The plugin index is split into a handful of categories so you do not have to read every repository to learn the shape of the ecosystem. The categories are ours. Publishers do not file their own taxonomy with us in a formal way, and a plugin can sit near a boundary. Use the category as a first cut, then confirm on the repository.
Client
Client plugins change how you look at Harness and how you trigger it. Sidebars, terminal interfaces, balance widgets, and marketplaces live here. Install one client plugin when the default UI is the thing that slows you down. Do not install three of them to "try the look." They draw on the same window. The better sidebar, the TUI, the marketplace, and the balance widget are all client plugins, and they solve different annoyances: peeking at files, preferring a terminal, discovering other plugins, and noticing you are about to run out of API balance.
A client plugin that can run commands is an automation tool wearing a UI. Read which commands it exposes before you leave it running beside a repository you do not want rewritten.
Model inference
Model Inference plugins sit between you and the model. Some route a long job across models so a cheaper model drafts and a stronger one checks. Some, like image adapters, let a text-only chat model see a screenshot. This category can change your bill and the host that receives your code. Treat a routing configuration as production config. Write down which model handles which step, and try it on a public sample before you point it at client source.
If you only wanted to compare models on paper, you do not need a plugin. Use Compare and the guide on deciding after a comparison.
Workflow
Workflow plugins are about the shape of the agent's work: checks, contracts, gates before a change lands. They are the right category when the agent edits the right files but drifts from a rule you care about. They are the wrong category when the agent cannot see the file at all. That is a client or inference problem. A workflow plugin will not fix a model that never received the diff.
Expect these plugins to slow a careless loop down on purpose. If a plugin's entire pitch is "never stop to ask," it does not belong in your mental model of this category, whatever the card says.
Memory
Memory plugins persist notes between sessions: decisions, glossary, files that matter. They help on a codebase you return to for weeks. They hurt when they replay a stale decision as if it were still true, or when they store snippets of secrets because the agent pasted a token into the note. Read what gets written and where the store lives. A memory file inside the repository will be committed if you are not careful. A memory file outside the repository will surprise you on a different machine.
One memory plugin is enough. A second one gives you two biographies of the project, and the agent will quote the wrong one with equal confidence.
Web tools
Web Tools fetch or search the web from inside the agent. They are useful when the task depends on a current document you can name. They are a distraction when the task is entirely inside the repository and the plugin keeps leaving to browse. Turn them on for the session that needs them. A web tool plus a prompt that says "always look it up" will cite pages the model did not actually open. Ask it to quote the sentence it used.
Security and admin-security
Security and admin-security are not the same claim. One group tends to be defensive checks around the agent. The other includes offensive or stress-test tooling aimed at model behavior. Read the README twice. A tool that generates attacks does not make your application safer merely by being installed. Run it only against systems you are allowed to test, and do not point it at a customer's host because the card said "security."
Fun and dress-up
Fun & Dress-up is optional decoration. It should not require API keys, and it should not sit in the path of your deploy. If a cosmetic plugin asks for the same permissions as a workflow plugin, close it.
Using the categories together
A reasonable stack is one client surface, one inference path, and either memory or a workflow check. Add web tools only for tasks that need them. Leave security tooling for a separate session. The plugin guide describes the install order. The category you open first should be the annoyance you can name today, not the category with the most stars.
Boundaries that look like overlaps
A balance widget in Client shows you a number from the vendor account. It does not route the prompt. If the number is wrong, you fix the widget or the account, not the inference plugin. A routing plugin in Model Inference can spend the balance the widget displays. Installing both is reasonable once each one has passed a separate test. Installing them on the same afternoon means you will not know which one emptied the account.
A memory plugin that records "we deploy on Fridays" will keep saying that after you move to Tuesdays. A workflow plugin that blocks Friday deploys will block the new Tuesday process if its rule was copied from the memory note. Read the stored rule when the process changes. Delete the sentence. Do not add a third plugin to override it.
Web tools and security tools both "go look at things." Web tools fetch a page you named. Security tools that generate attacks are aimed at a system under test. Pointing a web tool at your own docs is ordinary. Pointing an attack generator at a host you do not own is not, whatever the category chip on our card implies. When the README and the chip disagree, follow the README and tell us. The chip is our sorting. The README is the publisher's behavior.
Fun and dress-up should be removable without uninstalling the client you depend on. If a theme is bundled inside a sidebar fork, you did not install a theme. You forked your client. Treat that repository as the client category even if the description talks about colors.
How to leave a category
If you opened Memory because the agent forgot a decision, try writing the decision in a file the agent already reads, such as a short project note, before you install persistence you must curate. If that file is enough, you do not have a memory-plugin job. If you opened Workflow because one edit was wrong, try a single review prompt on the diff before you install a gate. The heavier tool is for the repeated failure, not the first one. Your first week is organized around that delay on purpose. When you do add the heavier tool, write down which repeated failure it is for, in one sentence, next to the GitHub URL. If you cannot write the sentence a week later, uninstall. The category page will still be there, and the introduction at the top of it will still tell you what the shelf is for. A plugin kept "because the category seemed important" is how stacks become unreadable. Leave the shelf after the job is named, not after the star list is exhausted.