What is vera-language?

A reference for writing Vera programs, where Vera is a statically typed functional programming language with required contracts and explicit side effects. It also explains installation, compilation, and optional language-server support.

Creating or editing .vera files, checking and running programs, compiling for the browser, and using the language server.

It gives developers the language rules and commands needed to write valid Vera code and check it locally.

vera-language — Skill by aallan

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 skills/aallan/vera/docs

Any agent

npx skills add aallan/vera --skill docs

Clone the repo

git clone --depth 1 https://github.com/aallan/vera

Made for: Claude Code, Codex.

Per session 61 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 32,997 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original 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.

Model	Per session	Once invoked
Fable 5	$0.00061	$0.32997
Opus 5	$0.00030	$0.16498
Sonnet 5	$0.00012	$0.06599
Haiku 4.5	$0.00006	$0.03300

Measured 2d ago against content hash b9d5903395d5, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

vera-language 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 2d 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.

docs/SKILL.md · 2,471 lines

How it starts

The opening of the file, as written. The whole thing — 2,471 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Vera Language Reference

Vera is a programming language designed for LLMs to write. It uses typed slot references instead of variable names, requires contracts on every function, and makes all effects explicit.

Installation

Vera requires Python 3.11 or later. Node.js 22+ is optional (only needed for vera compile --target browser and browser parity tests).

Recommended — install from the GitHub source checkout. The checkout is the full environment this file teaches from: alongside the compiler and the vera CLI it carries the bundled examples/, the conformance suite in tests/conformance/ (minimal working programs for every language feature), and the specification in spec/:

git clone https://github.com/aallan/vera.git && cd vera
python -m venv .venv && source .venv/bin/activate   # Windows: .venv\Scripts\activate
python -m pip install -e .

For an editable source install with the language server, use python -m pip install -e ".[lsp]" — see LSP_SERVER.md. Verify the install end to end with the bundled example:

vera check examples/hello_world.vera    # should print "OK: examples/hello_world.vera"
vera run examples/hello_world.vera      # should print "Hello, World!"

Toolchain only — install the released veralang distribution from PyPI. This installs the vera command and all runtime dependencies (Lark parser, Z3 solver, wasmtime), but not the examples, conformance programs, or specification — those exist only in the checkout:

python -m venv .venv && source .venv/bin/activate   # Windows: .venv\Scripts\activate
python -m pip install veralang
vera version

For the language server on this route, install python -m pip install "veralang[lsp]".

If you are working on the compiler itself, install development dependencies too:

python -m pip install -e ".[dev]"

Platform support: Vera is tested in CI on macOS 15+ (Apple Silicon), Ubuntu 24.04 LTS (x86_64), and Windows Server 2022, against Python 3.11–3.13. macOS 14 (Sonoma) and earlier, and Ubuntu 22.04 LTS aarch64, are out of scope — install will fail at dependency resolution. See README §Supported platforms for the full matrix, workarounds, and the data behind the baseline.

For agents running in a sandbox (Claude.ai, Code Interpreter, container-based execution environments, etc.): the steps above work. Sandboxes typically have Python, git, pip, and outbound network access — that's all Vera needs. Run the install commands and verify with vera run examples/hello_world.vera before concluding that Vera "isn't available." Don't assume the sandbox lacks the toolchain — try it.

One caveat: pip install vera installs a different package from PyPI (an ERAV citizen-science library — unrelated to this Vera). Use the veralang distribution or the GitHub source clone shown above; both install the vera command.

Read the full file on GitHub · 2,471 lines

Files

What ships with it

19 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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.

2d ago First seen · 2,471 lines · 61 tokens per session scan A b9d5903395d5

Subscribe to this mod's changes

vera-language is a skill published in the GitHub repository aallan/vera (411 stars, last pushed 7d ago), licensed MIT. It adds 61 tokens to every session and 32,997 once invoked, about $0.0003 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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