Fixing ElevenLabs Android Client Tool Response Issues

Hey there, fellow developers! If you're diving into the exciting world of voice agents on Android using the amazing ElevenLabs SDK, you might just hit a rather peculiar roadblock, especially when dealing with client tools that are supposed to send results back to the LLM. We're talking about that sneaky expects_response: true setting. This isn't just a minor glitch; it's a significant hurdle that can stop your interactive voice agent dead in its tracks. In this deep dive, we're going to unravel the mystery behind why client tools with expects_response: true don't seem to work, why the server doesn't send the expects_response field, and why trying to send results manually often leads to rejection. Get ready to arm yourselves with knowledge, because we're about to tackle this ElevenLabs Android SDK challenge head-on!

Building dynamic, responsive voice agents is all about smooth communication between your app and the large language model. When your Android app, powered by the ElevenLabs SDK, makes a client_tool_call, it often needs to perform some action—like fetching data or interacting with a device feature—and then report the outcome back to the AI. This is precisely where expects_response: true comes into play. It's designed to tell the ElevenLabs backend, "Hey, expect some data back from my client tool after this call!" However, what many of us are finding, after hours of debugging, is that this crucial flag seems to be getting lost in translation. The server, for some reason, isn't including the expects_response field in the WebSocket event it sends to your Android application. This oversight has a domino effect: without that explicit true flag, the SDK mistakenly assumes false, and consequently, it never attempts to send the tool's result back to the LLM. Think of it like a mailman waiting for a package delivery confirmation slip that never arrives; he simply moves on, even if there's a package waiting to be sent! This isn't just an inconvenience; it effectively renders any client tool requiring a return value unusable, fundamentally breaking the interactive loop crucial for sophisticated voice agents. We'll explore this core issue, showing you exactly where the breakdown happens, from the configured REST API settings to the actual WebSocket payloads received by your app, and discuss why this silence from the server is causing such a fuss for ElevenLabs Android developers.

The Core Problem: expects_response Field Missing in ElevenLabs Android SDK

Alright, guys, let's get right to the heart of the matter: the expects_response field missing from the WebSocket events in the ElevenLabs Android SDK. This is the core issue that's causing so much head-scratching for developers trying to build sophisticated voice agents. When you configure a client tool via the ElevenLabs REST API, you specify expects_response: true because your tool, after doing its thing (like fetching information or performing an action), needs to return data back to the large language model (LLM) for it to continue the conversation intelligently. It's a fundamental part of creating truly interactive experiences, allowing the AI to adapt its responses based on real-world outcomes reported by your app.

However, what many of us are discovering, after meticulously debugging our ElevenLabs Android applications, is that despite setting expects_response: true in the tool's configuration through the API, the actual WebSocket event that your app receives for a client_tool_call does not include this field at all. You can verify your tool configuration all day long with a curl command, seeing "expects_response": true and "response_timeout_secs": 5 staring back at you, confirming your setup is correct on the server side. But when that client_tool_call event hits your Android device, it's conspicuously absent. The SDK's event parser, as we'll see, is built to expect this field, and if it's not there, it defaults to false. This default interpretation is critical because it tells the SDK, "Nope, no need to send a response back for this one!"—even when you explicitly told the API that a response is expected. This isn't just a minor oversight; it fundamentally breaks the two-way communication required for dynamic ElevenLabs voice agents.

The implications of this missing field are profound. If your voice agent asks, "What's the weather like in Paris?" and your tool is supposed to fetch that data and send it back, the LLM will never receive the result. It's like talking to a brick wall! The SDK's parsing logic, specifically in ConversationEventParser.kt, checks for expectsResponse = obj.get("expects_response")?.asBoolean == true. If obj.get("expects_response") returns null because the field isn't present, then asBoolean is never called, and the == true comparison naturally evaluates to false. This effectively turns all your expects_response: true tools into fire-and-forget tools, which only work for actions that don't need to inform the LLM of their outcome. For anything requiring feedback—which is, let's be honest, most useful voice agent interactions—this bug makes the system unusable. This issue highlights a crucial disconnect between the tool configuration and the real-time event delivery mechanism, leaving ElevenLabs Android developers in a tough spot where their sophisticated tool designs are being undermined by a missing flag.

