Borrowing it
Nothing to install: this file belongs to contentful/ui-extensions-sdk. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/contentful/ui-extensions-sdk/main/AGENTS.mdgit clone --depth 1 https://github.com/contentful/ui-extensions-sdkWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/instructions/contentful/ui-extensions-sdk/agents-md)<a href="https://agentmods.dev/instructions/contentful/ui-extensions-sdk/agents-md"><img src="https://agentmods.dev/badge/instructions/contentful/ui-extensions-sdk/agents-md/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/contentful/ui-extensions-sdk/agents-md"><img src="https://agentmods.dev/badge/instructions/contentful/ui-extensions-sdk/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.02020 | $0.02020 |
| Opus 5.5 | $0.00808 | $0.00808 |
| Sonnet 5.5 | $0.00404 | $0.00404 |
| Haiku 4.5 | $0.00202 | $0.00202 |
Grade A, and why
ui-extensions-sdk AGENTS.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Guide — ui-extensions-sdk
Identity
This is the ui-extensions-sdk repository (github.com/contentful/ui-extensions-sdk). It builds and publishes the App SDK to npm under two package names: @contentful/app-sdk (preferred — use this in all new code, examples, and documentation) and contentful-ui-extensions-sdk (legacy alias retained for installed-base compatibility). Repo name and package names diverged for historical reasons; do not rename the repo.
Ownership
@contentful/group-applied-ai-solutions (co-owned per .github/CODEOWNERS).
Where to look
| You want to… | Read this |
|---|---|
| Understand the runtime + build pipeline | ARCHITECTURE.md |
| Develop locally / run tests / open a PR | CONTRIBUTING.md |
| See the consumer-facing reference | Contentful Docs — App SDK Reference |
Sharp edges (do not violate)
-
Public types are a contract. Changing or removing any export from
lib/types/index.tsis a breaking change. Hundreds of customer apps and many internal Contentful repos consume these types. A breaking change requires afeat!:commit +BREAKING CHANGE:footer (the major bump is otherwise silently dropped without the footer). -
Bundle size is policed by CI.
npm run sizereports gzipped bytes ofdist/cf-extension-api.jsafter every build. Adding a runtime dependency or a heavy utility is almost always the wrong move —contentful-managementis currently the only runtime dep. Re-implementing a small helper inline beats pulling in a package. -
PostMessage is the only transport. All host communication routes through
lib/channel.ts. Do not add direct DOM,fetch, or global-window access for host operations. If you need a new capability from the host, add a method on the channel and contract its protocol with the web app team.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago Changed · -7 tokens per session b356c56560cc
- 2mo ago First seen · 96 lines · 2,027 tokens per session scan A 0869060ed82c
ui-extensions-sdk AGENTS.md is an instructions file published in the GitHub repository contentful/ui-extensions-sdk (131 stars, last pushed 3d ago), licensed MIT. It adds 2,020 tokens to every session, about $0.0081 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
ui-extensions-sdk AGENTS.md compared with instructions from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| ui-extensions-sdk AGENTS.mdcontentful/ui-extensions-sdk | Instructions file | 131 | 3d ago | MIT | A | 2,020 | Codex, OpenCode |
| vscode buildNext.instructions.mdmicrosoft/vscode | Instructions file | 195k | yesterday | MIT | A | 9,719 | GitHub Copilot |
| next.js AGENTS.mdvercel/next.js | Instructions file | 143k | yesterday | MIT | A | 7,461 | Codex, OpenCode |
| langchain AGENTS.mdlangchain-ai/langchain | Instructions file | 149k | yesterday | MIT | A | 4,680 | Codex, OpenCode |
| vscode oss-third-party-notices.instructions.mdmicrosoft/vscode | Instructions file | 195k | yesterday | MIT | A | 5,516 | GitHub Copilot |
| vscode copilot-instructions.mdmicrosoft/vscode | Instructions file | 195k | yesterday | MIT | A | 3,093 | GitHub Copilot |
| deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness | Instructions file | 274k | 2d ago | MIT | A | 4,313 | Codex, OpenCode |