Portless is a local development proxy that replaces changing port numbers with stable, named .localhost URLs for running applications. People and coding agents use it to start and access local web apps through automatically assigned ports, with support for common frameworks and optional HTTPS.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add vercel-labs/portless --skill oauthgit clone --depth 1 https://github.com/vercel-labs/portlessWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/vercel-labs/portless/oauth)<a href="https://agentmods.dev/skills/vercel-labs/portless/oauth"><img src="https://agentmods.dev/badge/skills/vercel-labs/portless/oauth.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00115 | $0.01757 |
| Opus 5 | $0.00057 | $0.00879 |
| Sonnet 5 | $0.00023 | $0.00351 |
| Haiku 4.5 | $0.00012 | $0.00176 |
Grade A, and why
oauth scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
Copies of this mod
1 near-identical copy found in the catalogue:
- oauth — 91% identical, 8 lines differ
How it starts
The opening of the file, as written. The whole thing — 169 lines — stays where its author put it; the contents beside it link to each section on GitHub.
OAuth with Portless
OAuth providers validate redirect URIs against domain rules. .localhost subdomains fail on most providers because they are not in the Public Suffix List or are explicitly blocked. Portless fixes this with --tld to serve apps on real, valid domains.
The Problem
When portless uses the default .localhost TLD, OAuth providers reject redirect URIs like http://myapp.localhost:1355/callback:
| Provider | localhost |
.localhost subdomains |
Reason |
|---|---|---|---|
| Allowed | Rejected | Not in their bundled PSL | |
| Apple | Rejected | Rejected | No localhost at all |
| Microsoft | Allowed | Allowed | Permissive localhost handling |
| Allowed | Varies | Must register each URI exactly | |
| GitHub | Allowed | Allowed | Permissive |
Google and Apple are the strictest. Microsoft and GitHub are more lenient with localhost.
The Fix
Use a valid TLD so the redirect URI passes provider validation:
portless proxy start --tld dev
portless myapp next dev
# -> https://myapp.dev
Any TLD in the Public Suffix List works: .dev, .app, .com, .io, etc.
Use a domain you own
Bare TLDs like .dev mean myapp.dev could collide with a real domain. Use a multi-segment TLD under a domain you control, so the app name stays clean and the domain structure lives in the TLD:
portless proxy start --tld local.yourcompany.dev
portless myapp next dev
# -> https://myapp.local.yourcompany.dev
This ensures no outbound traffic reaches something you don't own. For teams, set a wildcard DNS record (*.local.yourcompany.dev -> 127.0.0.1) so every developer gets resolution without /etc/hosts, and every developer shares the same redirect URIs in the provider console.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 7d ago First seen · 169 lines · 115 tokens per session scan A e0c9d668497b
oauth is a skill published in the GitHub repository vercel-labs/portless (12,173 stars, last pushed 7d ago), licensed Apache-2.0. It adds 115 tokens to every session and 1,757 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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