The Frustrating Workaround Attempt: Manual sendToolResult() and Policy Violations

So, you've figured out the expects_response field is missing from the WebSocket event, and the ElevenLabs Android SDK isn't sending results automatically. What's the natural developer instinct? "I'll just send it manually, then!" This is where many of us, myself included, turn to the onUnhandledClientToolCall callback provided by the SDK. It seems like a perfectly logical escape hatch, right? The idea is, if the SDK isn't going to handle sending the response because it thinks expects_response is false, we'll just step in and explicitly call session?.sendToolResult() ourselves. We get the toolCallId, prepare our result map (usually with success, result data, and potentially error fields), and then confidently invoke sendToolResult() with that ID and our carefully crafted payload. It feels like we're outsmarting the system, ensuring our ElevenLabs voice agent gets the data it needs.

But here's where the frustration truly kicks in, and it's a real head-scratcher. The moment you try to send that tool result manually after the server failed to include expects_response: true in its initial client_tool_call event, the server immediately slams the door in your face! You'll be greeted with a rather cryptic, yet firm, error message: {"type": "error", "message": "received 1008 (policy violation) Invalid message received"}. Talk about a buzzkill! This isn't just a generic network error; it's a specific WebSocket status code, 1008 (Policy Violation), which indicates that the endpoint (the ElevenLabs server, in this case) has terminated the connection because it received a message that violates its policy. In simple terms, the server is saying, "What you just sent? Nope, that's not allowed right now!" This leaves ElevenLabs Android developers completely stuck: the SDK won't send results because it thinks expects_response is false, and when you try to send them manually, the server actively rejects them.

This policy violation points to a deeper issue. It suggests that the ElevenLabs server, having omitted expects_response: true from the client_tool_call event, isn't actually expecting a tool result for that specific call at all. So, when your manual sendToolResult() comes in, it's like trying to return an item to a store that never sold it to you in the first place—they're just not set up to receive it. It highlights a critical discrepancy: the API configuration says "expect a response," but the real-time WebSocket protocol implementation seems to be saying "don't expect one" by its omission. This policy violation effectively makes client tools that require any sort of feedback to the LLM completely unusable. While fire-and-forget tools (those that just perform an action and don't return data) work absolutely fine, anything that needs to send data back to the agent is broken. This creates a massive roadblock for building sophisticated interactive ElevenLabs Android voice agents and highlights the urgent need for a server-side fix to properly send the expects_response field in all relevant client_tool_call events.

Deep Dive into the ElevenLabs Android SDK Code: What's Happening Under the Hood?

Alright, folks, let's roll up our sleeves and get a bit technical. To truly understand why our ElevenLabs Android client tools are hitting this snag, we need to peer into the very code of the ElevenLabs Android SDK. Specifically, two files are key players in this drama: ConversationEventParser.kt and ConversationEventHandler.kt. These are the unsung heroes (or villains, depending on your perspective right now!) that dictate how your app interprets events from the ElevenLabs server and, crucially, when it decides to send tool results back.

In ConversationEventParser.kt, this is where the magic (or lack thereof) happens during the parsing of incoming WebSocket events. When a client_tool_call event arrives, the SDK tries to parse its various fields. The problematic line for us is: expectsResponse = obj.get("expects_response")?.asBoolean == true. Let's break this down. obj represents the JSON object of the event. obj.get("expects_response") attempts to retrieve the JSON element associated with the key "expects_response". Now, here's the kicker: if the server doesn't include the "expects_response" field in the JSON payload at all (which, as we've seen, is exactly what's happening), then obj.get("expects_response") returns null. When you then try to call ?.asBoolean on null, it gracefully (but problematically for us) returns null. And finally, null == true evaluates to false. Voila! Because the field is missing, the expectsResponse property within your ClientToolCall event object is set to false, even though your tool was configured via the API to expect a response. This subtle parsing logic, while perhaps intended for robust error handling for missing fields, becomes a major impediment when the server consistently omits a field that should be present for expects_response: true scenarios in ElevenLabs Android voice agents.

