{"slug": "postman-plugin-for-openai-codex", "title": "Postman Plugin for OpenAI Codex", "summary": "Postman launched the Postman plugin for OpenAI Codex, bringing Postman's agent skills into Codex sessions so the coding agent runs the Postman CLI instead of guessing at curl commands. The plugin installs either via the Postman CLI (npm install -g postman-cli, then postman init, requiring Node.js 18 or later) or through the Codex plugin marketplace (codex plugin marketplace add postmanlabs/postman-plugin), and both paths pull identical skill files from the postmanlabs/postman-plugin repository. The marketplace install also wires up the MCP server at mcp.postman.com so Codex tool calls against Postman are authenticated and traceable, with a free Postman account required only when pushing a mock or searching a workspace.", "body_md": "# Postman Plugin for OpenAI Codex\n\n[OpenAI Codex](https://developers.openai.com/codex/cli) has quickly become one of the most widely used coding agents out there, and it’s easy to see why: it writes real code, runs it, and keeps iterating until the tests pass. What Codex doesn’t know on its own is whether the API you’re calling actually behaves the way you think it does. It also has no way to tell whether a mock exists for the endpoint you haven’t built yet, or whether your team already solved this exact problem somewhere in a Postman workspace.\n\nThat’s why we’re thrilled to launch the [Postman plugin for Codex](https://github.com/postmanlabs/postman-plugin) today. It brings Postman’s agent skills straight into your Codex sessions. Ask it something like `@Postman turn this OpenAPI spec into a working mock server`, and it runs the actual Postman CLI underneath instead of Codex guessing at `curl` commands from memory. In this post, I’ll walk through the two ways to install it, then show two of the skills doing real work: discovering an API that already exists, and mocking one that doesn’t yet.\n\n## What you’ll need\n\n- [OpenAI Codex](https://developers.openai.com/codex/cli) (CLI, IDE extension, or the Codex app)\n- [Node.js](https://nodejs.org/) 18 or later, if you’re installing through the Postman CLI\n- A [Postman account](https://identity.getpostman.com/signup) (the free plan works, and it’s only required once you push a mock or search a workspace)\n\n## Two ways to install the plugin\n\nThe skill files live in one repository, [postmanlabs/postman-plugin](https://github.com/postmanlabs/postman-plugin), and every install path points back at the same `skills/` directory. That means the skills you get from the Postman CLI and the skills you get from the Codex plugin marketplace are identical. Pick whichever fits how you already work.\n\n### Option 1: Install with the Postman CLI\n\nIf you’d rather scaffold skills at the repository level, so both you and any headless agent working in that repo can use them, install [the Postman CLI](https://learning.postman.com/docs/postman-cli/postman-cli-installation):\n\n```\nnpm install -g postman-cli\n```\n\nThen, from a new or existing project:\n\n```\npostman init\n```\n\n`postman init` pulls the current skills from the [Postman skills repository](https://github.com/postmanlabs/skills) and writes them into your project, alongside `SKILL.md` files that tell Codex how and when to use them. It also links the repository to a Postman workspace, which is what `search` and `context-graph` need to find your team’s existing collections later. Skills drift over time, so check in on them with:\n\n```\npostman skills status\n```\n\nRun `postman skills update` when that command reports you’re behind. Add `--strict` in CI if you want a stale skill set to fail the build instead of quietly falling out of date.\n\n### Option 2: Install from the Codex plugin marketplace\n\nIf you’re working in a single Codex session and don’t need the skills committed to the repository, install the plugin directly:\n\n```\ncodex plugin marketplace add postmanlabs/postman-plugin\ncodex plugin add postman@postman\n```\n\nOr skip the terminal: open Codex, go to **Plugins**, search for “Postman,” and select **Add**.\n\n*The plugin listing shows what it can do before you install anything: build a collection and run tests, mock a spec, or score an API for AI-readiness.*\n\nThis path also wires up the [MCP server](https://modelcontextprotocol.io/) at `mcp.postman.com`, so tool calls Codex makes against Postman are authenticated and traceable back to the plugin, not just the skill files sitting on disk.\n\n## Say hello with @Postman\n\nHowever you installed it, Codex now resolves `@postman` as a mention, the same way it resolves a file path or a task:\n\n*Typing @postman in Codex surfaces the plugin the same way it surfaces files, tasks, and other plugins.*\n\nDescribe what you’re building, and the plugin recommends what it needs from there. You don’t have to know the underlying `postman` CLI commands. The skill files translate your request into the right ones and run them for you.