Debug Tauri DevTools

Use CrabNebula DevTools for the part of a Tauri app that browser DevTools cannot see: Rust-side logs, IPC spans, resolved runtime config, capability state, plugin wiring, and bundled asset resolution.

Trigger

Activate when the user reports or the agent observes any of these:

• a Tauri invoke() call fails, hangs, is unexpectedly slow, or returns wrong data
• a Rust panic/error exists but the failing module or span is unclear
• a plugin, capability, or window-scope permission appears broken
• an asset loads in dev but not in build, or exists locally but not in the bundle
• behavior differs across desktop/mobile or debug/build modes
• you are about to add println!(), guess at serde/config issues, or inspect the browser Network tab for Tauri IPC
• CrabNebula DevTools needs to be installed, configured, or is not connecting

When NOT to use this skill

Do not activate for:

• DOM, CSS, layout, browser-only JavaScript, or framework component debugging
• HTTP/fetch/WebSocket debugging that lives in the browser network stack
• static code review without a live runtime symptom
• cases where the problem is already proven and you only need to implement a fix

Use browser DevTools for webview problems. Use CrabNebula DevTools when the unknown lives behind the webview.

First-time setup

If DevTools is not installed in the project, complete installation before entering the debugging workflow:

1. Check: search src-tauri/Cargo.toml for tauri-plugin-devtools. If absent, or if lib.rs does not register the plugin with .plugin(tauri_plugin_devtools::init()), DevTools is not installed.
2. Install: follow the steps in references/setup/installation-and-config.md. Use the "Which Pattern to Use" table to pick the right initialization pattern for your project.
3. Restart: stop the running app and restart with cargo tauri dev. First run after adding DevTools triggers a longer compilation — wait for the WebSocket URL to appear in terminal output.
4. Verify: confirm DevTools connects — Console tab should show initialization logs, Config → Plugins should list registered plugins, and invoking any #[tauri::command] should produce an entry in the Calls tab.
5. Continue: after verification, proceed to Phase 2 below.

Note: Tauri IPC commands (#[tauri::command]) are automatically instrumented by Tauri core. They appear in the Calls tab without any additional code.

Rust-side visibility map

All "Open first" instructions below require DevTools to be connected. If DevTools is not running, complete the First-time setup section above.

⚠️ Steering: The visibility map assumes DevTools is connected and showing data. If DevTools shows a blank dashboard or no data, this is ITSELF the problem to solve — go to references/setup/installation-and-config.md, not Phase 2.

Use the minimal reading sets at the bottom of this file to load the right references for each symptom category.

Workflow

Follow this order. Do not skip from symptom straight to code edits.

Phase 1 — Establish the failing path

⚠️ Steering: Do NOT skip the DevTools detection check. In derailment testing, agents jumped straight to debugging without DevTools installed, wasting an entire diagnosis cycle. Always verify tauri-plugin-devtools in Cargo.toml first.

• Name the exact action that reproduces the issue.
• Note expected vs actual behavior.
• Record environment: cargo tauri dev, debug build, release build, desktop platform, or mobile target.
• DevTools check: search src-tauri/Cargo.toml for tauri-plugin-devtools. If absent, or if lib.rs does not call .plugin(tauri_plugin_devtools::init()), DevTools is not installed. Follow the First-time setup section above, then return here and continue to Phase 2.

Phase 2 — Observe before theorizing

⚠️ Steering: If operating as an AI agent without visual DevTools UI, do NOT claim you "opened the Calls tab." Instead, use terminal output from cargo tauri dev (DevTools subscriber prints to stderr) or ask the user for screenshots. Fabricating visual evidence is a P0 failure.

• Start in the single tab that matches the symptom (see visibility map).
• Capture exact evidence before browsing other surfaces:
  • Console: target path, error text, fields, panic location
  • Calls: command, args, response/error, timing, nesting
  • Config: capabilities, plugin registration, build/bundle/security values
  • Sources: bundled file presence, exact path, case-sensitive mismatches
• Prefer built-in DevTools filters and sorting before changing code or RUST_LOG.

Agent-mode evidence gathering: When operating without a visual DevTools UI (e.g., an AI agent in a terminal), evidence comes from: (1) terminal output from cargo tauri dev — DevTools subscriber prints tracing events to stderr, (2) adding tracing_subscriber::fmt as a secondary output layer for structured logs, (3) asking the user to share DevTools screenshots or tab exports. Use these sources in place of the visual tab instructions above.

Shortcut for capability/permission errors: If the symptom is clearly a permission error and capability files are accessible, you may inspect src-tauri/capabilities/*.json directly to identify missing permission identifiers. Cross-reference with the error message and references/plugins/capabilities-and-permissions.md. If the fix is unambiguous (a specific permission string is missing), proceed directly to Phase 5. Use DevTools for verification in Phase 6 if available.

