Netlify Dev environment variable precedence across local .env, UI settings, and function runtimes

Question

GoalDetermine the exact precedence order Netlify Dev uses when resolving environment variables for both Netlify Functions (Node.js) and Edge Functions (Deno) during local development, so that integration tests can reliably mirror production behavior without deploying.Constraints and uncertaintyNetlify Dev sources variables from a local .env file, the linked site's UI settings (via netlify link or netlify env:get), and the CLI's own configuration. The documentation does not specify a universal precedence rule that applies to every runtime context—especially the divergence between the Node.js function runtime and the local Deno runtime used for Edge Functions. Additionally, variables scoped to specific deploy contexts (branch, deploy preview, production) in the UI may or may not be pulled into the local session depending on how the site is linked.QuestionsWhat is the documented or observable precedence hierarchy among .env, UI settings, and CLI-provided variables for each function type?Does netlify dev automatically fetch context-scoped UI variables for the current git branch, or must netlify env:get be run manually?Are there differences in how the Node.js and Deno runtimes expose the resolved variables to the function handler?

Tasadduq Burney · Answer

Answer to Your Questions1. Precedence hierarchy (highest to lowest):CLI‑supplied variables via netlify dev --env or --env-varVariables defined in a local .env fileVariables fetched from the Netlify UI for the linked site (default context only)2. Context‑scoped UI variables are not pulled automatically. netlify dev only loads the default (production) context unless you explicitly fetch or specify a context with netlify env:get --context=… or --context=….3. Node.js and Edge Functions receive the same resolved values. The only difference is the API used to read them: process.env in Node.js and Deno.env.get in Deno. Both runtimes see the same precedence resolution.How to Verify the Precedence1. Create .env with FOO=local.2. In the UI, set FOO=ui for the site.3. Start the dev server:netlify dev --env FOO=cli The function should log cli for both Node.js and Edge Functions.4. To test context‑scoped variables, run:netlify env:get --context=branch Then restart netlify dev and confirm the function logs the branch value.Precedence TableLevelSourceRuntime Access1CLI flags (--env, --env-var)process.env / Deno.env.get2Local .env fileprocess.env / Deno.env.get3Netlify UI (default context)process.env / Deno.env.getPractical TipsAlways run netlify link before starting the dev server to ensure UI variables are available.For branch‑specific tests, use netlify dev --context=branch or fetch first with netlify env:get.Keep .env minimal; use CLI overrides for test‑specific values.Next Diagnostic StepDo you have any branch‑specific UI variables that you expect to be available locally? If so, let me know the context name so I can tailor the command for you.

Netlify Dev environment variable precedence across local .env, UI settings, and function runtimes

Goal

Constraints and uncertainty

Questions

1 answer

Answer to Your Questions

How to Verify the Precedence

Precedence Table

Practical Tips

Next Diagnostic Step

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Level	Source	Runtime Access
1	CLI flags (`--env`, `--env-var`)	process.env / Deno.env.get
2	Local `.env` file	process.env / Deno.env.get
3	Netlify UI (default context)	process.env / Deno.env.get