danger: failed to evaluate Dangerfile: undefined method

TL;DR

The Dangerfile calls a method that isn't defined - usually a typo or a plugin gem that isn't installed. Read the method name and line number from the error, add or fix the plugin, and re-run Danger exactly the way CI does. The evaluation context only knows the built-in DSL plus loaded plugins, so anything else is "undefined".

The error

danger: failed to evaluate Dangerfile: undefined method

Steps to fix

1. Read the full error: it names the undefined method and the Dangerfile line - open that line.

• Expected: a single method call that doesn't match anything in the DSL.

1. Check whether the method comes from a plugin: look for the plugin gem in the Gemfile (Ruby Danger) or the import at the top of the Dangerfile (JS Danger); if it's missing, add it.

• Expected: you can say whether the method should exist via a plugin or is simply a typo.

1. Make sure the plugin actually loads in CI: Ruby Danger loads plugins through the Gemfile and bundler, so re-run with the same bundler setup CI uses; confirm the lockfile includes the plugin.

• Expected: local reproduction uses the identical dependency set as CI.

1. Run Danger locally the way CI does.

• Expected: the Dangerfile evaluates cleanly and posts its comment.

Use this when

• The Danger step fails in CI with "failed to evaluate Dangerfile: undefined method".
• A Dangerfile was just edited or a plugin was just added.
• Danger works locally but fails in CI (dependency drift).

Not for this skill when

• Danger fails to post its comment rather than to evaluate (that's auth or API permissions).
• The error is a syntax error rather than an undefined method (fix the Ruby/JS syntax).
• You're on danger-swift (different toolchain, different fix).

Variant phrasings

• dangerfile undefined method error
• danger failed to evaluate dangerfile
• danger ruby NoMethodError in CI
• danger plugin method not found

Why it happens

A Dangerfile runs inside a DSL context: every method call must resolve against that context or a loaded plugin. A typo'd method name, a plugin gem that's in the docs but not in the Gemfile, or a lockfile that doesn't include the plugin all produce exactly this error at evaluation time. CI's clean install surface makes it stricter than a developer's machine with globally installed gems.

Edge cases

• danger-js and danger-ruby have different DSLs - confirm which one CI runs before trusting a method name from the other one's docs.
• Plugin version drift: a method that exists in the plugin's latest release may not exist in the version pinned in the lockfile.
• Methods removed in a Danger major version: check the changelog when upgrading Danger itself.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ZFzE96ak5DYIANRfNrg3lw