diff --git a/extensions/studio/src/browser/c-language/c-declaration-service.ts b/extensions/studio/src/browser/c-language/c-declaration-service.ts
new file mode 100644
--- /dev/null
+++ b/extensions/studio/src/browser/c-language/c-declaration-service.ts
@@ -0,0 +1,168 @@
+// SPDX-FileCopyrightText: 2026 Star Haven contributors
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import { injectable, inject } from "@theia/core/shared/inversify";
+import { FileService } from "@theia/filesystem/lib/browser/file-service";
+import URI from "@theia/core/lib/common/uri";
+import type { ILanguageFeaturesService } from "@theia/monaco-editor-core/esm/vs/editor/common/services/languageFeatures";
+import type { CancellationToken } from "@theia/monaco-editor-core/esm/vs/editor/editor.api";
+import type { ITextModel } from "@theia/monaco-editor-core/esm/vs/editor/common/model";
+
+export interface DeclarationInfo {
+  fileLines: string[];
+  lineIndex: number;
+  docLines?: string[];
+  declLine: string;
+}
+
+export function parseDocComment(
+  fileLines: string[],
+  declarationLineIndex: number,
+): string[] | undefined {
+  const lines: string[] = [];
+  for (let i = declarationLineIndex - 1; i >= 0; i--) {
+    const trimmed = fileLines[i].trimStart();
+    if (trimmed.startsWith("///")) {
+      const content = trimmed.startsWith("/// ")
+        ? trimmed.slice(4)
+        : trimmed.slice(3);
+      lines.unshift(content);
+    } else {
+      break;
+    }
+  }
+  return lines.length > 0 ? lines : undefined;
+}
+
+export function parseEvtParams(docLines: string[]): string[] {
+  const params: string[] = [];
+  for (const line of docLines) {
+    const match = line.match(/^@param\s+(\w+)/);
+    if (match) {
+      params.push(match[1]);
+    }
+  }
+  return params;
+}
+
+export interface EvtOutput {
+  name: string;
+  description: string;
+}
+
+export function parseEvtOutputs(docLines: string[]): EvtOutput[] {
+  const outputs: EvtOutput[] = [];
+  for (const line of docLines) {
+    const match = line.match(/^@evtout\s+(\w+)\s+(.*)/);
+    if (match) {
+      outputs.push({ name: match[1], description: match[2] });
+    }
+  }
+  return outputs;
+}
+
+export function stripEvtTags(docLines: string[]): string[] {
+  return docLines.filter(
+    (line) =>
+      !line.startsWith("@param") &&
+      !line.startsWith("@evtout") &&
+      !line.startsWith("@evtapi"),
+  );
+}
+
+@injectable()
+export class CDeclarationService {
+  @inject(FileService)
+  protected readonly fileService!: FileService;
+
+  // Cache file contents by URI
+  protected readonly fileCache = new Map<string, string>();
+
+  /** Find declaration/definition locations for a symbol, checking declaration first. */
+  async findLocations(
+    featuresService: ILanguageFeaturesService,
+    model: ITextModel,
+    position: { lineNumber: number; column: number },
+    token: CancellationToken,
+  ): Promise<{ uri: string; line: number }[]> {
+    const locations: { uri: string; line: number }[] = [];
+    const seen = new Set<string>();
+
+    for (const registry of [
+      featuresService.declarationProvider,
+      featuresService.definitionProvider,
+    ]) {
+      for (const provider of registry.ordered(model)) {
+        if (token.isCancellationRequested) {
+          return locations;
+        }
+        const method =
+          "provideDeclaration" in provider
+            ? (provider as any).provideDeclaration
+            : (provider as any).provideDefinition;
+        const result = await method.call(provider, model, position, token);
+        if (!result) {
+          continue;
+        }
+        const items = Array.isArray(result) ? result : [result];
+        for (const item of items) {
+          if (!item?.uri || item.range == null) {
+            continue;
+          }
+          const line: number =
+            item.range.startLineNumber ?? item.range.start?.line + 1;
