JsCoder

A coding assistant for writing JavaScript and TypeScript parts of the Foundry Local SDK, including code that connects them to native C or C++ functionality. It also handles language-specific wrappers and streaming interfaces.

In plain words
What is it for?
Use it to build or change the JS/TypeScript SDK, maintain its Node-API native add-on, port SDK features, wrap native handles, support streaming, and prepare packages.
Why use it?
SDK code that crosses between JavaScript and native code must manage handles, data conversion, asynchronous work, and packaging details correctly. This helps implement or port that integration work.

Agent

Install

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.

agentmods
npx agentmods add agents/microsoft/foundry-local/jscoder
Clone the repo
git clone --depth 1 https://github.com/microsoft/foundry-local
Per session 100 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 5,666 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00100 $0.05666
Opus 5 $0.00050 $0.02833
Sonnet 5 $0.00020 $0.01133
Haiku 4.5 $0.00010 $0.00567

Measured yesterday against content hash 2198aee47d4a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

JsCoder 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 yesterday.

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.

.github/agents/JsCoder.agent.md · 226 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

Changes

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.

  1. yesterday First seen · 226 lines · 100 tokens per session scan A 2198aee47d4a

Subscribe to this mod's changes

JsCoder is an agent published in the GitHub repository microsoft/foundry-local (2,532 stars, last pushed yesterday), with no licence file. It adds 100 tokens to every session and 5,666 once invoked, about $0.0005 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.