Now, let's switch over to ConversationEventHandler.kt, which is responsible for handling these parsed events and deciding what to do next. This is where the decision to send a tool result or not is made. You'll find a conditional block that looks something like this: if (event.expectsResponse && result != null) { // send result }. See it? The SDK will only attempt to send a tool result if two conditions are met: first, event.expectsResponse must be true, and second, result (your tool's outcome) must not be null. Since our ConversationEventParser.kt has already decided that event.expectsResponse is false (because the field was missing from the server's WebSocket event), the entire if condition fails. The code block to // send result is simply never executed. This means your carefully prepared tool results, no matter how valuable, are simply ignored by the SDK, because it genuinely believes the server isn't expecting them for this particular client_tool_call. This mechanical flow, dictated by the SDK's internal logic, perfectly explains why our interactive ElevenLabs Android client tools are failing to communicate their outcomes. It's not a bug in our tool logic, but rather a fundamental disconnect in the event parsing and handling, all stemming from that initial missing expects_response field from the ElevenLabs server.

Decoding the Error: "1008 (policy violation) Invalid message received"

Okay, guys, let's talk about that dreaded "received 1008 (policy violation) Invalid message received" error. It's a real kick in the gut when you're already struggling with ElevenLabs Android client tool issues and trying to manually send results. This isn't just some random network hiccup; 1008 is a specific WebSocket close code, indicating a policy violation. In the world of WebSockets, this typically means the server has received a message from the client that it deems unacceptable or not conforming to its established rules or state. It's like trying to speak a language the other party isn't expecting, or providing information out of context. For ElevenLabs Android developers, understanding this error is crucial to grasping why our manual workarounds aren't cutting it.

So, what could constitute a policy violation in this context? Let's brainstorm some possibilities and connect them back to our core problem with expects_response: true and the missing field. First, and most likely, if the ElevenLabs server did not send expects_response: true in its client_tool_call event, it effectively signaled to your app, "This is a fire-and-forget tool; don't send me a result." Therefore, when you then proceed to send a sendToolResult() message, the server is caught off guard. It wasn't in a state where it was expecting a tool result for that specific tool_call_id. From its perspective, your message is out of policy because there was no prior instruction to anticipate a response. It's a state mismatch: the server is acting as if no response is needed, while your client is trying to provide one.

Another angle could be the message format itself. While the sendToolResult method in the SDK is designed to create a valid message, perhaps the server has different expectations when it hasn't explicitly requested a response. For instance, maybe it expects a different set of fields, or perhaps the absence of expects_response: true in the initial event subtly changes the expected structure or type of subsequent messages it will accept for that call ID. Less likely, but still a possibility, could be timing issues or even authentication nuances if the manual sendToolResult somehow differs from what the SDK would normally send when expectsResponse is true. However, given that the sendToolResult method is part of the official SDK, it's highly improbable that the format itself is inherently wrong. It's far more probable that the context or state in which the message is sent is the problem.

Ultimately, the 1008 policy violation error powerfully reinforces the core issue: the server needs to explicitly indicate that it's expecting a response. Without that expects_response: true flag in the client_tool_call event, the server simply isn't ready or configured to receive a sendToolResult message, leading to the connection being unceremoniously dropped. This effectively makes client tools with responses unusable for ElevenLabs Android voice agents and underscores that the true fix lies on the server side to correctly emit that crucial field, thus aligning the expectations between the server and the client. Until then, our attempts to manually bridge this communication gap will continue to be rejected, leaving us in this frustrating limbo.

Potential Solutions & What You Can Do (for now, guys!)

Alright, so we've identified the problem, we've seen how the ElevenLabs Android SDK processes it, and we've experienced the frustration of the server rejecting our manual attempts. What can we, as developers, do about these ElevenLabs Android client tool issues? While some solutions require changes from ElevenLabs themselves, there are steps you can take and avenues to explore to keep your voice agent projects moving forward.

