Eclipse Theia 1.73 Release: News and Noteworthy

We are happy to announce the Eclipse Theia 1.73 release! The release contains in total 68 merged pull requests. In this article, we will highlight some selected improvements and provide an overview of the latest news around Theia.

For those new to Eclipse Theia, it is the next-generation platform for building IDEs and tools for the web or desktop, based on modern state-of-the-art web technologies. With Theia AI, part of the Theia platform, you can also build AI-powered tools and IDEs with ease. For more details about Eclipse Theia, please refer to this article and visit the Theia website.

The Theia project also releases a product, the Theia IDE. The Eclipse Theia IDE is a modern, AI-native, and open IDE for cloud and desktop environments, aimed at end users. The Theia IDE is based on the Theia platform and also includes advanced AI powered features. For more details, see the Theia IDE website.

If you are looking for a simple way to check out the new release, please download and install the Theia IDE, which is based on Theia 1.73.

Eclipse Theia 1.73: Selected features and improvements

In the following, we will highlight some selected improvements in the new release. As usual, we cannot mention all 68 improvements, however we will focus on the most notable changes as well as changes visible to end users. The corresponding pull requests are linked under the respective heading when applicable.

Install MCP Servers and Skills From the AI Registry

AI agents increasingly rely on external building blocks: MCP servers for connecting to APIs, and skills for packaging reusable agent behaviour. So far, finding and installing these has been a bit of a wild west. You had to track down a server, copy its configuration into your settings by hand, and hope it was the right one from a source you trust. Theia 1.73 adds support for the Eclipse Foundation AI Registry, which makes this straightforward.

The AI Registry is a vendor-neutral trust registry for AI artifacts, hosted by the Eclipse Foundation alongside Open VSX. The registry consolidates which organizations have reviewed and endorsed a given artifact, together with ready-to-use, tool-specific install configurations. In other words, it tells you which servers and skills have been vetted, by whom, and how to install them in your tool. The registry is currently in preview and will be extended with more artifact types soon.

In Theia, MCP servers and skills now appear as first-class entries in the Extensions view, right next to Open VSX extensions. Search for one, and install it with a single click. There is no manual configuration to copy and no guesswork about where it came from. A type filter next to the search box lets you narrow results to Extensions, MCP Servers, or Skills.

The registry also keeps installed entries up-to-date. If a newer version is published, the entry offers to Update; if you (or an agent) changed the local configuration, it offers to restore it; and entries that are no longer listed are flagged so you can clean them up. This works the same way for MCP servers and skills, so you always know whether what you have installed still matches what the registry vetted.

Besides browsing from within the IDE, you can also install directly from the AI Registry website: an install link (e.g. theia://install-mcp?id=<serverId>) opens Theia, reveals the matching entry, and shows the install dialog. For MCP servers that need credentials, the dialog prompts for them, including the OAuth Client ID and Secret for servers like Asana (#17703).

For adopters: the integration ships as a new @theia/ai-registry package and is opt-in per product. Enable it by including the package and pointing the configuration at the registry you want to consume. The skills support landed in #17635.

Provider-Native Server-Side Tools

When an AI agents uses tools, the typically run locally inside of the Theia client. With 1.73, agents can also make use of tools that the AI provider runs on its own servers. The model simply calls these tools directly, and Theia shows you what it did and what came back, without anything having to execute on your machine.

The first examples are fetching web pages and running web searches, offered by the providers themselves:

• Anthropic: web_fetch, web_search
• Gemini: url_context, google_search

The video below shows an agent doing web research through Anthropic’s server-side tools, retrieving and combining information from the web without any local setup.

For common needs like web search or fetching a URL, these built-in server tools can take the place of a dedicated MCP server: there is nothing to install, configure, or keep running, since the provider hosts the tool for you. You enable them in the chat capabilities panel, where each available server tool appears under a “Server Tools” group per provider. Because these tools run on the provider’s infrastructure, they are auto-approved and clearly marked, and your selection is remembered per provider.

Mermaid Diagrams in the AI Chat

Fenced mermaid code blocks in agent responses (and in the user interaction tool) now render as actual diagrams. Diagrams are loaded lazily and themed to match the workbench. A small title bar lets the user collapse a diagram to a thumbnail, toggle between the diagram and its source, and zoom, pan, and resize the diagram box. The rendered SVG is sanitized with DOMPurify and Mermaid runs with securityLevel: 'strict', so scripts, event handlers, and remote resource references are stripped.

The architect, coder, and PR-review agent prompts have been adjusted to suggest Mermaid diagrams for architectural concepts, implementations, and flows, kept small because chat space is limited.

OAuth 2.1 for Remote MCP Servers

Remote MCP servers can now authorize via OAuth 2.1. Theia acts as a public client using PKCE, with dynamic client registration when no static client ID is configured. OAuth is set per server through a new oauth block in the ai-features.mcp.mcpServers preference (enabled, clientId, scopes, authorizationServer, resource).

The flow runs on the backend; the frontend only opens the system browser and supplies the callback URL. Authorization codes arrive via a backend callback endpoint (and a loopback server on Electron), tokens are persisted in a credential store and can be cleared via sign-out, and the MCP configuration view shows each server’s auth status with sign-in/sign-out actions. The first concrete adopters are servers like Asana that require an OAuth-authenticated session.

Note that MCPServerManager.removeServer and addOrUpdateServer are now async, which is a small breaking change for adopters integrating against these APIs.

Waiting-For-Input Indicators in the Chat Overview

Long-running agent sessions often pause for a tool confirmation or for a structured question via the user-interaction tool. Until 1.73, there was no clear cue that a session needed attention. In 1.73, the chat overview marks sessions that are waiting for input with a bell icon, an attention-coloured dot, and a bold title; the tooltip shows a “Waiting for your input” badge, and the indicator takes precedence over the running spinner. Beyond the visual cue, it also ties into the agent notifications: with notifications configured, you are alerted when a session needs your attention and can jump straight back to the chat that is waiting for your input.

