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A tool node fetches a raw PR diff from the GitHub API, then an agent summarizes the changes. Demonstrates how to chain an HTTP tool node with a downstream agent node using a real external API.

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What it demonstrates

  • tool node with tool: http for external API calls
  • Template interpolation in HTTP headers ({{ env.GITHUB_TOKEN }})
  • Chaining a tool node to an agent node via an edge
  • Passing fetched data through the workflow context to a downstream agent

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Prerequisites

Set a GitHub personal access token with repo:read scope: 
export GITHUB_TOKEN=ghp_...

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Run it

sirenspec run docs/cookbook/pr-summarizer/workflow.yaml \
  --input "Summarise this pull request for me."
To point at a different PR, edit the url in workflow.yaml to match your repository and PR number: 
https://api.github.com/repos/{owner}/{repo}/pulls/{number}

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Workflow

docs/cookbook/pr-summarizer/workflow.yaml
version: "0.1"

agents:
  summarizer:
    model: "openai:gpt-4o-mini"
    system: |
      You are a senior software engineer reviewing a GitHub pull request.
      You will be given the raw unified diff of the pull request.
      Write a concise, developer-friendly summary covering what changed,
      why the change is likely being made, and any notable risks.
      Keep the summary under 200 words.

nodes:
  fetch_diff:
    type: tool
    tool: http
    config:
      url: "https://api.github.com/repos/sirenspec/sirenspec/pulls/1"
      method: GET
      headers:
        Authorization: "Bearer {{ env.GITHUB_TOKEN }}"
        Accept: "application/vnd.github.v3.diff"
        User-Agent: "sirenspec/0.1"
      timeout: 15
    output_key: diff

  summarize:
    agent: summarizer
    writes: output.summary

edges:
  - from: fetch_diff
    to: summarize

guardrails:
  - injection

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Graph

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Next steps

Tool Nodes

Full HTTP and Python tool node documentation.

Blind Code Review

Multi-turn refinement: write, review, revise.