/tidewave-integration

name: tidewave-integration
description: "Tidewave MCP runtime tools — debugging, smoke testing, live state inspection, SQL queries, hex docs. Use when evaluating code in a running Phoenix app."
effort: low
user-invocable: false

Tidewave MCP Integration

Runtime intelligence for Phoenix apps via MCP. Prefer Tidewave tools over Bash when available.

Iron Laws — Never Violate These

1. **DEV ONLY** — Never use Tidewave tools in production contexts. Avoid on shared dev servers with production data copies 2. **PREFER TIDEWAVE OVER BASH** — `mcp__tidewave__get_docs` > `web_fetch`, `execute_sql_query` > `psql` 3. **CHECK AVAILABILITY FIRST** — Call Tidewave only when matching `mcp__tidewave__*` tools are present 4. **SQL IS READ-HEAVY** — Use `execute_sql_query` for SELECT, be careful with mutations 5. **EXACT VERSIONS** — `get_docs` returns docs for YOUR mix.lock versions, not latest

Quick Reference

| Task | Tidewave Tool | Fallback | |------|---------------|----------| | Get docs | `mcp__tidewave__get_docs Module.func/3` | `web_fetch hexdocs.pm/...` | | Run code | `mcp__tidewave__project_eval` | `mix run -e "code"` | | SQL query | `mcp__tidewave__execute_sql_query` | `psql $DATABASE_URL` | | Find source | `mcp__tidewave__get_source_location` | `grep -rn "defmodule"` | | Inspect DOM | `mcp__Tidewave-Web__browser_eval` | Manual browser inspection | | List schemas | `mcp__tidewave__get_ecto_schemas` | Read `lib/*/schemas/` | | Read logs | `mcp__tidewave__get_logs level: :error` | `tail -f log/dev.log` |

Detection

# Check endpoint
curl -s http://localhost:4000/tidewave/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"ping"}'

Or use `/mcp` in Claude Code to see connected servers.

Essential Patterns

Test Function Immediately

# mcp__tidewave__project_eval
MyApp.Accounts.create_user(%{email: "test@example.com"})

Verify Migration

-- mcp__tidewave__execute_sql_query
SELECT column_name, data_type FROM information_schema.columns
WHERE table_name = 'users';

Debug LiveView (with PID from browser)

# mcp__tidewave__project_eval
pid = pid("0.1234.0")
:sys.get_state(pid) |> Map.get(:socket) |> Map.get(:assigns) |> Map.keys()

Setup Requirements

# mix.exs
{:tidewave, "~> 0.6", only: :dev}

# endpoint.ex (in dev block)
plug Tidewave

# config/dev.exs (for LiveView source mapping)
config :phoenix_live_view,
  debug_heex_annotations: true,
  debug_attributes: true

The dependency and endpoint plug expose Tidewave's streamable HTTP server; they do not register it with an MCP client. Configure the current runtime separately with `http://localhost:<port>/tidewave/mcp`, then verify that Tidewave tools are available before relying on this skill.

Reliability Guards

**Worktree/port check (FIRST, in multi-worktree setups)**: multiple worktrees = multiple dev servers on different ports. Before trusting any Tidewave result, confirm the endpoint belongs to THIS checkout: grep `config/dev.exs` for the configured port, and verify with `project_eval File.cwd!()` — if it returns a different worktree path, you're debugging the wrong server.

**Schema introspection BEFORE SQL**: never guess column names. Run `get_ecto_schemas` (or query `information_schema.columns`) before writing SQL against a table you haven't already introspected this session. A guessed-column error costs more than the introspection.

**Output-size guard**: runtime output is unbounded. Always cap it — `LIMIT 20` in SQL, `Enum.take(20)` in evals, `inspect(x, limit: 50, printable_limit: 500)` for large structs. Re-query narrower rather than dumping wide.

**browser_eval fallback**: if `mcp__Tidewave-Web__browser_eval` is absent or errors, don't stall — inspect the same state server-side: LiveView assigns via `:sys.get_state(pid)` in `project_eval`, rendered HTML via `Phoenix.LiveViewTest`, or read the template source directly.

**QA walkthrough pattern**: after a feature completes, run a short checklist through `project_eval`/`browser_eval`: create the record, fetch it back, exercise the main event, check `get_logs level: :error` is clean. Report each step's pass/fail — not just "smoke test passed".

Proactive Runtime Checks

Don't just use Tidewave reactively. **Query runtime state at workflow checkpoints** automatically:

• **After code edits**: `get_logs level: :error` (catch runtime crashes)
• **After features complete**: `project_eval` smoke test (behavioral check)
• **Before planning**: `get_ecto_schemas` + routes eval (concrete context)
• **When investigating**: Auto-capture errors before asking user
• **LiveView UI bugs**: `browser_eval` to inspect DOM state before editing components

See `${CLAUDE_SKILL_DIR}/references/proactive-patterns.md` for full integration points.

References

For detailed patterns, see:

• `${CLAUDE_SKILL_DIR}/references/proactive-patterns.md` - Push-like runtime patterns at workflow checkpoints
• `${CLAUDE_SKILL_DIR}/references/tool-examples.md` - Complete tool usage examples
• `${CLAUDE_SKILL_DIR}/references/validation-checklist.md` - Runtime validation patterns