandsSuggestions, ...recommendedQueriesSuggestions];
     }
 
+    // If the last command is not a FORK, RRF should not be suggested.
+    const lastCommand = root.commands[root.commands.length - 1];
+    if (lastCommand.name !== 'fork') {
+      suggestions = suggestions.filter((def) => def.label !== 'RRF');
+    }
+
     return suggestions.filter((def) => !isSourceCommand(def));
   }
 
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/commands/rrf/index.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/commands/rrf/index.ts
new file mode 100644
index 0000000000000..63532cd92e0a9
--- /dev/null
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/autocomplete/commands/rrf/index.ts
@@ -0,0 +1,15 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import type { SuggestionRawDefinition } from '../../types';
+import { pipeCompleteItem } from '../../complete_items';
+
+export function suggest(): SuggestionRawDefinition[] {
+  return [pipeCompleteItem];
+}
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/commands.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/commands.ts
index caf3834806e5f..a28b2c2354f2e 100644
--- a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/commands.ts
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/commands.ts
@@ -69,6 +69,8 @@ import {
   suggest as suggestForRename,
   fieldsSuggestionsAfter as fieldsSuggestionsAfterRename,
 } from '../autocomplete/commands/rename';
+import { suggest as suggestForRrf } from '../autocomplete/commands/rrf';
+import { validate as validateRrf } from '../validation/commands/rrf';
 import { suggest as suggestForRow } from '../autocomplete/commands/row';
 import { suggest as suggestForShow } from '../autocomplete/commands/show';
 import { suggest as suggestForSort } from '../autocomplete/commands/sort';
@@ -706,4 +708,17 @@ export const commandDefinitions: Array<CommandDefinition<any>> = [
 
     fieldsSuggestionsAfter: fieldsSuggestionsAfterFork,
   },
+  {
+    hidden: true,
+    preview: true,
+    name: 'rrf',
+    description: i18n.translate('kbn-esql-validation-autocomplete.esql.definitions.rrfDoc', {
+      defaultMessage:
+        'Combines multiple result sets with different scoring functions into a single result set.',
+    }),
+    declaration: `RRF`,
+    examples: ['… FORK (LIMIT 1) (LIMIT 2) | RRF'],
+    suggest: suggestForRrf,
+    validate: validateRrf,
+  },
 ];
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/types.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/types.ts
index 5b11b3ce4ae0c..78db4231d56a5 100644
--- a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/types.ts
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/definitions/types.ts
@@ -6,13 +6,14 @@
  * your election, the "Elastic License 2.0", the "GNU Affero General Public
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
-import type {
+import {
   ESQLAstItem,
   ESQLCommand,
   ESQLFunction,
   ESQLMessage,
   ESQLSource,
   ESQLAstCommand,
+  ESQLAst,
 } from '@kbn/esql-ast';
 import { ESQLControlVariable } from '@kbn/esql-types';
 import { GetColumnsByTypeFn, SuggestionRawDefinition } from '../autocomplete/types';
@@ -419,7 +420,11 @@ export interface CommandDefinition<CommandName extends string> {
    * prevent the default behavior. If you need a full override, we are currently
    * doing those directly in the validateCommand function in the validation module.
    */
-  validate?: (command: ESQLCommand<CommandName>, references: ReferenceMaps) => ESQLMessage[];
+  validate?: (
+    command: ESQLCommand<CommandName>,
+    references: ReferenceMaps,
+    ast: ESQLAst
+  ) => ESQLMessage[];
 
