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API client generation with coding agents
September 25, 2026 - 2 minute read
API client generation turns a service contract into repeatable client code, documentation, and models. Coding agents can coordinate the update across a specification, generator configuration, and tests. The result stays reviewable only when the contract remains the source of truth and generated output is never hand-edited.
OpenAPI Generator provides client generators for many languages and can run through a CLI or build plugin. Its breadth makes pinning important. A generator upgrade can change naming, serialization, dependencies, and formatting even when the API contract stays the same.
Bound the API client generation task
Start with the reviewed OpenAPI document, target language, generator name, generator version, configuration file, and exact command. State which generated directory may change and whether generated files are committed or published as a package.
Separate contract changes from generator upgrades when possible. If both move in one pull request, reviewers cannot easily tell whether a diff came from an API decision or a tooling change. When an endpoint changes, classify it as additive, deprecated, or breaking before regeneration.
Factory’s AGENTS.md guidance supports repository-scoped commands and completion checks. Put the canonical generation command and the rule against hand edits near the generated directory so a coding agent encounters them before making changes.
Validate generated API clients
Run a clean generation and confirm that a second run produces no diff. That check catches hidden timestamps, unpinned templates, and local configuration. Review the generated diff for public method names, required fields, nullability, enum behavior, authentication handling, and dependency changes.
Compile the client and run contract-focused tests against a controlled server or mock. Test representative success and error responses, optional fields, pagination, and serialization boundaries. A successful generator command proves only that files were emitted.
Compare the contract against the previous released version. Existing consumers may depend on behavior that remains valid in the server but changed in one generated language. The OpenAPI Generator usage guide documents the available invocation methods, which should be reduced to one repository-approved command.
Review API client generation as a release
Generated volume can hide a small consequential change. Ask the agent to summarize the contract delta, generator delta, dependency delta, and validation results separately. Keep the raw generated diff available, but give reviewers a short map to the files that define public behavior.
Use CI to regenerate and fail when committed output is stale. Factory’s Droid Exec can run the repository command non-interactively, while deterministic compile and contract checks remain required gates. An independent review should inspect handwritten templates or configuration with the same care as application source.
Choose the client package version from the compatibility impact, not from the size of the generated diff. Publish only after the contract and generated artifact are both approved. If multiple language clients share one contract, update them in coordinated, separately testable changes rather than assuming one successful target proves the rest.
