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spec.agent ​

LLM-side configuration: which provider, which model, the system prompt, standard sampling knobs, and any MCP servers the agent connects to.

The whole block is optional. A2A does not require an LLM, so an agent can ship without one - just omit spec.agent entirely. Everything inside it is optional too, so a bare agent: {} is also valid.

yaml
spec:
  agent:
    provider: deepseek
    model: deepseek-v4-flash
    systemPrompt: |
      You are a professional customer support agent.
    maxTokens: 4096
    temperature: 0.3
    mcps:
      - name: filesystem
        transport: stdio
        command: npx
        args:
          - -y
          - "@modelcontextprotocol/server-filesystem"
          - /workspace
      - name: github
        transport: http
        url: https://mcp.example.com/github
        headers:
          Authorization: Bearer ${GITHUB_MCP_TOKEN}

provider ​

  • Type: string
  • Required: no
  • Allowed values: "", openai, anthropic, ollama, deepseek, google, mistral, groq.

The provider behind the LLM. The empty string is allowed for manifests that defer provider selection to deploy time.

New providers may be added in future minor schema versions. Consumers should be lenient about unknown values when reading newer manifests.

There is no API-key field here. provider and model select which LLM to use; the credential is injected at runtime as an environment variable by the generated project, never stored in the manifest. See Secrets & interpolation.

model ​

  • Type: string
  • Required: no

The model identifier for the chosen provider (e.g. gpt-4o-mini, claude-sonnet-4-7, deepseek-v4-flash). The schema doesn't constrain the value - providers move fast, and the model catalogue is consumer territory.

systemPrompt ​

  • Type: string
  • Required: no

The system prompt the agent boots with. Skills (see spec.skills) are injected on top of this prompt at startup, so keep systemPrompt focused on identity and ground rules, and put workflows into skills.

maxTokens ​

  • Type: integer
  • Required: no
  • Minimum: 1

Upper bound on tokens the model may emit per response. Optional - many runtimes default to a provider-specific value when omitted.

temperature ​

  • Type: number
  • Required: no
  • Minimum: 0
  • Maximum: 2

Sampling temperature. 0 makes the model maximally deterministic, 2 maximally creative. The clamp matches what most providers actually accept.

mcps ​

  • Type: array of MCP server objects
  • Required: no

MCP (Model Context Protocol) servers the agent connects to at runtime to discover and call external tools and capabilities, on top of the locally generated spec.tools. This is what bridges an A2A agent to the MCP ecosystem. It lives under spec.agent - rather than at the top of spec - because it only makes sense once an LLM is driving the agent.

Each entry takes:

  • name - required string. Identifier, unique within the agent. Pattern ^[a-zA-Z0-9_-]+$.
  • transport - required string. One of stdio, sse, http.
  • command - string. Executable to launch for a stdio server (e.g. npx, uvx, docker).
  • args - string[]. Arguments passed to command for a stdio server.
  • env - map[string]string. Environment variables for a stdio server (e.g. API keys it needs).
  • url - string. Endpoint URL for an http or sse server.
  • headers - map[string]string. Extra HTTP headers for an http or sse server (e.g. an Authorization header).
yaml
spec:
  agent:
    provider: openai
    model: gpt-4.1
    mcps:
      - name: filesystem
        transport: stdio
        command: npx
        args:
          - -y
          - "@modelcontextprotocol/server-filesystem"
          - /workspace
        env:
          LOG_LEVEL: info
      - name: github
        transport: http
        url: https://mcp.example.com/github
        headers:
          Authorization: Bearer ${GITHUB_MCP_TOKEN}

Only name and transport are required; the remaining fields are the connection details for the chosen transport. The schema intentionally does not enforce which combination is present for a given transport, so consumers stay lenient and decide how to resolve environment placeholders such as ${GITHUB_MCP_TOKEN} - see Secrets & interpolation for the convention and where credentials come from. New transport values may be added in future minor schema versions; consumers should tolerate unknown values when reading newer manifests.