<p><em>All tests run on an 8-year-old MacBook Air.</em></p> <p>Android Studio's logcat is fine. But opening a full IDE just to read logs and debug an error felt like overkill.</p> <p>I built a lightweight logcat viewer in Rust + Tauri. Then I added a Gemini button next to every error line. One click — AI diagnosis, no copy-pasting, no context switching.</p> <p>Here's how the AI integration works.</p> <h2> The idea: click the error, get the diagnosis </h2> <p>Every error line in the viewer has a small button. Click it, and the app:</p> <ol> <li>Pulls that error line plus the surrounding 50–100 lines from a ring buffer</li> <li>Strips any PII (IP addresses, emails) before sending</li> <li>Sends the context to Gemini with a carefully crafted prompt</li> <li>Displays the diagnosis in an overlay panel</li> </ol> <p>No manual copy-pasting. No switching to a browser. The diagnosis appears where the error is.</p> <h2> The ring buffer design </h2> <p>Logcat streams thousands of lines per minute. You can't keep all of them in memory.</p> <p>The Rust backend maintains a ring buffer of the last 2,000 lines. When the user clicks diagnose, slicing out the relevant context is instant:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight rust"><code><span class="k">pub</span> <span class="k">struct</span> <span class="n">LogRingBuffer</span> <span class="p">{</span> <span class="n">lines</span><span class="p">:</span> <span class="n">VecDeque</span><span class="p">,</span> <span class="n">capacity</span><span class="p">:</span> <span class="nb">usize</span><span class="p">,</span> <span class="p">}</span> <span class="k">impl</span> <span class="n">LogRingBuffer</span> <span class="p">{</span> <span class="k">pub</span> <span class="k">fn</span> <span class="nf">push</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span> <span class="k">self</span><span class="p">,</span> <span class="n">line</span><span class="p">:</span> <span class="n">LogLine</span><span class="p">)</span> <span class="p">{</span> <span class="k">if</span> <span class="k">self</span><span class="py">.lines</span><span class="nf">.len</span><span class="p">()</span> <span class="o">&gt;=</span> <span class="k">self</span><span class="py">.capacity</span> <span class="p">{</span> <span class="k">self</span><span class="py">.lines</span><span class="nf">.pop_front</span><span class="p">();</span> <span class="p">}</span> <span class="k">self</span><span class="py">.lines</span><span class="nf">.push_back</span><span class="p">(</span><span class="n">line</span><span class="p">);</span> <span class="p">}</span> <span class="k">pub</span> <span class="k">fn</span> <span class="nf">context_around</span><span class="p">(</span><span class="o">&amp;</span><span class="k">self</span><span class="p">,</span> <span class="n">target_idx</span><span class="p">:</span> <span class="nb">usize</span><span class="p">,</span> <span class="n">window</span><span class="p">:</span> <span class="nb">usize</span><span class="p">)</span> <span class="k">-&gt;</span> <span class="nb">Vec</span><span class="o">&lt;&amp;</span><span class="n">LogLine</span><span class="o">&gt;</span> <span class="p">{</span> <span class="k">let</span> <span class="n">start</span> <span class="o">=</span> <span class="n">target_idx</span><span class="nf">.saturating_sub</span><span class="p">(</span><span class="n">window</span><span class="p">);</span> <span class="k">let</span> <span class="n">end</span> <span class="o">=</span> <span class="p">(</span><span class="n">target_idx</span> <span class="o">+</span> <span class="n">window</span><span class="p">)</span><span class="nf">.min</span><span class="p">(</span><span class="k">self</span><span class="py">.lines</span><span class="nf">.len</span><span class="p">());</span> <span class="k">self</span><span class="py">.lines</span><span class="nf">.range</span><span class="p">(</span><span class="n">start</span><span class="o">..</span><span class="n">end</span><span class="p">)</span><span class="nf">.collect</span><span class="p">()</span> <span class="p">}</span> <span class="p">}</span> </code></pre> </div> <p>2,000 lines, instant slice, minimal memory.</p> <h2> The prompt </h2> <div class="highlight js-code-highlight"> <pre class="highlight rust"><code><span class="k">let</span> <span class="n">system</span> <span class="o">=</span> <span class="s">"You are an Android development specialist. </span><span class="err">\</span><span class="s"> Analyze the following logcat output and explain </span><span class="err">\</span><span class="s"> the root cause and fix concisely."</span><span class="p">;</span> <span class="k">let</span> <span class="n">context_text</span> <span class="o">=</span> <span class="n">context_lines</span> <span class="nf">.iter</span><span class="p">()</span> <span class="nf">.map</span><span class="p">(|</span><span class="n">l</span><span class="p">|</span> <span class="n">l</span><span class="py">.raw</span><span class="nf">.as_str</span><span class="p">())</span> <span class="py">.collect</span><span class="p">::</span><span class="o">&gt;</span><span class="p">()</span> <span class="nf">.join</span><span class="p">(</span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="k">let</span> <span class="n">prompt</span> <span class="o">=</span> <span class="nd">format!</span><span class="p">(</span><span class="s">"{}</span><span class="se">\n\n</span><span class="s">Logcat:</span><span class="se">\n</span><span class="s">{}"</span><span class="p">,</span> <span class="n">system</span><span class="p">,</span> <span class="n">context_text</span><span class="p">);</span> </code></pre> </div> <p>Simple. The context does the heavy lifting — Gemini doesn't need elaborate prompting when the relevant lines are right there.</p> <h2> Result </h2> <p>Open the viewer, run the app, see an error → click the button → diagnosis in 2–3 seconds. No IDE required.</p> <p>HiyokoLogcat is free and open source → github.com/hiyoyok/HiyokoLogcat<br> X → <a class="mentioned-user" href="https://dev.to/hiyoyok">@hiyoyok</a></p>