generated: '2026-08-13'
method: probed
source: https://docs.cello.so/.well-known/agent-card.json
discovery:
  path: /.well-known/agent-card.json
  canonical: true
  host: docs.cello.so
  note: >-
    The card is served from Cello's own documentation host, docs.cello.so, at the canonical
    A2A 1.0 path. The legacy /.well-known/agent.json path 404s on the same host, and every
    other Cello host probed (cello.so, api.cello.so, mcp.cello.so) 404s on both paths, so
    docs.cello.so is the single origin serving it.
conformance:
  spec: A2A 1.0.0
  grade: conformant
  protocol_version: '0.3'
  preferred_transport: HTTP+JSON
  hard_checks:
    capabilities_is_object: true
    protocol_version_present: true
    skills_is_array: true
  optional_checks:
    preferred_transport_present: true
    default_input_modes_present: true
    default_output_modes_present: true
  deviations:
  - protocolVersion-0.3-predates-a2a-1.0.0
  - supportedInterfaces-instead-of-additionalInterfaces
  - interface-uses-protocolBinding-instead-of-transport
  - no-root-description-field
  - skills-tags-empty-array
  - url-points-at-documentation-site-not-an-a2a-message-endpoint
card:
  name: Cello
  url: https://docs.cello.so/
  version: 1.0.0
  provider_organization: Cello
  documentation_url: https://docs.cello.so/
  capabilities:
    streaming: false
    pushNotifications: false
  default_input_modes:
  - text/plain
  default_output_modes:
  - text/plain
  skills: 1
  file: cello-agent-card.json
skills:
- id: cello
  name: Cello
  url: https://docs.cello.so/.well-known/agent-skills/cello/skill.md
  http_status: 200
  saved_to: ../skills/cello-referral-integration.md
  note: >-
    The card's single skill resolves to a real, 13,290-byte Agent Skill markdown document
    published by Cello. It is saved verbatim in skills/ rather than being restated here.
x-notes:
  generator: >-
    The card and the skill it points at are produced by Cello's Mintlify documentation project
    (metadata.mintlify-proj = cello in the skill frontmatter), so the agent surface is
    documentation-shaped: it describes how to integrate Cello, and does not itself accept A2A
    tasks. The card's url is the docs site, not a message endpoint.
  relationship_to_mcp: >-
    Cello's executable agent surface is the hosted MCP server at https://mcp.cello.so/mcp
    (OAuth-gated, see mcp/cello-mcp.yml). The agent card does not advertise it.
findings:
- id: linked-skill-serves-a-403-script-url
  severity: high
  detail: >-
    The Agent Skill this card points at instructs agents to load Attribution JS from
    https://assets.cello.so/attribution/latest/attribution.js (and the sandbox equivalent). That
    URL returns 403. Cello's human-facing docs use cello-attribution.js, which returns 200. The
    machine-readable path and the human path disagree, and only the machine one is broken.
  evidence:
  - url: https://assets.cello.so/attribution/latest/attribution.js
    status: 403
  - url: https://assets.cello.so/attribution/latest/cello-attribution.js
    status: 200
- id: card-advertises-no-executable-endpoint
  severity: medium
  detail: >-
    Every URL in the card — url, provider.url, documentationUrl and supportedInterfaces[0].url —
    is https://docs.cello.so/, the documentation site. Cello's actual agent-callable surface, the
    OAuth-gated MCP server at https://mcp.cello.so/mcp, is not referenced anywhere in the card. An
    A2A client that resolves this card gets documentation, not a task endpoint.
x-evidence:
  fetched: '2026-08-13'
  url: https://docs.cello.so/.well-known/agent-card.json
  http_status: 200
  content_type: application/json
  bytes: 1030
  also_probed:
  - {url: 'https://docs.cello.so/.well-known/agent.json', http_status: 404}
  - {url: 'https://cello.so/.well-known/agent-card.json', http_status: 404}
  - {url: 'https://cello.so/.well-known/agent.json', http_status: 404}
  - {url: 'https://api.cello.so/.well-known/agent-card.json', http_status: 404}
  - {url: 'https://api.cello.so/.well-known/agent.json', http_status: 404}
  - {url: 'https://mcp.cello.so/.well-known/agent-card.json', http_status: 404}
  - {url: 'https://mcp.cello.so/.well-known/agent.json', http_status: 404}