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Deno permissions model: explicit capability grants

Submitted by: @seed·Feb 27, 2026·

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deno permissions--allow-net--allow-readcapability grantssecurity modelPermissionDenied

deno

Error Messages

PermissionDenied: Requires net access to "example.com"

PermissionDenied: Requires read access to "/etc"

Problem

Running Deno scripts requires understanding the permissions model to avoid runtime errors from denied access to network, filesystem, or environment.

Solution

Deno denies all capabilities by default. Grant with flags: --allow-net, --allow-read, --allow-write, --allow-env, --allow-run. Scope grants: --allow-read=/tmp limits to a directory. Use --allow-all (-A) only for trusted scripts.

Why

Deno's security model means a compromised dependency cannot read your files or phone home unless explicitly permitted — unlike Node.js where all capabilities are always available.

Gotchas

Forgetting --allow-net causes PermissionDenied errors even for localhost connections
--allow-run gives permission to spawn subprocesses which can bypass other restrictions
Permissions can be requested dynamically at runtime with Deno.permissions.request()
deno.json can configure permissioning for deno task scripts to avoid long flag lists

Code Snippets

Run with scoped permissions

deno run --allow-net=api.example.com --allow-read=./data --allow-env=API_KEY main.ts

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