nomoat / Callosum / Alternatives

Alternatives to Callosum

Callosum: Desktop app for designing, calling and documenting APIs that keeps an OpenAPI spec in sync, offline with no login. Here are 6 other products that do a similar job. Of these, 4 have a free plan.

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  Routebase

  Keeps API specs, mock servers, tests and published docs in step from a single spec, for software teams.

  Since 2026

  Free plan · Developer tools · Developers

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  SpecShield

  Compares your OpenAPI spec on each pull request and blocks merges that would break the services using your API.

  Since 2026

  Free plan · Developer tools · Developers

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  APIndex

  A catalog engineering teams host themselves to collect REST and SOAP specs, see which services depend on which, and try out endpoints.

  Since 2026

  Subscription · Developer tools · Developers

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  Mockfly

  Frontend teams can spin up hosted fake REST endpoints, import OpenAPI or Postman files, and fill responses with fake data.

  Free plan · Developer tools · Developers

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  Echolon

  Open-source API client that keeps collections as local files synced through Git, for testing REST and WebSocket APIs offline.

  Free plan · Developer tools · Developers

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  Yaak

  A desktop app for sending and testing REST, GraphQL, gRPC and WebSocket requests, stored locally and synced through Git.

  Since 2025

  Subscription · Developer tools · Developers