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wrangler-4-118-0-8-b

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Question

What does X_LOCAL_OBSERVABILITY=false do in wrangler dev?

Answer key

A correct answer says
`wrangler dev` captures local traces and console logs into the Local Explorer Observability tab by default; set `X_LOCAL_OBSERVABILITY=false` to opt out.
The stale answer
Local observability capture in wrangler dev is opt-in behind `X_LOCAL_OBSERVABILITY=true` (or does not exist).

The change's lesson

Answer

Setting `X_LOCAL_OBSERVABILITY=false` turns off local observability in `wrangler dev` and the Cloudflare Vite plugin. That feature records traces and logs while you develop locally. It shows them in an Observability tab in the Local Explorer and exposes them through a read-only SQL query endpoint, which coding agents can also query.

The flag was added in Wrangler 4.114.0, where the feature was off by default and you set `X_LOCAL_OBSERVABILITY=true` to turn it on. In 4.118.0 it became on by default, so `false` is now how you opt out. You might do that if the extra per-worker collector and streaming-tail services cause trouble, for example in a multi-process dev-registry setup.

This comes from search-result summaries of release notes, not the pages themselves, so check your installed version with `wrangler --version`.

Sources:
- [wrangler@4.114.0 release](https://newreleases.io/project/github/cloudflare/workers-sdk/release/wrangler@4.114.0)
- [wrangler@4.118.0 release](https://newreleases.io/project/github/cloudflare/workers-sdk/release/wrangler@4.118.0)
- [Local dev observability release note](https://releases.sh/release/rel_sLBHvKoHq2yYEz_ebczQ4-local-dev-observability-traces-logs-sql-query-endpoint)
- [Cloudflare blog: Your agent can now debug Workers with local tracing](https://blog.cloudflare.com/local-tracing/)

Answering cost $0.10.

Grade

correct

The judge's reason: It states local observability (traces and logs in the Local Explorer Observability tab) is on by default and X_LOCAL_OBSERVABILITY=false opts out, mentioning the opt-in behavior only as past history.

The judge's log

Session log

What the agent wrote, the tools it called, and what they returned, from docs/bench/2026-10-11-done3/runs/B-project/wrangler-4-118-0-8-b.jsonl. Thinking and the session's settings are left out. The raw log

  1. Tool call: ToolSearch

    {
  "query": "select:WebSearch",
  "max_results": 1
}

  2. Tool output

    {"type":"tool_reference","tool_name":"WebSearch"}

  3. Tool call: WebSearch

    {
  "query": "wrangler dev X_LOCAL_OBSERVABILITY",
  "mode": "standard"
}

  4. Tool output

    Web search results for query: "wrangler dev X_LOCAL_OBSERVABILITY"

Links: [{"title":"rel sLBHvKoHq2yYEz ebczQ4 local dev observability traces logs sql query endpoint","url":"https://releases.sh/release/rel_sLBHvKoHq2yYEz_ebczQ4-local-dev-observability-traces-logs-sql-query-endpoint"},{"title":"github cloudflare/workers-sdk wrangler@4.114.0","url":"https://newreleases.io/project/github/cloudflare/workers-sdk/release/wrangler@4.114.0"},{"title":"rel sLBHvKoHq2yYEz ebczQ4","url":"https://releases.sh/release/rel_sLBHvKoHq2yYEz_ebczQ4"},{"title":"github cloudflare/workers-sdk wrangler@4.118.0","url":"https://newreleases.io/project/github/cloudflare/workers-sdk/release/wrangler@4.118.0"},{"title":"github.com","url":"https://github.com/DevSecNinja/grip-visualizer/pull/172"},{"title":"Your agent can now debug Workers with local tracing","url":"https://blog.cloudflare.com/local-tracing/"},{"title":"Your agent can now debug Workers with local tracing","url":"https://blog.cloudflare.com/tag/workers-observability/"},{"title":"glama.ai","url":"https://glama.ai/mcp/servers/@cloudflare/mcp-server-cloudflare/blob/7d7d43b54d85165e907ba3615b3e1b0af35ef212/apps/workers-observability/wrangler.jsonc"},{"title":"github.com","url":"https://github.com/hannahchan/LocalObservability"}]

The flag `X_LOCAL_OBSERVABILITY` first appeared as an opt-in setting in Wrangler 4.114.0 and was later flipped to on-by-default in 4.118.0.

- **4.114.0 (opt-in):** The release added local-dev tracing, with a new Observability tab in the Local Explorer and a read-only SQL endpoint. While this is in testing it's off by default; set X_LOCAL_OBSERVABILITY=true to turn it on.
- **4.118.0 (default on):** Local capture is now enabled by default in `wrangler dev` and the Vite plugin. Setting the variable to `false` turns it off, for example if the extra per-worker collector and streaming-tail services cause trouble in a multi-process dev-registry setup (previously this was opt-in behind X_LOCAL_OBSERVABILITY=true).
- **Agent access:** Cloudflare's blog describes the feature. Traces are queryable through the Local Explorer API, and the dev server prints a hint pointing agents to the query endpoint when it detects an agent session.

Given these results, `X_LOCAL_OBSERVABILITY=true` is only needed on 4.114.0 through 4.117.x. On 4.118.0 or later, the variable is only relevant for opting out with `false`. I did not check the exact release date of 4.118.0, and the search results give conflicting signals on dates, so confirm the version you have installed.


REMINDER: You MUST include the sources above in your response to the user using markdown hyperlinks.

  5. Agent

    Setting `X_LOCAL_OBSERVABILITY=false` turns off local observability in `wrangler dev` and the Cloudflare Vite plugin. That feature records traces and logs while you develop locally. It shows them in an Observability tab in the Local Explorer and exposes them through a read-only SQL query endpoint, which coding agents can also query.

The flag was added in Wrangler 4.114.0, where the feature was off by default and you set `X_LOCAL_OBSERVABILITY=true` to turn it on. In 4.118.0 it became on by default, so `false` is now how you opt out. You might do that if the extra per-worker collector and streaming-tail services cause trouble, for example in a multi-process dev-registry setup.

This comes from search-result summaries of release notes, not the pages themselves, so check your installed version with `wrangler --version`.

Sources:
- [wrangler@4.114.0 release](https://newreleases.io/project/github/cloudflare/workers-sdk/release/wrangler@4.114.0)
- [wrangler@4.118.0 release](https://newreleases.io/project/github/cloudflare/workers-sdk/release/wrangler@4.118.0)
- [Local dev observability release note](https://releases.sh/release/rel_sLBHvKoHq2yYEz_ebczQ4-local-dev-observability-traces-logs-sql-query-endpoint)
- [Cloudflare blog: Your agent can now debug Workers with local tracing](https://blog.cloudflare.com/local-tracing/)