+          if (!line) {
+            continue;
+          }
+          const key = `${item.uri.toString()}:${line}`;
+          if (!seen.has(key)) {
+            seen.add(key);
+            locations.push({ uri: item.uri.toString(), line });
+          }
+        }
+        break;
+      }
+    }
+
+    return locations;
+  }
+
+  /** Read a file and return declaration info at the given location. */
+  async getDeclarationInfo(
+    uri: string,
+    line: number,
+  ): Promise<DeclarationInfo | null> {
+    const fileLines = await this.readFileLines(uri);
+    if (!fileLines) {
+      return null;
+    }
+
+    const lineIndex = line - 1;
+    if (lineIndex < 0 || lineIndex >= fileLines.length) {
+      return null;
+    }
+
+    return {
+      fileLines,
+      lineIndex,
+      docLines: parseDocComment(fileLines, lineIndex),
+      declLine: fileLines[lineIndex],
+    };
+  }
+
+  protected async readFileLines(uri: string): Promise<string[] | null> {
+    const cached = this.fileCache.get(uri);
+    if (cached !== undefined) {
+      return cached.split("\n");
+    }
+
+    try {
+      const fileContent = await this.fileService.read(new URI(uri));
+      this.fileCache.set(uri, fileContent.value);
+      return fileContent.value.split("\n");
+    } catch {
+      return null;
+    }
+  }
+}
diff --git a/extensions/studio/src/browser/c-language/doc-comment-hover.ts b/extensions/studio/src/browser/c-language/doc-comment-hover.ts
--- a/extensions/studio/src/browser/c-language/doc-comment-hover.ts
+++ b/extensions/studio/src/browser/c-language/doc-comment-hover.ts
@@ -4,8 +4,6 @@ // SPDX-License-Identifier: AGPL-3.0-or-later
 
 import { injectable, inject } from "@theia/core/shared/inversify";
 import { FrontendApplicationContribution } from "@theia/core/lib/browser";
-import { FileService } from "@theia/filesystem/lib/browser/file-service";
-import URI from "@theia/core/lib/common/uri";
 import { StandaloneServices } from "@theia/monaco-editor-core/esm/vs/editor/standalone/browser/standaloneServices";
 import { ILanguageFeaturesService } from "@theia/monaco-editor-core/esm/vs/editor/common/services/languageFeatures";
 import type {
@@ -13,61 +11,12 @@ Position,
   CancellationToken,
 } from "@theia/monaco-editor-core/esm/vs/editor/editor.api";
 import type { ITextModel } from "@theia/monaco-editor-core/esm/vs/editor/common/model";
-
-interface EvtOutput {
-  name: string;
-  description: string;
-}
-
-function parseDocComment(
-  fileLines: string[],
-  declarationLineIndex: number,
-): string[] | undefined {
-  const lines: string[] = [];
-  for (let i = declarationLineIndex - 1; i >= 0; i--) {
-    const trimmed = fileLines[i].trimStart();
-    if (trimmed.startsWith("///")) {
-      const content = trimmed.startsWith("/// ")
-        ? trimmed.slice(4)
-        : trimmed.slice(3);
-      lines.unshift(content);
-    } else {
-      break;
-    }
-  }
-  return lines.length > 0 ? lines : undefined;
-}
-
-function parseEvtParams(docLines: string[]): string[] {
-  const params: string[] = [];
-  for (const line of docLines) {
-    const match = line.match(/^@param\s+(\w+)/);
-    if (match) {
-      params.push(match[1]);
-    }
-  }
-  return params;
-}
-
-function parseEvtOutputs(docLines: string[]): EvtOutput[] {
-  const outputs: EvtOutput[] = [];
-  for (const line of docLines) {
-    const match = line.match(/^@evtout\s+(\w+)\s+(.*)/);
-    if (match) {
-      outputs.push({ name: match[1], description: match[2] });
-    }
-  }
-  return outputs;
-}
-
-function stripEvtTags(docLines: string[]): string[] {
-  return docLines.filter(
-    (line) =>
-      !line.startsWith("@param") &&
-      !line.startsWith("@evtout") &&
-      !line.startsWith("@evtapi"),
-  );
-}
+import {
+  CDeclarationService,
+  parseEvtParams,
+  parseEvtOutputs,
+  stripEvtTags,
+} from "./c-declaration-service";
 
 function formatHover(signature: string, docLines?: string[]): string {
