Reviewed 6 October 2026. Product statements are grounded in the linked documentation. Workflows and fictional examples are editorial guidance.
Original AI-generated concept illustration.
Build an extension around a narrow task
An agent that can write code can also help draft an extension for its own environment. That is useful when you repeatedly need a small capability: convert a brief into a structured file, extract fields from approved notes, or prepare a local review report. The important distinction is between generated code and a verified extension. A convincing explanation of how a plugin works does not establish that it loaded correctly, handled errors, or stayed within the intended project.
DeepSeek Harness is an open-source project organized around plugins. Its official repository identifies the software as a developer preview with possible compatibility changes. Use its current developer and architecture documentation as the authority for plugin interfaces. The process below is a proposed method for building and reviewing a small extension. It does not claim that every release includes a particular one-click plugin generator or that generated code is ready for unattended operation.
Documentation: DeepSeek Harness official repository.
Define the contract in ordinary language
Start with a brief that another developer could implement without guessing. For example: read a selected Markdown brief and produce a JSON review file beside it. Define the required fields, allowable input size, output filename, and behavior when the file already exists. State which folder is in scope. Describe errors as part of the contract: missing input, malformed data, unsupported encoding, and permission failure. These requirements are more useful than asking for a powerful productivity plugin.
Separate transformation from side effects. The transformation reads a brief and returns structured information. The side effect saves that information to disk. Keeping them distinct makes testing easier and reduces the chance that a partial result overwrites an accepted file. Specify whether the plugin should return a preview before saving. For a first version, prefer explicit filenames and a small input format rather than trying to support every document type at once.
Supply the current documentation
Ask the coding assistant to read the relevant official plugin documentation before producing an implementation. Give it the actual repository version you use. If an interface is unclear, require it to identify the missing detail instead of inventing a method name. Documentation for another release may be close enough to look plausible while still producing code that fails at startup. Keep the source reference alongside the generated implementation so future repairs have a clear starting point.
A useful prompt is: create a minimal plugin for this installed version, explain its entry point and configuration, and include a local example that does not require external credentials. Ask it to state assumptions separately from confirmed interfaces. Request only the dependencies the narrow task needs. If a package is added, check why it is necessary and whether the same transformation could use functionality already available in the project.
Review the generated implementation
Read the registration and configuration first. Confirm that the plugin advertises the action you intended and uses the current interface. Then inspect file access, network activity, process execution, and error handling. Search for placeholder values and unexplained imports. Check whether output paths are constructed safely from a selected project directory. A plugin intended to generate a local review file should not need an unrelated remote service or access to an entire home directory.
Review the user-facing result as carefully as the code. Error messages should explain the failed condition without exposing credentials or dumping unrelated content. A success message should point to an output that actually exists. If the action is a preview, label it as a preview. If a field could not be extracted, preserve that uncertainty instead of filling it with a plausible value. Those details determine whether someone can rely on the plugin during ordinary work.
Test the transformation before the integration
Create a tiny sample brief with a title, audience, deadline, and one deliberately missing field. Compare the generated JSON with an expected result written by hand. Repeat with unusual punctuation, a long paragraph, and an empty file. These cases test the contract rather than merely running the happy path. Verify that the transformation preserves source meaning and does not infer facts that were never provided. If the action uses a model, also test how uncertainty is represented.
Next test the saving behavior in a disposable directory. Run the action twice and confirm that the second run follows the overwrite rule. Try an invalid path and a read-only location. Check whether a failure leaves behind a partial file. If an output contains structured data, parse it with an ordinary parser rather than judging it visually. A file that resembles JSON may still contain invalid syntax, duplicated fields, or unexpected text around the object.
Load the plugin and verify the whole task
Follow the current project's development instructions to load the extension. Confirm that it appears, that configuration reaches it, and that the actual agent action calls the expected implementation. Run the same sample used in the earlier test. Compare the integrated output with the accepted baseline. If the result differs, investigate the integration boundary before changing the transformation. A correct function can still behave incorrectly when the wrong input or project context reaches it.
Keep an execution note containing the installed version, configuration, sample input, and observed output. Avoid declaring support for a platform you did not test. A desktop installation and a web interface may expose different behaviors. If you only validated the local transformation and one launch route, say so in the plugin's README. Honest support boundaries make the extension easier to use and reduce the time spent chasing failures in environments it never claimed to cover.
Turn a working draft into a maintainable plugin
Once the basic action works, improve discoverability and documentation. Explain what the plugin does, how to configure it, and what it intentionally leaves to the user. Include the expected output and a recovery procedure. Store accepted examples beside the source code. When a preview release changes an interface, rerun those examples before updating the team setup. Keep the last working version available until the new version produces the same reviewed result.
Add features according to observed need. If users repeatedly ask for a second output format, define its contract before implementing it. If the same field is ambiguous, improve the source brief rather than teaching the plugin to guess. Avoid turning a small extension into a general automation platform. A dependable plugin with one well-defined job is more valuable than a large collection of actions that nobody can explain or repair.
Frequently asked questions
Can an agent create a plugin without human review?
It can draft code, but review and execution checks establish whether the result works. Treat generated implementations as changes to verify, especially when they read files or perform actions.
What should my first plugin do?
Choose a narrow local transformation with a clear input and output. A brief-to-review-file action is easier to test than a workflow that sends messages, modifies accounts, and publishes content.
Why does the installed version matter?
Developer-preview interfaces can change. Record the version and use the corresponding documentation so an apparently valid implementation does not depend on an obsolete interface.
How should I handle missing input facts?
Represent them explicitly as unknown or missing. Do not invent deadlines, owners, or commitments to make a structured result look complete.
Resources and related articles
Continue with DeepSeek Harness Desktop: Plan Repeatable Agent Workflows, Claude Code Mods, Skills, Hooks and MCP: Choose the Right Extension, or Gemini for Coding: Debug Small Reproducible Problems.