\n\n## Find out if the API you need already exists\n\nBefore Codex writes an integration from memory, it’s worth checking whether the API already exists, either as something your team built or as a public API someone else maintains. That’s the [`api-discovery` skill](https://github.com/postmanlabs/postman-plugin/blob/main/skills/api-discovery/SKILL.md). It combines three things: `postman search` for anything already in your Postman workspaces, `context-graph` for how services depend on each other, and Orbit for public third-party APIs that need no signup or API key to search.\n\n```\n@Postman I'm adding email receipts to checkout. Does an API for\nsending transactional email already exist in our workspace, and\nif not, what public provider APIs would fit?\n```\n\nIf nothing turns up internally, the skill queries Orbit instead of guessing. Orbit’s `search` endpoint returns candidate public APIs, including what each one can’t do, not just what it can. Its `integrate` endpoint turns your chosen candidate into a task brief with auth requirements and known gotchas, using roughly 27 times less context than loading a full vendor OpenAPI spec. That matters more than it sounds: loading a vendor spec to answer “does this API support attachments” is a lot of context to burn on one yes-or-no question.\n\nBefore you let Codex act on a dependency question, ask it the blast-radius version too:\n\n```\n@Postman what depends on the billing-api collection, and what\nwould changing its response schema break?\n```\n\n`context-graph ask` reconciles Postman collections and specs with the GitHub repos and deployments connected through Agent Context, so the answer isn’t limited to what’s checked out locally. Treat what comes back as a lead worth verifying against source, not proof on its own; the graph refreshes nightly, so a service added yesterday won’t show up yet.\n\n## Mock the API before it exists\n\nThe second skill worth trying first is [`api-mocking`](https://github.com/postmanlabs/postman-plugin/blob/main/skills/api-mocking/SKILL.md). It stands up a fake backend from a collection or an OpenAPI spec, running locally as a plain Node process, with per-request overrides for testing failure paths without touching a real server.\n\nHere’s a real prompt and what Codex did with it:\n\n*One prompt, three mock scenarios, a git-native test collection, and a passing run, all from the api-mocking skill.*\n\n```\nAs part of the production readiness, I want to add local mocks\nto test everything. @Postman can you add these and run the\ninitial test suite.\n```\n\nThat produced three scenarios: `default`, `empty-catalog`, and `catalog-unavailable`. It also added a git-native collection with reusable assertions, an environment variable to point the running app at the mock instead of production, and `npm run mock:test` wired into the existing test suite. The run came back clean: 6 mocked requests, 16 assertions, 0 failures.\n\nOnce the mock is running, you can switch scenarios or send it to a teammate without writing a single Postman CLI command yourself. Just tell Codex what you need, like `@Postman switch the checkout mock to the empty-catalog scenario` or `@Postman push this mock so QA can hit it`, and the skill handles the rest.\n\n## Try it yourself\n\nInstall the plugin, then ask it something specific instead of something generic:\n\n- `@Postman does an API for [thing you're about to build] already exist in our workspace?`\n- `@Postman turn this OpenAPI spec into a mock server with a scenario for a 500 error`\n- `@Postman is this API agent-ready?`\n\nThe last one runs the [`ai-readiness` skill](https://github.com/postmanlabs/postman-plugin), which scores a collection or spec on exactly the kind of thing that makes this whole plugin worth having: whether an agent calling your API can recover when something goes wrong, not just when everything works.\n\n## Resources\n\nInstall the plugin now, and let me know what the first thing you asked it to do was.", "url": "https://wpnews.pro/news/postman-plugin-for-openai-codex", "canonical_source": "https://blog.postman.com/postman-plugin-for-openai-codex/", "published_at": "2026-09-29 17:00:04+00:00", "updated_at": "2026-09-29 17:19:45.437253+00:00", "lang": "en", "topics": ["ai-agents", "ai-tools", "developer-tools", "agent-protocols"], "entities": ["Postman", "OpenAI Codex", "Postman CLI", "postmanlabs/postman-plugin", "Model Context Protocol", "Node.js", "mcp.postman.com"], "also_reported_by": [], "alternates": {"html": "https://wpnews.pro/news/postman-plugin-for-openai-codex", "markdown": "https://wpnews.pro/news/postman-plugin-for-openai-codex.md", "text": "https://wpnews.pro/news/postman-plugin-for-openai-codex.txt", "jsonld": "https://wpnews.pro/news/postman-plugin-for-openai-codex.jsonld"}}