Phase 3 — Form 1–3 falsifiable hypotheses

⚠️ Steering: Every hypothesis MUST map to a Phase 4 routing entry. In testing, agents formed hypotheses about sequential processing but had no routing to investigate it — the diagnosis stalled. If your hypothesis does not match a routing entry, you likely need references/performance/profiling-and-optimization.md.

Each hypothesis must identify:

1. the suspected failure mode
2. the exact evidence that would confirm it (from DevTools or static inspection)
3. the next inspection surface or reference (refer to the Phase 4 routing list below)

Good hypothesis shapes:

• "JS arguments do not match the Rust Deserialize struct."
• "The command is blocked on uninstrumented file I/O or lock contention."
• "The plugin is registered, but the capability or window scope is missing."
• "The asset exists in source control but is absent from the bundle."
• "Mobile uses a platform-specific path or permission assumption that desktop does not."
• "Items are processed sequentially — duration scales linearly with input count."
• "The Tauri ACL permission identifier is missing vs an OS-level permission error."

Phase 4 — Inspect the hypothesis path

⚠️ Steering: Before adding #[tracing::instrument], verify that tracing = "0.1" is in Cargo.toml [dependencies]. Missing this dependency causes a compile error that agents misdiagnosed as a Tauri issue.

Before inspecting, review the Decision Rules section below — it contains key conditional routing for common evidence patterns.

Use the narrowest inspection path that can confirm or reject the hypothesis:

• Rust handler / serde / async / state issue → Calls + references/rust/backend-debugging.md
• Need deeper span detail → references/devtools-ipc-span-anatomy.md
• Permission / capability / plugin init issue → Config + Console + references/plugins/capabilities-and-permissions.md
• Sequential/parallel processing or O(n) scaling → Calls + references/performance/profiling-and-optimization.md
• Log visibility or missing dependency logs → references/rust/logging-and-tracing.md
• Subscriber / tauri-plugin-log / custom integration question → references/devtools-integration-patterns.md
• Asset / bundle / build-mode mismatch → Sources + Config + references/devtools-common-debugging-scenarios.md
• Mobile-only divergence → references/mobile/android-ios-debugging.md
• Performance bottleneck or profiling needed → references/performance/profiling-and-optimization.md
• Need tool internals or pipeline limits → references/devtools-architecture-deep-dive.md

If evidence is still incomplete, add visibility instead of guessing. See Guardrails for what NOT to do when adding instrumentation.

• Ensure tracing = "0.1" is in [dependencies] in Cargo.toml. For async instrumentation with .instrument(), also add use tracing::Instrument;.
• For slow/missing spans: add #[tracing::instrument] to internal Rust functions. If the slow code is inline (not in a separate function), use manual spans: let _span = tracing::info_span!("process_item", item = %item).entered(); around the slow section.
• For panics: enable RUST_BACKTRACE=1.
• For missing dependency logs: use the split()/attach_logger() pattern (see references/devtools-integration-patterns.md).
• For dev/build or desktop/mobile differences: compare the same repro in both environments before changing code.

Phase 5 — Separate diagnosis from repair

⚠️ Steering: A "narrow fix" means targeting the confirmed bottleneck — e.g., parallelizing a loop proven slow by span evidence. Do NOT interpret "avoid refactors" as "never change code structure." The guardrail prevents speculative changes, not evidence-based structural fixes.

Only edit app code/config after one hypothesis is confirmed by evidence. See Guardrails on keeping diagnosis and repair separate.

When you do change something:

• Fix the narrow failing path, not nearby speculative code. A "narrow fix" targets the confirmed bottleneck — for example, parallelizing a sequential loop proven slow. This is not a "refactor" in the guardrail sense. A "refactor" would be restructuring unrelated code, renaming modules, or adding abstractions not required by the fix.
• For the fix approach, consult the reference file that matches the confirmed diagnosis — e.g., references/performance/profiling-and-optimization.md for performance issues, references/plugins/capabilities-and-permissions.md for permission issues.
• Keep temporary tracing in place until the verification pass.
• Avoid cleanup refactors until the bug is proven fixed.

Phase 6 — Verify in the same surface

⚠️ Steering: You MUST restart cargo tauri dev after code changes. Agents frequently forgot this step and verified against stale runtime state, declaring bugs "fixed" when the old binary was still running.

Rebuild the app (e.g., restart cargo tauri dev), reconnect DevTools, and reproduce the same user action or invoke call. Confirm the evidence changed where it originally failed:

• Calls: status, response, duration, or child span structure is now correct. Compare duration against the classification table in references/devtools-tab-reference.md — "correct" means the symptom is resolved and the absolute duration falls in an acceptable range for the use case.
• Console: error/panic is gone or replaced by the expected trace sequence
• Config: missing capability/plugin/config value is now present in resolved config
• Sources: missing asset/path mismatch is resolved at runtime
• Mobile/build comparisons: previously divergent evidence now matches the expected platform behavior

Remove DEBUG-ONLY temporary instrumentation (e.g., extra tracing::debug!() events added solely for this diagnosis). KEEP structural instrumentation (#[tracing::instrument] on meaningful functions) for ongoing visibility.

