Error adding marketplace on Ubuntu and Claude Code

[vneyman]

What happen
run below:
claude plugin marketplace add JuliusBrussee/caveman && claude plugin install caveman@caveman

Expected
Install marketplace

Before/after example

Adding marketplace…
✘ Failed to add marketplace: Failed to load marketplace configuration: JSON Parse error: Unrecognized token '<'

Platform

• [x ] Claude Code
• Codex
• Other: ___

Version / install method
claude version 2.1.112

[jeancarlosleonvega]

similar issue on ubuntu 24

Failed to install plugin "caveman@caveman": Plugin "caveman" not found in marketplace "caveman"

[AmirF194]

Investigated this while triaging open issues here. Reproduced two related failures for claude plugin marketplace add JuliusBrussee/caveman in clean node:20-slim Docker containers with no git and no SSH configured:

• Claude Code v2.1.112 (pinned in this report), no git binary on PATH: fails with spawn git ENOENT from git -c core.sshCommand=ssh ... clone ... git@github.com:JuliusBrussee/caveman.git ...
• Claude Code v2.1.197 (current), git installed but no SSH key/agent configured: the SSH clone attempt fails with ERR_STREAM_PREMATURE_CLOSE. Running git config --global url."https://github.com/".insteadOf "git@github.com:" first makes the CLI print "SSH not configured, cloning via HTTPS", and the install then succeeds.

.claude-plugin/marketplace.json was already valid JSON at the commit that was current when this issue was filed (checked with git show <pre-2026-04-16 commit>:.claude-plugin/marketplace.json), so the file itself does not look like the problem.

I could not reproduce the exact JSON Parse error: Unrecognized token '<' from the original report. The marketplace-add flow appears to have changed since v2.1.112: it now does a full git clone of the repo rather than fetching JSON directly, so whatever produced that error text may no longer be reachable on the current CLI. Both failures I did reproduce point at the same thing: claude plugin marketplace add depends on a working git binary plus SSH access to GitHub, and it does not fall back to HTTPS on its own in either environment above.

This looks like Claude Code CLI behavior rather than anything in this repo's marketplace.json. If it is worth a line in INSTALL.md for users hitting install failures, the git config --global url.insteadOf command above is the workaround that got it working here.