   /**
    * This method is called to load suggestions when the cursor is within this command.
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/__tests__/test_suites/validation.command.rrf.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/__tests__/test_suites/validation.command.rrf.ts
new file mode 100644
index 0000000000000..c105c7c16e4d0
--- /dev/null
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/__tests__/test_suites/validation.command.rrf.ts
@@ -0,0 +1,70 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import * as helpers from '../helpers';
+
+export const validationRrfCommandTestSuite = (setup: helpers.Setup) => {
+  describe('validation', () => {
+    describe('command', () => {
+      describe('RRF', () => {
+        test('no errors for valid command', async () => {
+          const { expectErrors } = await setup();
+
+          await expectErrors(
+            `FROM index METADATA _id, _score, _index
+                    | FORK
+                      (WHERE keywordField != "" | LIMIT 100)
+                      (SORT doubleField ASC NULLS LAST)
+                    | RRF`,
+            []
+          );
+        });
+
+        test('requires to be preceded by a FORK command', async () => {
+          const { expectErrors } = await setup();
+
+          await expectErrors(`FROM index METADATA _id, _score, _index | RRF`, [
+            '[RRF] Must be immediately preceded by a FORK command.',
+          ]);
+        });
+
+        test('requires to be immediately preceded by a FORK command', async () => {
+          const { expectErrors } = await setup();
+
+          await expectErrors(
+            `FROM index METADATA _id, _score, _index
+                    | FORK
+                      (WHERE keywordField != "" | LIMIT 100)
+                      (SORT doubleField ASC NULLS LAST)
+                    | SORT _id
+                    | RRF`,
+            ['[RRF] Must be immediately preceded by a FORK command.']
+          );
+        });
+
+        test('requires _id, _index and _score metadata to be selected in the FROM command', async () => {
+          const { expectErrors } = await setup();
+
+          await expectErrors(
+            `FROM index
+                    | FORK
+                      (WHERE keywordField != "" | LIMIT 100)
+                      (SORT doubleField ASC NULLS LAST)
+                    | RRF`,
+            [
+              '[RRF] The FROM command is missing the _id METADATA field.',
+              '[RRF] The FROM command is missing the _index METADATA field.',
+              '[RRF] The FROM command is missing the _score METADATA field.',
+            ]
+          );
+        });
+      });
+    });
+  });
+};
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/__tests__/validation.command.rrf.test.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/__tests__/validation.command.rrf.test.ts
new file mode 100644
index 0000000000000..ba0352c8989c5
--- /dev/null
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/__tests__/validation.command.rrf.test.ts
@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import * as helpers from './helpers';
+import { validationRrfCommandTestSuite } from './test_suites/validation.command.rrf';
+
+validationRrfCommandTestSuite(helpers.setup);
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/commands/rrf/index.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/commands/rrf/index.ts
new file mode 100644
index 0000000000000..7290348180918
--- /dev/null
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/commands/rrf/index.ts
@@ -0,0 +1,70 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { ESQLAst, ESQLCommand, ESQLMessage } from '@kbn/esql-ast';
+import { i18n } from '@kbn/i18n';
+import { ReferenceMaps } from '../../types';
+
+export function validate(
+  command: ESQLCommand<'rrf'>,
+  references: ReferenceMaps,
+  ast: ESQLAst
+): ESQLMessage[] {
+  const messages: ESQLMessage[] = [];
+
+  if (!isRrfImmediatelyAfterFork(ast)) {
+    messages.push({
+      location: command.location,
+      text: i18n.translate(
+        'kbn-esql-validation-autocomplete.esql.validation.rrfMissingScoreMetadata',
+        {
+          defaultMessage: '[RRF] Must be immediately preceded by a FORK command.',
+        }
+      ),
+      type: 'error',
+      code: 'rrfNotImmediatelyAfterFork',
+    });
+  }
+
+  if (!references.fields.get('_id')) {
+    messages.push(buildMissingMetadataMessage(command, '_id'));
+  }
+
+  if (!references.fields.get('_index')) {
+    messages.push(buildMissingMetadataMessage(command, '_index'));
+  }
+
+  if (!references.fields.get('_score')) {
+    messages.push(buildMissingMetadataMessage(command, '_score'));
+  }
+
+  return messages;
+}
+
+function buildMissingMetadataMessage(
+  command: ESQLCommand<'rrf'>,
+  metadataField: string
+): ESQLMessage {
+  return {
+    location: command.location,
+    text: i18n.translate('kbn-esql-validation-autocomplete.esql.validation.rrfMissingMetadata', {
+      defaultMessage: `[RRF] The FROM command is missing the {metadataField} METADATA field.`,
+      values: { metadataField },
+    }),
+    type: 'error',
+    code: `rrfMissingMetadata`,
+  };
+}
+
+function isRrfImmediatelyAfterFork(ast: ESQLAst): boolean {
+  const forkIndex = ast.findIndex((cmd) => cmd.name === 'fork');
+  const rrfIndex = ast.findIndex((cmd) => cmd.name === 'rrf');
+
+  return forkIndex !== -1 && rrfIndex === forkIndex + 1;
+}
diff --git a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/validation.ts b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/validation.ts
index 2f267e8002126..24e8d0c8e77bb 100644
--- a/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/validation.ts
+++ b/src/platform/packages/shared/kbn-esql-validation-autocomplete/src/validation/validation.ts
@@ -216,7 +216,7 @@ function validateCommand(
   }
 
   if (commandDef.validate) {
-    messages.push(...commandDef.validate(command, references));
+    messages.push(...commandDef.validate(command, references, ast));
   }
 
   switch (commandDef.name) {