Overview
FreeAgent .NET Client is an open-source library for talking to the FreeAgent API from modern .NET.
I was far from impressed with the existing .NET libraries on NuGet for working with the FreeAgent API, and I needed a client that behaved like a proper SDK (i.e. OAuth 2.0 with token refresh, respect for rate-limit headers, bounded retries, typed errors, and pagination) for an upcoming FreeAgent based project. So I decided to write my own. Coverage is still a bit limited at this point: Company and Contacts are in first, and the public API is still in prerelease.
It targets .NET 8 and .NET 10, is fully async, and ships with XML docs. If you are wiring FreeAgent into a .NET app and do not want to re-solve OAuth and HTTP transport, this is the starting point I wished existed. And hopefully before too long it will be a bit more complete with the rest of the FreeAgent API calls.
Technologies Used
- C# / .NET 8 and 10: multi-targeted client library.
- OAuth 2.0: authorization URL, code exchange, and automatic refresh.
- HttpClient: rate-limit headers,
Retry-After, exponential backoff. - xUnit: automated tests across both target frameworks.
Key Features
- OAuth helper:
FreeAgentOAuthClientfor the authorization code flow. - Typed exceptions: rate limit, OAuth, and general API errors instead of raw HTTP.
- Pagination: single page or
IAsyncEnumerableauto-pagination for contacts. - Safe retries: GET/DELETE by default; mutating methods opt in.
- Company API: company details, business categories, tax timeline.
- Contacts API: paged list and full auto-pagination.
Repository
👉 GitHub Repo
A library rather than an app: the unglamorous plumbing that makes FreeAgent usable from .NET without copying the same OAuth and retry code into every project.