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Penify.dev vs Swimm

Two fact sheets from our own research, side by side — pricing, platforms, API access and status re-checked by us rather than quoted from the vendors. Penify.dev publishes a starting price ($18); Swimm does not. Only Penify.dev has a free tier.

Penify.devWrites docstrings and inline documentation from your code changes via CLI, git hook, or GitHub App.SwimmStatic analysis plus AI that reads legacy code and writes the documentation and diagrams a migration team needs.

Side by side

FactPenify.devSwimm
CategoryDocumentation GeneratorsDocumentation Generators
Pricing modelFreemiumContact
Starts at$18 month—
Public APINoNo
PlatformsWebWeb, Vscode Ext
CompanyPenify.devSwimm
Launched—2019
Last verifiedSep 1, 2026Sep 6, 2026

What our research says

Penify.dev

Penify.dev focuses narrowly on the least glamorous documentation task — writing docstrings for the functions inside a diff — instead of trying to generate whole READMEs or wikis. That focus makes it easy to bolt onto an existing pull-request workflow, but it also means it does not replace higher-level documentation tools, and the free tier's per-file cap on private repos pushes active teams toward a paid plan quickly.

Pros

  • Comments directly on pull requests through a GitHub App instead of requiring a separate tool to check
  • Works via CLI or git hook for teams that don't want a GitHub-specific integration
  • Free tier is usable for public repositories without a credit card

Cons

  • Private repo usage on the free tier is capped by file count, which active codebases will exceed quickly
  • Limited to a fixed set of supported languages rather than open-ended code coverage
  • Only documents inline code, not higher-level architecture or user-facing docs

Swimm

Swimm is the rare documentation tool that treats old code as the source of truth instead of asking humans to describe it. If you are staring at a COBOL or .NET estate nobody understands, the flow maps and extracted business rules are the useful part. The catch is that it is no longer a tool you can simply buy: it is a staged engagement with engineers attached, and the self-serve documentation product it was known for is not what the site sells today.

Pros

  • Deterministic static analysis backs the AI output, so traces come from the code rather than a guess
  • Produces diagrams and flow maps, not only prose
  • Covers mainframe and COBOL alongside .NET and Java
  • Work is broken into fixed-price stages you can stop after

Cons

  • No pricing published anywhere on the site
  • Repositioned away from the continuous-documentation product it was known for
  • Aimed at large estates, which makes it overkill for a normal repository

Which one fits

Choose Penify.dev if you need

  • Teams that want docstrings kept current automatically as pull requests land
  • Open source maintainers documenting public repositories for free
  • Developers who prefer a git hook or CLI over a separate documentation dashboard

Choose Swimm if you need

  • Teams documenting a mainframe or legacy .NET/Java estate before a migration
  • Architects who need job-flow and variable traces out of unfamiliar code
  • Enterprises that want non-engineers to read what the code actually does

More comparisons

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