bff-transport-boundary: Design & UI for AI Agents | OpenAgentSkill

Overview

Design and review Backend-for-Frontend transport boundaries. Use when implementing or changing request parsing, response mapping, streaming proxy behavior, CORS, header allowlists, authentication boundaries, timeouts, cancellation, error envelopes, or upstream orchestration.

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BFF Transport Boundary

Skill Interface

Name: bff-transport-boundary.
Description: Design and review Backend-for-Frontend transport boundaries for request parsing, response mapping, streaming proxy behavior, CORS, header allowlists, authentication boundaries, timeouts, cancellation, error envelopes, and upstream orchestration.
Parameters: BFF route or transport boundary, inbound request shape, upstream targets, authentication and authorization context, header policy, streaming behavior, timeout and cancellation rules, error envelope shape, and verification commands.
Instructions: Use this skill before implementing or changing BFF transport behavior. Keep orchestration and transport safety in the BFF, validate untrusted inputs, propagate cancellation, bound streaming resources, map errors explicitly, and verify success plus failure paths.

A BFF owns transport safety and orchestration. It should not absorb product reasoning, model prompts, workflow planning, or domain decisions that belong to backend services.

Ownership

The BFF owns:

Request parsing and runtime validation.
Authentication and authorization boundaries.
Header allowlists.
CORS and security headers.
Request-size limits and rate limits.
Timeout and cancellation propagation.
Upstream request orchestration.
Stream forwarding and backpressure.
Transport error mapping.
Request tracing and audit metadata.

The BFF does not own:

Model reasoning.
Prompt construction.
Agent planning.
Workflow graph routing.
Natural-language intent classification.
Tool implementation details.

Request Rules

Treat headers, cookies, query parameters, route parameters, body fields, multipart metadata, filenames, MIME types, and forwarded-address headers as untrusted.
Validate at the transport boundary.
Do not forward arbitrary inbound headers upstream.
Do not let clients control upstream hosts, internal URLs, authorization targets, trace ownership, or filesystem paths.

Streaming Rules

Do not buffer unbounded upstream streams in memory.
Respect backpressure.
Do not write after the response is closed or destroyed.
Release listeners, timers, and readers on every terminal path.
When the downstream client disconnects, abort upstream work when supported.

Define terminal reasons:

completed
client_cancelled
client_disconnected
bff_timeout
upstream_timeout
upstream_error
malformed_upstream_event
process_shutdown

Error Contract

Separate HTTP status, stable error code, developer message, user message key, retryability, and terminal reason.

Never expose stack traces, internal URLs, provider responses, authorization headers, cookies, tokens, or raw internal exception names.

Observability

Include request id, trace id, route, method, status, upstream target category, duration, bytes in/out, terminal reason, and error code where relevant.

Verification

Test success, invalid request, forbidden request, malformed upstream response, client disconnect, timeout, cancellation, upstream error, duplicate events, backpressure behavior, and cleanup of listeners and timers.

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File metadata

name: bff-transport-boundary
description: Design and review Backend-for-Frontend transport boundaries. Use when implementing or changing request parsing, response mapping, streaming proxy behavior, CORS, header allowlists, authentication boundaries, timeouts, cancellation, error envelopes, or upstream orchestration.

View original text

---
name: bff-transport-boundary
description: Design and review Backend-for-Frontend transport boundaries. Use when implementing or changing request parsing, response mapping, streaming proxy behavior, CORS, header allowlists, authentication boundaries, timeouts, cancellation, error envelopes, or upstream orchestration.
---

# BFF Transport Boundary

## Skill Interface

- Name: bff-transport-boundary.
- Description: Design and review Backend-for-Frontend transport boundaries for request parsing, response mapping, streaming proxy behavior, CORS, header allowlists, authentication boundaries, timeouts, cancellation, error envelopes, and upstream orchestration.
- Parameters: BFF route or transport boundary, inbound request shape, upstream targets, authentication and authorization context, header policy, streaming behavior, timeout and cancellation rules, error envelope shape, and verification commands.
- Instructions: Use this skill before implementing or changing BFF transport behavior. Keep orchestration and transport safety in the BFF, validate untrusted inputs, propagate cancellation, bound streaming resources, map errors explicitly, and verify success plus failure paths.