   const body = docLines?.join("\n").trim();
@@ -79,8 +28,8 @@
 function buildHover(
   fileLines: string[],
   lineIndex: number,
+  docLines?: string[],
 ): string | undefined {
-  const docLines = parseDocComment(fileLines, lineIndex);
   const declLine = fileLines[lineIndex];
 
   const apiCallableMatch = declLine.match(/API_CALLABLE\((\w+)\)/);
@@ -156,8 +105,8 @@ @injectable()
 export class DocCommentHoverContribution
   implements FrontendApplicationContribution
 {
-  @inject(FileService)
-  protected readonly fileService!: FileService;
+  @inject(CDeclarationService)
+  protected readonly declarationService!: CDeclarationService;
 
   onStart(): void {
     const featuresService = StandaloneServices.get(ILanguageFeaturesService);
@@ -237,9 +186,7 @@ model: ITextModel,
     position: Position,
     token: CancellationToken,
   ): Promise<string | null> {
-    // Try declaration first (header files with doc comments),
-    // then fall back to definition
-    const locations = await this.findLocations(
+    const locations = await this.declarationService.findLocations(
       featuresService,
       model,
       position,
@@ -247,84 +194,19 @@ token,
     );
 
     for (const loc of locations) {
-      const hover = await this.buildHoverFromLocation(loc);
+      const info = await this.declarationService.getDeclarationInfo(
+        loc.uri,
+        loc.line,
+      );
+      if (!info) {
+        continue;
+      }
+      const hover = buildHover(info.fileLines, info.lineIndex, info.docLines);
       if (hover) {
         return hover;
       }
     }
 
     return null;
-  }
-
-  protected async findLocations(
-    featuresService: ILanguageFeaturesService,
-    model: ITextModel,
-    position: Position,
-    token: CancellationToken,
-  ): Promise<{ uri: string; line: number }[]> {
-    const locations: { uri: string; line: number }[] = [];
-    const seen = new Set<string>();
-
-    for (const registry of [
-      featuresService.declarationProvider,
-      featuresService.definitionProvider,
-    ]) {
-      for (const provider of registry.ordered(model)) {
-        if (token.isCancellationRequested) {
-          return locations;
-        }
-        const method =
-          "provideDeclaration" in provider
-            ? (provider as any).provideDeclaration
-            : (provider as any).provideDefinition;
-        const result = await method.call(provider, model, position, token);
-        if (!result) {
-          continue;
-        }
-        const items = Array.isArray(result) ? result : [result];
-        for (const item of items) {
-          if (!item?.uri || item.range == null) {
-            continue;
-          }
-          const line: number =
-            item.range.startLineNumber ?? item.range.start?.line + 1;
-          if (!line) {
-            continue;
-          }
-          const key = `${item.uri.toString()}:${line}`;
-          if (!seen.has(key)) {
-            seen.add(key);
-            locations.push({ uri: item.uri.toString(), line });
-          }
-        }
-        break;
-      }
-    }
-
-    return locations;
-  }
-
-  protected async buildHoverFromLocation(loc: {
-    uri: string;
-    line: number;
-  }): Promise<string | null> {
-    const targetUri = new URI(loc.uri);
-
-    let content: string;
-    try {
-      const fileContent = await this.fileService.read(targetUri);
-      content = fileContent.value;
-    } catch {
-      return null;
-    }
-
-    const fileLines = content.split("\n");
-    const lineIndex = loc.line - 1;
-
-    if (lineIndex < 0 || lineIndex >= fileLines.length) {
-      return null;
-    }
-
-    return buildHover(fileLines, lineIndex) ?? null;
   }
 }
diff --git a/extensions/studio/src/browser/c-language/evt-call-inlay-hints.ts b/extensions/studio/src/browser/c-language/evt-call-inlay-hints.ts
new file mode 100644
--- /dev/null