Decision rules

• If DevTools is not installed in the project, install it before any debugging. All other decision rules require DevTools to be running.
• If one child span dominates the total duration, optimize that child first.
• If the parent span is slow but child spans are missing or too small, instrument internal Rust code before refactoring.
• If the Calls response already shows a permission error (or the browser console shows an invoke() rejection), inspect resolved capabilities and window scope before touching the command handler.
• If no IPC call appears at all, check whether the frontend actually invoked the command, whether the command name is wrong, whether a capability blocked it, or whether DevTools was initialized too late.
• If Console is noisy, use UI filters first; only narrow RUST_LOG when throughput is too high to reason about.
• If release builds have no DevTools data, treat that as expected #[cfg(debug_assertions)] behavior and reproduce with a debug-capable target before drawing conclusions.
• If desktop and mobile differ, compare Console and Calls evidence on both platforms before sharing a fix.
• If the error message contains "not allowed" or "capability", this is a Tauri ACL error. If it contains "os error 13" or "Permission denied", this is an OS-level error. These require completely different fixes — do not confuse them.
• If you cannot visually inspect DevTools (e.g., you are an AI agent), use cargo tauri dev terminal output as your primary evidence source. The DevTools subscriber prints tracing events to stderr.

Common agent mistakes

Guardrails

• Do not use Browser Network tools as proof for Tauri IPC behavior.
• Do not change serde structs, capability files, plugin order, or asset paths without first reading the runtime evidence that points there.
• Do not use println!() as your primary Rust debugging surface; use tracing so the data stays in DevTools.
• Do not instrument every function. Add spans only where evidence is missing.
• Do not convert a diagnosis task into a broad refactor.
• Do not claim a root cause until you can point to a concrete log, span, config value, permission, or asset path and point to the exact evidence.

Do this, not that

Recovery paths

• DevTools will not connect or shows no data → references/setup/installation-and-config.md
• tauri-plugin-log conflicts or dependency logs are missing → references/rust/logging-and-tracing.md, references/devtools-integration-patterns.md
• The command is slow or hung but the waterfall is too shallow → references/devtools-ipc-span-anatomy.md, references/rust/backend-debugging.md
• Known symptom, unclear next move → references/devtools-common-debugging-scenarios.md
• Need field-by-field help with tabs, filters, or exports → references/devtools-tab-reference.md
• Need performance or overhead guidance beyond one command → references/performance/profiling-and-optimization.md
• Need to understand pipeline limitations or internal behavior → references/devtools-architecture-deep-dive.md
• Permission/capability error without DevTools → Inspect src-tauri/capabilities/*.json directly. Compare with references/plugins/capabilities-and-permissions.md Common Plugin Permission Identifiers table. Add the missing permission identifier and restart the app.

Minimal reading sets

First-time installation

• references/setup/installation-and-config.md
• If your project uses tauri-plugin-log, also read references/devtools-integration-patterns.md

DevTools setup or connectivity is the problem

• references/setup/installation-and-config.md
• references/rust/logging-and-tracing.md
• references/devtools-integration-patterns.md

An IPC command fails, hangs, returns wrong data, or is slow

• references/devtools-ipc-span-anatomy.md
• references/devtools-common-debugging-scenarios.md
• references/rust/backend-debugging.md
• references/performance/profiling-and-optimization.md

I need better Rust-side visibility

• references/rust/logging-and-tracing.md
• references/rust/backend-debugging.md
• references/devtools-tab-reference.md

A plugin, capability, or resolved config looks wrong

• references/plugins/capabilities-and-permissions.md
• references/devtools-tab-reference.md
• references/devtools-common-debugging-scenarios.md

Permission error on a specific command (quick path)

• references/plugins/capabilities-and-permissions.md — may be the only file needed

It works in dev/desktop but breaks in build/mobile or assets are missing

• references/devtools-common-debugging-scenarios.md
• references/mobile/android-ios-debugging.md
• references/setup/installation-and-config.md
• references/devtools-tab-reference.md

I need subscriber, performance, or internal pipeline details

• references/devtools-integration-patterns.md
• references/performance/profiling-and-optimization.md
• references/devtools-architecture-deep-dive.md

Reference routing

Final reminder

Use CrabNebula DevTools to collect runtime truth, not to justify a hunch. Stay in observation-first mode until you can name the failing command, log target, config value, permission, or asset path and point to the exact evidence.