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title MCP servers
description Connect Model Context Protocol servers, local or remote, with progressive injection and per-tool filters.

Aster speaks the Model Context Protocol. Servers are declared under mcp.servers in aster.yaml:

mcp:
  servers:
    github:
      command: npx
      args: ["-y", "@modelcontextprotocol/server-github"]
      env:
        GITHUB_TOKEN: ${GITHUB_TOKEN}
    docs:
      url: https://docs.example.com/mcp
      headers:
        Authorization: Bearer ${DOCS_TOKEN}

command + args + env spawn a local server over stdio; url connects to a remote one over streamable HTTP (type: sse for the deprecated HTTP+SSE binding, http accepted as an alias). disabled: true skips a server without deleting its config.

Two other sources add servers after the yaml is read: .mcp.json in the repo root and ~/.aster/mcp.json are read natively, and installed plugins contribute theirs as <plugin>/<server>. Both only fill names aster.yaml did not already define, so the yaml always wins a collision.

Progressive injection

Tool inventories can be huge, so Aster does not paste them all into context. The inventory is measured against a budget (mcp.context_tokens times mcp.inventory_percent, default 1.5% of 100k). Within budget, tools are listed in the prompt. Above it, the prompt lists servers only, and the model discovers tools with a search call. Either way the agent finds the tool; the difference is how much context it costs.

Filtering tools

mcp:
  tools:
    allow: []          # empty means every tool
    deny:
      - "web/crawl"
      - "browser/*"

Globs match against the server/tool id, and deny wins over allow. The filter runs after every server has listed, so it covers the built-in web server as well as third-party ones.

Managing from the shell

aster mcp list [--no-connect]
aster mcp enable NAME | server/tool
aster mcp disable NAME | server/tool     # globs allowed
aster mcp import [--from claude|codex|cursor|opencode|hermes]
aster mcp remove [NAME]
aster mcp login NAME                     # OAuth for a remote server

/mcp in chat shows the same picture and connects servers if the session started with --no-mcp.

WebMCP

mcp.webmcp bridges tools a web page registers in your own Chrome. Start Chrome with --remote-debugging-port=9222 and the page's tools appear as MCP tools.