VS Code registerTool API

Theia 1.73 implements the VS Code lm.registerTool and lm.invokeTool plugin APIs. Tools registered this way are fully integrated with Theia AI: they can be referenced in user or system prompts via ~{toolId}, are properly auto-completed in the chat input, and the LLM can invoke them through the normal tool-call mechanism.

Custom Agents Reorganized Around .agents

Two PRs reshape how custom agents are stored on disk to match the existing skills convention:

Per-agent folders with frontmatter moves custom agents from a shared customAgents.yml into a dedicated folder per agent, with metadata in YAML frontmatter on top of the prompt body:

<scope>/agents/<agent-id>/
├── agent.md                       # frontmatter metadata + prompt body
├── prompt.prompttemplate          # default-variant customization
└── <variant>.prompttemplate       # additional prompt variants

Existing customAgents.yml files (and sibling <agent-name>_prompt*.prompttemplate files) are migrated on request: a notification on startup offers to migrate, and nothing on disk changes until you click Migrate, which writes the per-agent folders and keeps the original yml as customAgents.yml.bak. You can dismiss it with Don't Show Again, and the AI: Re-run custom-agent migration command triggers it manually at any time. The folder name is the agent id, so it is the single source of truth.

.agents as the default workspace folder then aligns custom agents with skills, which already live in .agents/skills. Custom agents are now discovered from both .agents/agents/ and .prompts/agents/ of each workspace root and new agents are created under .agents/agents/<id>/agent.md by default. .prompts/agents/ keeps being discovered for backward compatibility.

Other Theia AI Improvements

• Tool confirmation shortcuts and batch allow: Ctrl+Enter allows and Ctrl+Shift+Backspace denies the latest pending tool confirmation, and the Tools tab gains an “Allow Default Tools” action that bulk-approves built-in tools while leaving MCP and confirm defaults untouched.
• Faster AI workspace file tools: findFilesByPattern, getWorkspaceDirectoryStructure, and getWorkspaceFileList now run on the backend instead of issuing one RPC per directory, so full-tree queries on large or remote workspaces return in tens of milliseconds instead of minutes.
• PR Review walkthrough: The PR review agent now guides the reviewer through the change instead of just listing issues, with a renamed “Highlights & Findings” section and an optional “Why it matters” line per area.

VS Code Compatibility

• VS Code API 1.125.0: VS Code API compatibility has been upgraded to 1.125.0, unblocking extensions that target this version. There were no public vscode.d.ts changes since 1.121.1.
• @theia/preview deprecated: The legacy @theia/preview package is deprecated and no longer published to npm; Markdown preview is fully covered by the built-in vscode.markdown-language-features plugin. The package code will be removed in a future release (~3 months).

File Watchers: Bounded by files.watcherExclude

Several PRs (#17598, #17630, #17633, #17609) close long-standing gaps that could exhaust fs.inotify.max_user_watches on Linux even with files.watcherExclude configured. Excludes are now passed to the native watcher so excluded directories are never crawled, applied consistently to all watchers (including plugin and language-server watchers), and out-of-workspace ancestor watches no longer trigger full recursive crawls. Watching is also more robust in esbuild-bundled apps.

Terminal

• Terminal paste on macOS: Pasting into the terminal with Cmd+V (or right-click → Paste) now works on macOS Electron, and the terminal.enablePaste / terminal.enableCopy preferences take effect again.
• Explicit terminal ownership: With terminal.grouping.mode: tree, terminal ownership is now assigned explicitly at creation time, fixing deletion and multi-group display for integrated task terminals.

Editor and Workbench

• Custom editor identifiers align with default editors: Custom editors now embed the file URI in their tab id and align their icons and captions with the default editor, so external tooling can target them.
• Disambiguate duplicate view entries: Following VS Code’s pattern, views and view containers that share a label (e.g. the three “Claude Code” containers) now show their location in the View menu and View: Open View, so they are no longer indistinguishable.
• Physical-keystroke capture for keybindings: The Keyboard Shortcuts edit dialog now captures real keystrokes instead of requiring you to type the key combination as a string.

Platform

• React 19 peer support: @theia/core now accepts React 18 or 19 as a peer dependency, so adopters can move to React 19 ahead of Theia switching its own baseline to React 19 around August or September 2026.
• Wildcard support for logger configuration: Per-logger levels in the log configuration file now support glob-style wildcards (e.g. "ai-core*": "error").
• DebugSession injectable: DebugSession can now be replaced via DI. The factory’s get(...) method is renamed to createSession(...), which is a breaking change for adopters that extended the factory directly.

Additional Improvements

The 1.73 release also includes several less visible but valuable changes:

• Hardened WebSocket and HTTP transport validation: Same-origin checks, engine.io transport-level validation, and a SameSite cookie-based connection token now gate both HTTP API and WebSocket access. Contributed on behalf of STMicroelectronics.
• VSXRegistry service moved to the backend: The Open VSX client now runs entirely on the backend and exposes a higher-level API to the frontend, with the frontend Request Service restricted to a per-extension allow-list. Contributed on behalf of STMicroelectronics.
• console → ILogger migration: Raw console calls have been replaced with the unified DI ILogger across feature packages.

For a complete overview of all changes in this release, please refer to the 1.73 milestone. All these features and improvements (in total 68) were the result of one month of intensive development. Eclipse Theia follows a monthly release schedule. We are looking forward to the next release due next month, stay tuned! To be notified about future releases, follow us on LinkedIn or follow Theia on Twitter and subscribe to our mailing list.

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