Registries Host, Directories Curate
A registry is where tools live. npm, PyPI, Docker Hub: these are registries. When you publish an MCP server to npm, you're adding it to a registry. The registry hosts the package, handles versioning, and distributes it to anyone who installs it. Registries generally accept any valid package without editorial review.
A directory is where tools are listed and evaluated. Directories like Smithery, Glama, and mcp.so maintain curated lists of MCP servers with descriptions, categories, and sometimes quality assessments. Directories have varying levels of editorial oversight, from fully automated scraping to manual review.
The Quality Signal Difference
Being on a registry tells you almost nothing about quality. Any developer can publish an npm package. The package might be excellent, mediocre, malicious, or an abandoned experiment. The registry doesn't distinguish.
Being on a curated directory carries more weight. Someone (a person or an automated system with quality thresholds) decided the tool was worth listing. The level of confidence this provides depends on the directory's curation standards. A directory with strict editorial review provides a stronger signal than one that auto-imports from registries.
This is why cross-referencing across directories is valuable. A tool that appears in five curated directories has passed five independent evaluations. A tool that only appears in registries hasn't been evaluated by anyone besides its creator.
Why Both Matter
Registries provide completeness. Every published tool is there. Directories provide quality filtering. The tools that pass curation are there. Neither alone gives you what you need: complete coverage with quality signals.
Aggregation platforms like Skillful.sh pull from both. They include tools from registries (so you don't miss niche options) and enrich them with directory presence data, security scores, and maintenance metrics. This gives you the breadth of a registry with the quality signals of directories.
Related Reading
- The Directory Problem: Too Many Sources, Not Enough Signal
- How Skillful.sh Aggregates Data from 50+ Directories
- MCP Server Registries Compared
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