A BFF owns transport safety and orchestration. It should not absorb product
reasoning, model prompts, workflow planning, or domain decisions that belong to
backend services.

## Ownership

The BFF owns:

- Request parsing and runtime validation.
- Authentication and authorization boundaries.
- Header allowlists.
- CORS and security headers.
- Request-size limits and rate limits.
- Timeout and cancellation propagation.
- Upstream request orchestration.
- Stream forwarding and backpressure.
- Transport error mapping.
- Request tracing and audit metadata.

The BFF does not own:

- Model reasoning.
- Prompt construction.
- Agent planning.
- Workflow graph routing.
- Natural-language intent classification.
- Tool implementation details.

## Request Rules

- Treat headers, cookies, query parameters, route parameters, body fields,
multipart metadata, filenames, MIME types, and forwarded-address headers as
untrusted.
- Validate at the transport boundary.
- Do not forward arbitrary inbound headers upstream.
- Do not let clients control upstream hosts, internal URLs, authorization
targets, trace ownership, or filesystem paths.

## Streaming Rules

- Do not buffer unbounded upstream streams in memory.
- Respect backpressure.
- Do not write after the response is closed or destroyed.
- Release listeners, timers, and readers on every terminal path.
- When the downstream client disconnects, abort upstream work when supported.

Define terminal reasons:

- `completed`
- `client_cancelled`
- `client_disconnected`
- `bff_timeout`
- `upstream_timeout`
- `upstream_error`
- `malformed_upstream_event`
- `process_shutdown`

## Error Contract

Separate HTTP status, stable error code, developer message, user message key,
retryability, and terminal reason.

Never expose stack traces, internal URLs, provider responses, authorization
headers, cookies, tokens, or raw internal exception names.

## Observability

Include request id, trace id, route, method, status, upstream target category,
duration, bytes in/out, terminal reason, and error code where relevant.

## Verification

Test success, invalid request, forbidden request, malformed upstream response,
client disconnect, timeout, cancellation, upstream error, duplicate events,
backpressure behavior, and cleanup of listeners and timers.

Review the source

Skill source recorded

Skill instructions are recorded. This is not a runtime test, safety guarantee or compatibility certification.

Review before install: Avoid automatic install

License: MIT

Dependency or permission surface needs review
Permission surface may require sandboxing
Low GitHub adoption signal
AI review approval is missing
Quality score needs review
Permission surface needs review: secrets or environment access, shell or command execution
GitHub adoption: 28 GitHub stars
Stars/forks activity: 28 stars, 0 forks; issue activity unavailable in current metadata
Dependency/runtime risk: command execution surface, credential or environment access
Permission surface: secrets or environment access, shell or command execution
Review status: AI review approval is missing

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Source & usage notes

IndexedStatic Checked

Repository metadata and review signals are advisory. Popularity, source discovery and successful execution are different facts.

Source repository: HsienW/ai-agent-engineering-playbook
License: MIT
Version: Unknown
Last GitHub push: Sep 6, 2026
Registry updated: Sep 12, 2026
Instruction path: skills-contract-boundaries/bff-transport-boundary/SKILL.md @ 957a8bcdc457

Version reported in registry metadata; check source releases before relying on it.

Quality

56/100

Promising

Trust

Agent access

This page exposes the same decision, trust, audit, use-case, and install signals through the Registry API, so agents can rank this skill without scraping the UI.

Open install API LLM text format Open manifest Auto-resolve Plan

More details

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Creator: HsienW
Source: HsienW/ai-agent-engineering-playbook
Indexed by: OpenAgentSkill community index

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