+++ b/extensions/studio/src/browser/c-language/evt-call-inlay-hints.ts
@@ -0,0 +1,228 @@
+// SPDX-FileCopyrightText: 2026 Star Haven contributors
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import { injectable, inject } from "@theia/core/shared/inversify";
+import { FrontendApplicationContribution } from "@theia/core/lib/browser";
+import { Disposable, DisposableCollection } from "@theia/core/lib/common";
+import { StandaloneServices } from "@theia/monaco-editor-core/esm/vs/editor/standalone/browser/standaloneServices";
+import { ILanguageFeaturesService } from "@theia/monaco-editor-core/esm/vs/editor/common/services/languageFeatures";
+import type { CancellationToken } from "@theia/monaco-editor-core/esm/vs/editor/editor.api";
+import type { ITextModel } from "@theia/monaco-editor-core/esm/vs/editor/common/model";
+import { CDeclarationService, parseEvtParams } from "./c-declaration-service";
+
+const CALL_PATTERN = /\bCall\s*\(/g;
+
+/** Parse Call() arguments, handling nested parens like Float(1.0). */
+function parseCallArgs(
+  lineContent: string,
+  callOpenIndex: number,
+): { text: string; startCol: number }[] | undefined {
+  const args: { text: string; startCol: number }[] = [];
+  let depth = 1;
+  let current = "";
+  let startCol = callOpenIndex + 1;
+  let i = callOpenIndex + 1;
+
+  while (i < lineContent.length && depth > 0) {
+    const ch = lineContent[i];
+    if (ch === "(") {
+      depth++;
+      current += ch;
+    } else if (ch === ")") {
+      depth--;
+      if (depth === 0) {
+        if (current.trim()) {
+          args.push({ text: current.trim(), startCol });
+        }
+      } else {
+        current += ch;
+      }
+    } else if (ch === "," && depth === 1) {
+      if (current.trim()) {
+        args.push({ text: current.trim(), startCol });
+      }
+      current = "";
+      startCol = i + 1;
+    } else {
+      if (current.trim() === "" && ch !== " " && ch !== "\t") {
+        startCol = i;
+      }
+      current += ch;
+    }
+    i++;
+  }
+
+  if (depth !== 0) {
+    return undefined;
+  }
+
+  return args.length > 0 ? args : undefined;
+}
+
+@injectable()
+export class EvtCallInlayHintsContribution
+  implements FrontendApplicationContribution
+{
+  @inject(CDeclarationService)
+  protected readonly declarationService!: CDeclarationService;
+
+  protected readonly toDispose = new DisposableCollection();
+
+  // Cache param names per function name
+  protected readonly paramCache = new Map<string, string[] | null>();
+
+  onStart(): void {
+    const featuresService = StandaloneServices.get(ILanguageFeaturesService);
+
+    for (const languageId of ["c", "cpp"]) {
+      const disposable = featuresService.inlayHintsProvider.register(
+        languageId,
+        {
+          provideInlayHints: async (
+            model: ITextModel,
+            range: any,
+            token: CancellationToken,
+          ) => {
+            try {
+              return await this.provideInlayHints(
+                featuresService,
+                model,
+                range,
+                token,
+              );
+            } catch {
+              return { hints: [], dispose() {} };
+            }
+          },
+        },
+      );
+      this.toDispose.push(Disposable.create(() => disposable.dispose()));
+    }
+  }
+
+  onStop(): void {
+    this.toDispose.dispose();
+  }
+
+  protected async provideInlayHints(
+    featuresService: ILanguageFeaturesService,
+    model: ITextModel,
+    range: { startLineNumber: number; endLineNumber: number },
+    token: CancellationToken,
+  ): Promise<{ hints: any[]; dispose(): void }> {
+    const hints: any[] = [];
+
+    for (
+      let lineNumber = range.startLineNumber;
+      lineNumber <= range.endLineNumber;
+      lineNumber++
+    ) {
+      if (token.isCancellationRequested) {
+        break;
+      }
+
+      const lineContent = model.getLineContent(lineNumber);
