formal-agent-contracts vs JSON Contracts
formal-agent-contracts is a plugin bundle for AI coding tools published by kotaroyamame. Marketplaces we read that list it: 1 (Claude Code: claude-plugins-community). JSON Contracts is an MCP server published by json-contracts. Marketplaces we read that list it: 1 (Official MCP Registry). As of our marketplace pass on 2026-10-24. This pair was picked by a reader, not by our comparison rule, so search engines are asked not to index the page.
Where each is published
| Marketplace |  formal-agent-contracts |  JSON Contracts |
|---|---|---|
| Claude Code: claude-plugins-community | Listed Version: 2.2.0 Forks (GitHub): 0 Stars (GitHub): 1 Not marked · First seen |
Not listed |
| Official MCP Registry | Not listed | Listed Version: 0.1.2 Downloads/month (npm): 211 Downloads/week (npm): 19 Forks (GitHub): 0 Stars (GitHub): 1 Not marked · First seen |
Each figure is the marketplace's own and is never added up across marketplaces. A marketplace that publishes no figure shows none: no number is not zero.
The facts side by side
| Fact | formal-agent-contracts | JSON Contracts |
|---|---|---|
| Marketplaces that list it | 1 | 1 |
| Stars (GitHub) | 1 | 1 |
| Forks (GitHub) | 0 | 0 |
| Last release | Not published | Not published |
| Where it runs (differs) | Installs as a plugin bundle | On your machine (json-contracts) |
| Transport (differs) | Not stated | stdio |
| Tools it declares | Not published | Not published |
| Environment variables it asks for (differs) | Not published | 1, secrets among them: 0 |
| Parts of the bundle (differs) | 15 | Not a bundle |
| Licence (differs) | MIT | Not stated |
| Repository (differs) | github.com/kotaroyamame/formal-agent-contracts | github.com/json-contracts/json-contracts |
| Changes in the last 7 days | 0 | 0 |
| First seen | 2026-10-11 | 2026-10-11 |
Lines where the two differ have a tinted background and bold values. Where the data itself says which value is better (more marketplaces, a larger figure of the same marketplace, a fresher release, a verified mark on a marketplace that lists both), the better one is also marked green with ▲ and the worse one red with ▼. Where it runs, the transport, the tools, the settings, hooks, the bundle's parts, the licence and the week's changes are marked only as different: more or fewer is not better in itself.
What each says it does
formal-agent-contracts
Formal methods toolkit for multi-agent development. Define inter-agent contracts in VDM-SL, verify with VDMJ, prove with Z3, and generate TypeScript/Python code with runtime contract enforcement — all through natural language conversation with Claude.
JSON Contracts
JSON contract registry and validator for structured LLM and agent outputs.
How to run each
formal-agent-contracts As a Claude Code plugin
/plugin marketplace add anthropics/claude-plugins-community
/plugin install formal-agent-contracts@claude-communityJSON Contracts As a local MCP server: npm package
claude mcp add --transport stdio json-contracts -- npx -y json-contractsCommands built only from what the marketplaces declare; the full set for every client is on each card.
Tools each declares
Neither one's marketplaces publish a list of tools, so there is nothing to compare.
Settings each asks for
The marketplaces of formal-agent-contracts publish no settings it asks for, so we do not compare settings.
What it can do: formal-agent-contracts · What it can do: JSON Contracts · Compare two other plugins
Data comes from the public marketplace file https://github.com/anthropics/claude-plugins-community/blob/HEAD/.claude-plugin/marketplace.json. Data comes from the Official MCP Registry (registry.modelcontextprotocol.io), CC0 1.0. Figures come from our own regular passes over the marketplaces, last read on . We publish no contact details for plugin publishers.