JSON Contracts
NPM · JSON-CONTRACTS · SCANNED OCT 2
JSON contract registry and validator for structured LLM and agent outputs.
Available components
How this component scores in each security and reliability category. Every signal is checked automatically from public evidence about the published package, including repeated runs of it in an isolated sandbox, and we only credit what we can confirm. How we score → Why this is hard to score →
Supply Chain Security98
- No malware found by supply-chain analysis.Pass
- No known CVEs affecting this package version or its production dependencies.Pass
- No install/post-install scripts declared.Pass
- 31 of 96 dependencies flagged as unhealthy. View diagnostics → Partial
Provenance & Transparency45
- Source repository is publicly reachable at the declared URL. View diagnostics → Pass
- Provenance check failed: no build-provenance attestation is published. See how to fix → View diagnostics → Fail
- Clear OSI-approved license (Apache-2.0).Pass
- Actively maintained (last published 149 days ago).Pass
- Disclosure check failed: no security disclosure policy was found in the source repository. See how to fix → Fail
Schema Quality & AI Usability79
- 100% of prompts and resources have a non-trivial description (not blank, and not just the item's name).Pass
- AI-judged instruction clarity (good).Pass
- Tool/resource definitions use about 258 tokens (~32/item across 8 items; 8 tools + 0 resources), lean.Pass
- Usage-examples check failed: none of the tools include examples. See how to fix → Fail
Stability & Change Management83
- Stability observed for 25 of 30 days with no destabilising changes; credit accrues until the full window elapses.Partial
Tool Coverage71
- 100% of tools have a non-trivial description (not blank, and not just the tool's name).Pass
- 0% of tool parameters carry a description.Fail
- Structured output schemas are declared (100% of tools); any adoption earns full credit.Pass
Tool Safety100
- No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.Pass
- We read all 8 captured tool definition(s), and no name or description among them implies an irreversible operation.Pass
- An AI judge read all 8 captured unit(s) of tool text and found none that tries to manipulate the model reading it.Pass
Capabilities100
- Implements a supported MCP spec version (2025-11-25); the latest is 2026-07-28.Pass
How do I install the JSON Contracts MCP server?
JSON Contracts runs locally as an npm package, launched with npx -y json-contracts. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.
npm · json-contracts
claude mcp add json-contracts-json-contracts -- npx -y json-contracts
{
"mcpServers": {
"json-contracts-json-contracts": {
"command": "npx",
"args": [
"-y",
"json-contracts"
]
}
}
} {
"servers": {
"json-contracts-json-contracts": {
"command": "npx",
"args": [
"-y",
"json-contracts"
]
}
}
} codex mcp add json-contracts-json-contracts -- npx -y json-contracts
{
"$schema": "https://opencode.ai/config.json",
"mcp": {
"json-contracts-json-contracts": {
"type": "local",
"command": [
"npx",
"-y",
"json-contracts"
],
"enabled": true
}
}
} openclaw mcp add json-contracts-json-contracts --command npx --arg -y --arg json-contracts
mcp_servers:
json-contracts-json-contracts:
command: "npx"
args: ["-y", "json-contracts"] {
"McpServers": {
"json-contracts-json-contracts": {
"Transport": "stdio",
"Command": "npx",
"Arguments": [
"-y",
"json-contracts"
]
}
}
} assistant mcp add json-contracts-json-contracts -t stdio -c npx -a -y json-contracts
{
"mcpServers": {
"json-contracts-json-contracts": {
"command": "npx",
"args": [
"-y",
"json-contracts"
]
}
}
} Every change we have recorded for this component, newest first. Security-relevant changes are always shown. ▲ marks a change for the better, ▼ a change for the worse; unmarked changes are neutral.
- 1 Oct 26 −2
- Stability: pass → 0.80 functional
- 30 Sept 26 0
- Stability: 0.97 → pass security
- 29 Sept 26 +1
No change was recorded against any check on this day. Stability & Change Management went from 93 to 97. That category is still filling its 30-day observation window: 28 days of observed history at the previous scan, 29 at this one. The score rises as the window fills, whether or not the server changes.
- 28 Sept 26 0
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 27 Sept 26 +1
No change was recorded against any check on this day. Stability & Change Management went from 87 to 90. That category is still filling its 30-day observation window: 26 days of observed history at the previous scan, 27 at this one. The score rises as the window fills, whether or not the server changes.
- 26 Sept 26 +15
- Malware scan: unverified → pass ▲ security
- 25 Sept 26 0
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 24 Sept 26 −2
- Stability: pass → 0.80 functional
Diagnostic detail from the automated scan of this channel: what the scanner observed at each step, so you can see exactly where a check passed or failed. It is informational only and never changes the trust score.