+      CALL_PATTERN.lastIndex = 0;
+
+      let match;
+      while ((match = CALL_PATTERN.exec(lineContent)) !== null) {
+        const callStart = match.index + match[0].length - 1;
+        const args = parseCallArgs(lineContent, callStart);
+        if (!args || args.length < 2) {
+          continue;
+        }
+
+        const funcName = args[0].text;
+        const paramArgs = args.slice(1);
+
+        const paramNames = await this.getParamNames(
+          featuresService,
+          model,
+          lineNumber,
+          args[0].startCol + 1,
+          funcName,
+          token,
+        );
+
+        if (!paramNames || paramNames.length === 0) {
+          continue;
+        }
+
+        for (let i = 0; i < paramArgs.length && i < paramNames.length; i++) {
+          hints.push({
+            label: `${paramNames[i]}:`,
+            position: {
+              lineNumber,
+              column: paramArgs[i].startCol + 1,
+            },
+            kind: 2, // InlayHintKind.Parameter
+            paddingRight: true,
+          });
+        }
+      }
+    }
+
+    return { hints, dispose() {} };
+  }
+
+  protected async getParamNames(
+    featuresService: ILanguageFeaturesService,
+    model: ITextModel,
+    lineNumber: number,
+    column: number,
+    funcName: string,
+    token: CancellationToken,
+  ): Promise<string[] | null> {
+    const cached = this.paramCache.get(funcName);
+    if (cached !== undefined) {
+      return cached;
+    }
+
+    const params = await this.resolveParamNames(
+      featuresService,
+      model,
+      { lineNumber, column },
+      token,
+    );
+
+    this.paramCache.set(funcName, params);
+    return params;
+  }
+
+  protected async resolveParamNames(
+    featuresService: ILanguageFeaturesService,
+    model: ITextModel,
+    position: { lineNumber: number; column: number },
+    token: CancellationToken,
+  ): Promise<string[] | null> {
+    const locations = await this.declarationService.findLocations(
+      featuresService,
+      model,
+      position,
+      token,
+    );
+
+    for (const loc of locations) {
+      const info = await this.declarationService.getDeclarationInfo(
+        loc.uri,
+        loc.line,
+      );
+      if (!info) {
+        continue;
+      }
+      if (!info.declLine.match(/API_CALLABLE\(/)) {
+        continue;
+      }
+      if (!info.docLines) {
+        continue;
+      }
+      const params = parseEvtParams(info.docLines);
+      if (params.length > 0) {
+        return params;
+      }
+    }
+
+    return null;
+  }
+}
diff --git a/extensions/studio/src/browser/studio-frontend-module.ts b/extensions/studio/src/browser/studio-frontend-module.ts
--- a/extensions/studio/src/browser/studio-frontend-module.ts
+++ b/extensions/studio/src/browser/studio-frontend-module.ts
@@ -22,7 +22,9 @@ AssetBrowserUndoRedoHandler,
 } from "./asset-browser/contribution";
 import { LayoutContribution } from "./layout-contribution";
 import { CommentFontDecorator } from "./comment-font-decorator";
+import { CDeclarationService } from "./c-language/c-declaration-service";
 import { DocCommentHoverContribution } from "./c-language/doc-comment-hover";
+import { EvtCallInlayHintsContribution } from "./c-language/evt-call-inlay-hints";
 
 import "../../src/browser/asset-browser/style.css";
 import "../../src/browser/fonts/fonts.css";
@@ -54,6 +56,13 @@
   bind(CommentFontDecorator).toSelf().inSingletonScope();
   bind(FrontendApplicationContribution).toService(CommentFontDecorator);
 
+  bind(CDeclarationService).toSelf().inSingletonScope();
+
   bind(DocCommentHoverContribution).toSelf().inSingletonScope();
   bind(FrontendApplicationContribution).toService(DocCommentHoverContribution);
+
+  bind(EvtCallInlayHintsContribution).toSelf().inSingletonScope();
+  bind(FrontendApplicationContribution).toService(
+    EvtCallInlayHintsContribution,
+  );
 });