Toolkit Labsjsonshim-mcp — JSON recovery over MCP
A one-file MCP stdio server that gives an agent two tools, recover_json and
classify_json_failure, for the case where a model was asked for JSON and returned something
else. Standard library only, no install, no network call, CC0 1.0.
Install
Download jsonshim_mcp.py, put it
anywhere, and point your MCP client at it with an absolute path:
{"mcpServers":{"jsonshim":{"command":"python3","args":["/absolute/path/jsonshim_mcp.py"]}}}What it scores — and where it loses
Measured on the same 300 cases as the leaderboard: 218 of 300 exact, 193 of 275 recoverable, 0 of the 25 unrecoverable cases invented, and 55 false refusals. Read the last two together: it never fabricates a value, and it pays for that by refusing 55 recoverable documents it could have salvaged.
It is weaker than json-repair, which recovers 264 of the same 275, and it is
not the same code as jsonshim, which scores 282 of 300 on the full corpus. If you want
the strongest recovery, this is not it.
| category | recovered |
|---|---|
brackets | 5 / 25 |
comments | 25 / 25 |
fenced | 25 / 25 |
prose_wrapped | 25 / 25 |
py_literals | 21 / 25 |
raw_control | 0 / 25 |
single_quotes | 25 / 25 |
trailing_comma | 25 / 25 |
truncated | 0 / 25 |
unquoted_keys | 25 / 25 |
unrecoverable | 25 / 25 |
wrappers | 17 / 25 |
Its two blind spots are flat zeros and are not being hidden: truncated output 0 of 25 and raw control characters 0 of 25, with brackets at 5 of 25. A reply cut off mid-object and a reply carrying a literal newline inside a string both come back refused, every time.
Files here
| file | bytes |
|---|---|
LICENSE | 467 |
jsonshim_mcp.py | 8 807 |
The corpus it was scored on
300 labelled cases, 30 free as a stratified sample. The tool is free either way.
Single developer — €29 · Team / CI licence — €99
Instant download after payment; digital goods, delivered immediately. Payments processed by Stripe. Prices include VAT where applicable.