Why does the plain npm install pick an old version?

npm resolves the unspecified request as the semver range 'agent-browser@*' and excludes candidates whose engines.node requirement isn't met. On Node below 24, 0.27.0 — which has no engines field — is selected instead of 0.41.2, with no error or warning.

What Node version does agent-browser 0.41.2 require?

Its engines field requires node '>=24.0.0' and pnpm '>=11.0.0'. Installing it with '@latest' on an older Node still succeeds but prints an EBADENGINE warning.

Did the author measure the claimed 90% token reduction?

On a local test page, snapshot output was 785 characters versus 1,526 raw characters — about 48.6% reduction. The author notes this differs from the official premise of a Playwright MCP comparison, so it is only a reference value.

Large Language ModelsAI Coding AssistantsZenn AI/ML21h agoNov 8, 2026, 06:00 JST

agent-browser install silently lands on 0.27.0, not 0.41.2

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3 Key Points

What happened
Running plain 'npm install agent-browser' on Node below 24 silently installed version 0.27.0, not the latest 0.41.2, because npm filters out engine-mismatched candidates.
Why it matters
The author confirmed the gap by switching between Node 22 and Node 24 — the same command picked 0.41.2 on Node 24 — so on Node 22 the old version arrives with no error or warning.

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Context & Analysis

The story is less about agent-browser's accessibility-tree approach than about a quiet packaging quirk. Because npm's version-unspecified install is handled as a '*' range resolution, npm first drops any candidate that fails the current Node's engines.node check, then picks among what remains. Version 0.27.0 has no engines field at all, so it survives that filter on Node 22 and gets installed — no error, no warning. The author verified this both ways: on Node v22.23.4 the plain command yielded 0.27.0, and after switching to Node v24.22.2 the same command yielded 0.41.2.

Separately, the author's hands-on run of agent-browser itself went smoothly: open, snapshot, fill, click, and read all worked on a local Japanese test page, with each element carrying a @ref ID like @e1 and no coordinates or pixels involved. The token-saving claim was only partially reproduced — roughly 48.6% fewer characters on a small local page, a different premise from the official Playwright MCP comparison. The sister tool agent-desktop advanced further: accessibility permission was granted under WSLg, but list-apps, list-windows, and launch --activate all failed with ACTION_NOT_SUPPORTED because the WM was Weston, not the GNOME environment the tool's own Linux skill documentation lists as verified.

FAQ

Why does the plain npm install pick an old version?: npm resolves the unspecified request as the semver range 'agent-browser@*' and excludes candidates whose engines.node requirement isn't met. On Node below 24, 0.27.0 — which has no engines field — is selected instead of 0.41.2, with no error or warning.
What Node version does agent-browser 0.41.2 require?: Its engines field requires node '>=24.0.0' and pnpm '>=11.0.0'. Installing it with '@latest' on an older Node still succeeds but prints an EBADENGINE warning.
Did the author measure the claimed 90% token reduction?: On a local test page, snapshot output was 785 characters versus 1,526 raw characters — about 48.6% reduction. The author notes this differs from the official premise of a Playwright MCP comparison, so it is only a reference value.

Zenn AI/MLRead Original Article

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