First and foremost, the Official Fix is undeniably paramount. The root cause lies with the ElevenLabs server not consistently including the expects_response field in the WebSocket client_tool_call events when a tool is configured with expects_response: true via the API. This isn't something we can fix client-side without potentially breaking things or creating unstable workarounds. ElevenLabs needs to ensure their server-side implementation correctly emits this flag in the WebSocket events. This is the cleanest, most robust, and ultimately necessary solution for all ElevenLabs Android developers to build truly interactive and reliable voice agents. Don't let anyone tell you otherwise; this is where the core fix needs to happen.

In the interim, you might consider a SDK Patch (Temporary/Community). Could the ElevenLabs Android SDK be modified to make an educated guess? For example, if a tool's configuration (queried separately via REST API) explicitly states expects_response: true, could the SDK be patched to assume expectsResponse is true for that tool_call_id, even if the field is missing from the WebSocket event? This is a risky proposition, guys. It might lead to policy violation errors if the server still isn't internally ready to receive the response, or it could introduce subtle bugs. If you go this route, you'd need to fork the SDK, implement the logic, and rigorously test it. It's a heavy lift, and might not even work if the server side isn't synchronized.

Another approach, especially for new tools you're designing, could involve Alternative Tool Design. Can you redesign your tools to be more "fire-and-forget"? This might involve your tool pushing its results to a separate endpoint or database, and then your LLM-based agent polling that endpoint for updates, rather than expecting a direct return via sendToolResult(). This adds significant latency and complexity, making real-time conversational agents less fluid, but it might be a temporary escape hatch if direct responses are absolutely essential. However, for quick, conversational turns, this workaround is far from ideal for an ElevenLabs voice agent.

Could you try a Direct API Call (Complex)? This would involve bypassing the sendToolResult mechanism entirely and instead making a direct REST API call to ElevenLabs to submit the tool result. The challenge here is knowing if such an API endpoint exists, what its format would be, and how to associate it with the specific tool_call_id in a real-time, synchronous manner. This would likely be even more complex than patching the SDK and would almost certainly introduce latency, making it unsuitable for highly responsive voice agents.

The most crucial immediate step, my friends, is Contacting ElevenLabs Support. This is not a bug in your code; it's a platform-level issue. Provide them with detailed logs, including the full WebSocket event your app receives, your API tool configuration, and the exact error message from your manual sendToolResult() attempt. The more specific information you provide, the better. This helps them diagnose and prioritize a fix for all ElevenLabs Android developers. Lastly, engage in Community Discussion! Share your experiences on forums, GitHub issues, or developer communities. The more developers report this consistent behavior, the higher the visibility and likelihood of a swift resolution from ElevenLabs.

Wrapping It Up: Don't Let expects_response Derail Your Voice Agent!

Whew! We've covered a lot of ground, haven't we? It's clear that the current situation with ElevenLabs Android client tools and the expects_response: true flag is a significant challenge for anyone building sophisticated voice agents. The core issue, guys, boils down to the ElevenLabs server not sending that crucial expects_response field in its WebSocket events, leading to the SDK misinterpreting the intent and subsequently, the server rejecting any manual attempts to send results as a "policy violation." It's a frustrating loop that can halt your development in its tracks.

But don't lose hope! Understanding why this is happening is the first step toward finding a resolution. While there isn't a perfect client-side workaround right now, the most powerful thing you can do is clearly articulate this issue to ElevenLabs support and engage with the developer community. Your detailed reports are invaluable for them to identify and implement the necessary server-side fix. Until then, remember that fire-and-forget tools can still be effective, but for truly interactive ElevenLabs Android voice agents that need two-way communication, we'll need that server-side update.

Keep pushing those boundaries, keep building amazing things, and let's collectively advocate for a smooth, reliable experience with the ElevenLabs Android SDK. Your innovative voice agent ideas are worth it, and with the right fix, they'll truly shine!