Biome is a web-development toolchain that formats and checks source code for languages such as JavaScript, TypeScript, JSX, and CSS. Developers use its command-line and language-server interfaces to maintain code quality in web projects. Catalogue add-ons extend workflows around the toolchain.
Borrowing it
Nothing to install: this file belongs to biomejs/biome. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/biomejs/biome/main/.agents/skills/type-inference/SKILL.mdgit clone --depth 1 https://github.com/biomejs/biomeWrote 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/biomejs/biome/type-inference)<a href="https://agentmods.dev/skills/biomejs/biome/type-inference"><img src="https://agentmods.dev/badge/skills/biomejs/biome/type-inference/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/biomejs/biome/type-inference"><img src="https://agentmods.dev/badge/skills/biomejs/biome/type-inference.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Snyk pass
- NVIDIA SkillSpector pass
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 | $0.00078 | $0.02021 |
| Opus 5.5 | $0.00031 | $0.00808 |
| Sonnet 5.5 | $0.00016 | $0.00404 |
| Haiku 4.5 | $0.00008 | $0.00202 |
Grade A, and why
type-inference 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 12d 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.
How it starts
The opening of the file, as written. The whole thing — 209 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Salsa-Backed Type Inference
Scope
Use this skill for JavaScript and TypeScript type inference: raw collection, Salsa-backed inferred values, analyzer requests, tracked queries, and inference-specific tests.
Load the corresponding skill for general lint scaffolding, diagnostics, snapshots, or changesets. CSS and HTML module-graph data is outside this skill unless it directly participates in JavaScript or TypeScript inference.
Read the Relevant Guide
Do not load both architecture guides in full for every inference task. Read the sections matching the boundary being changed:
| Task | Canonical guide |
|---|---|
| Raw and inferred representations, collection, inference layers, handles, normalization, work limits | biome_js_type_info/CONTRIBUTING.md |
| Analyzer requests, tracked queries, resolution contexts, widening, profiling, Salsa execution tests | biome_module_graph/CONTRIBUTING.md |
Read both guides when changing the architecture across their boundary. Then inspect the implementation files for the specific request, query family, or representation being changed.
Mental Model
Type inference has five layers:
syntax and semantic collection
-> raw module tables
-> analyzer-facing requests
-> tracked Salsa queries
-> resolver helpers
Collection walks one module without database access. It records raw types,
expressions, and binding types in JsModuleInfo. A request defines one
analyzer-facing result contract. Tracked queries provide memoization and
invalidation boundaries. Resolver helpers evaluate references and inferred
structures inside those boundaries.
Keep the three type worlds distinct:
| World | Main types | Purpose |
|---|---|---|
| Raw collector | TypeData / RawTypeData, TypeReference, RawTypeId, TypeStore |
Module-local syntax, declarations, imports, and deferred expressions |
| Database-backed | InferredTypeData<'db>, LocalTypeHandle, GlobalTypeId |
Inferred values and module ownership in tracked computations |
| Analyzer-facing | InferredType<'db> |
Conservative, bounded inspection for lint rules |
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.
- 12d ago Changed · -12 lines c9a7a515a410
- 28d ago Changed · +8 lines a9327bc600bf
- 1mo ago First seen · 213 lines · 78 tokens per session scan A 0a5c91a33593
type-inference is a skill published in the GitHub repository biomejs/biome (26,016 stars, last pushed today), licensed Apache-2.0. It adds 78 tokens to every session and 2,021 once invoked, about $0.0003 per session on Opus 5.5. 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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