Captured 2 Oct 2026 · Analysed npm/json-contracts@0.1.2
Provenance No attestation
The registry publishes no build provenance for this version, so there is nothing to verify.
| Result | No attestation |
|---|---|
| Ecosystem | npm |
Background: How many MCP packages publish verified provenance →
Dependencies 96 packages
| Packages resolved | 96 |
|---|---|
| Stale | 31 |
| Tree resolution | Complete |
Background: SBOMs and build attestations, explained →
The tools this component advertises to a client, with an estimated token cost for each. Expand a tool to see its parameters and schema. The per-tool counts are indicative and are not scored directly; the schema's total context footprint is one signal in Schema Quality & AI Usability. A tool's description is untrusted text the model reads on every call, which is what makes this list a security surface and not just an inventory: how tool poisoning works →
get_edit_contract ~58
Return schema, rules, current JSON, edit instructions, and input so the agent/model can edit existing JSON.
| Name | Type | Req | Description |
|---|---|---|---|
| context | object | – | – |
| contract | string | yes | – |
| currentJson | – | yes | – |
| input | string | yes | – |
| Name | Type | Req | Description |
|---|---|---|---|
| context | object | yes | – |
| contract | string | yes | – |
| contractHash | string | yes | – |
| currentJson | – | yes | – |
| description | string | yes | – |
| examples | array | yes | – |
| input | string | yes | – |
| instructions | array | yes | – |
| operation | – | yes | – |
| operationExamples | array | yes | – |
| operationRules | array | yes | – |
| rules | array | yes | – |
| schema | object | yes | – |
| schemaHash | string | yes | – |
No examples provided.
get_json_contract ~49
Return schema, rules, examples, instructions, and input so the agent/model can produce JSON.
| Name | Type | Req | Description |
|---|---|---|---|
| context | object | – | – |
| contract | string | yes | – |
| input | string | yes | – |
| Name | Type | Req | Description |
|---|---|---|---|
| context | object | yes | – |
| contract | string | yes | – |
| contractHash | string | yes | – |
| description | string | yes | – |
| examples | array | yes | – |
| input | string | yes | – |
| instructions | array | yes | – |
| operation | – | yes | – |
| operationExamples | array | yes | – |
| operationRules | array | yes | – |
| rules | array | yes | – |
| schema | object | yes | – |
| schemaHash | string | yes | – |
No examples provided.
get_repair_contract ~47
Return schema, rules, previous invalid JSON, validation errors, and repair instructions.
| Name | Type | Req | Description |
|---|---|---|---|
| contract | string | yes | – |
| invalidJson | – | yes | – |
| validationErrors | array | – | – |
| Name | Type | Req | Description |
|---|---|---|---|
| contract | string | yes | – |
| contractHash | string | yes | – |
| examples | array | yes | – |
| instructions | array | yes | – |
| invalidJson | – | yes | – |
| rules | array | yes | – |
| schema | object | yes | – |
| schemaHash | string | yes | – |
| validationErrors | array | yes | – |
No examples provided.
list_contracts ~15
List currently loaded JSON contracts.
Input schema present but exposes no named parameters.
| Name | Type | Req | Description |
|---|---|---|---|
| contracts | array | yes | – |
No examples provided.
read_contract ~21
Read a loaded JSON contract.
| Name | Type | Req | Description |
|---|---|---|---|
| contract | string | yes | – |
| Name | Type | Req | Description |
|---|---|---|---|
| contract | string | yes | – |
| contractHash | string | yes | – |
| description | string | yes | – |
| examples | array | yes | – |
| operations | object | yes | – |
| rules | array | yes | – |
| schema | object | yes | – |
| schemaHash | string | yes | – |
No examples provided.
reload_contracts ~20
Rescan the JSON contracts directory and reload valid contracts.
Input schema present but exposes no named parameters.
| Name | Type | Req | Description |
|---|---|---|---|
| contracts | array | yes | – |
| loaded | number | yes | – |
No examples provided.
status ~19
Return json-contracts MCP server status and loaded contract metadata.
Input schema present but exposes no named parameters.
| Name | Type | Req | Description |
|---|---|---|---|
| allowInvalidContracts | boolean | yes | – |
| contracts | array | yes | – |
| contractsDir | string | yes | – |
| loaded | number | yes | – |
| server | – | yes | – |
| version | string | yes | – |
| watchContracts | boolean | yes | – |
No examples provided.
validate_json ~29
Validate agent-produced JSON against a contract schema.
| Name | Type | Req | Description |
|---|---|---|---|
| contract | string | yes | – |
| json | – | yes | – |
| Name | Type | Req | Description |
|---|---|---|---|
| contract | string | yes | – |
| errors | array | yes | – |
| json | – | – | – |
| valid | boolean | yes | – |
No examples provided.
What is the JSON Contracts MCP server?
JSON Contracts is an MCP server listed in the public MCP registry as io.github.json-contracts/json-contracts. JSON contract registry and validator for structured LLM and agent outputs. This page covers its npm package (json-contracts).
Is the JSON Contracts MCP server safe to use?
JSON Contracts scores 80 out of 100 on VerifyMCP. We found no known CVEs affecting it as of 2 October 2026. It declares no install or post-install scripts. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.
What tools does the JSON Contracts MCP server expose?
JSON Contracts exposes 8 tools: list_contracts, read_contract, get_json_contract, get_edit_contract, validate_json, and 3 more. Their descriptions and schemas cost roughly 258 tokens of context every time the server is loaded.
Is the JSON Contracts MCP server still maintained?
JSON Contracts is still listed as active in the MCP registry. We last reached this channel on 2 October 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.
What licence is the JSON Contracts MCP server under?
JSON Contracts declares the Apache-2.0 licence, which is OSI-approved. That covers the source only, and says nothing about the cost of any service it calls.