Report · marked 25 Aug 2026

rust-lang/rust

An agent can work here, but it will waste turns finding its footing.

Rust · 116,208 stars · 60,090 files · branch main

65 /100 B

Instructions 21/27Whether the repo tells an agent how to behave before it starts guessing. Losing marks on instruction quality.Setup 6/14Whether an agent can install the project and get it running without a human. Losing marks on discoverable commands and pinned runtime version.Verification loop 19/22Whether an agent can check its own work. This is the category that most decides whether agent output is trustworthy. Losing marks on lint and format rules.Context economy 6/20Whether the repo fits in a context window, or fights it. Losing marks on no committed build output and file sizes fit in context.Navigability 8/10How quickly anything new can orient itself. Losing marks on written documentation.

Higher is better. Accent marks what is costing you most.

Fix these first

Discoverable commands

Declare the handful of commands that matter in package.json scripts, a Makefile, or a justfile. Naming them turns guesswork into a lookup.

File sizes fit in context

A single file that fills the context window forces an agent to work from fragments, and it will confidently edit code it never saw. Splitting the worst offenders pays for itself immediately.

Instruction quality

Worth fixing: it never states a build, test, or run command; has no code blocks.

The full marking

Every deduction below names the file or setting it came from.

Instructions 21/27 A-

Whether the repo tells an agent how to behave before it starts guessing.

✓Agent instruction file 12/12

AGENTS.md is present, which is the format the most tools read.

Also found: CLAUDE.md

✗Instruction quality 6/12

Real instructions, with gaps.

Worth fixing: it never states a build, test, or run command; has no code blocks.

12,710 characters, a workable length

uses headings, so an agent can skim it

✓README as an entry point 3/3

README has a clear getting-started section.

Setup 6/14 C

Whether an agent can install the project and get it running without a human.

✓Deterministic install 6/6

cargo.lock pins the dependency tree.

Found cargo.lock

✗Discoverable commands 0/6

No declared commands. An agent has to infer how to build and run this from the file tree.

Declare the handful of commands that matter in package.json scripts, a Makefile, or a justfile. Naming them turns guesswork into a lookup.

–Environment config n/a

Not applicable — this reads as a library, with no environment to configure.

✗Pinned runtime version 0/2

No pinned runtime version.

Add a .nvmrc, .python-version, or equivalent so the agent's toolchain matches yours.

–Reproducible environment n/a

Not applicable — a library doesn't need a container to be worked on.

Verification loop 19/22 A

Whether an agent can check its own work. This is the category that most decides whether agent output is trustworthy.

✓Tests exist 8/8

50358 test files against 37733 source files.

e.g. compiler/rustc_codegen_gcc/build_system/src/abi_test.rs, compiler/rustc_codegen_gcc/patches/libgccjit12/0001-core-Disable-portable-simd-test.patch, compiler/rustc_codegen_gcc/tests/compile/asm_nul_byte.rs

✓Test command is discoverable 7/7

An agent can find and run `cargo test`.

✓Continuous integration 4/4

3 GitHub Actions workflows define what "passing" means.

✗Lint and format rules 0/3

No linter or formatter config. Style is tribal knowledge, so agent output will drift from yours.

A formatter config is the cheapest way to stop reviewing whitespace in agent diffs. It moves style from opinion to a command.

–Static type checking n/a

Not applicable — the Rust compiler type checks every build.

Context economy 6/20 D

Whether the repo fits in a context window, or fights it.

✗No committed build output 3/6

Generated output is committed: coverage/.

Add these to .gitignore and `git rm -r --cached` them. Generated files pollute search results, so an agent grepping for a function finds the compiled copy and edits the wrong file.

✓.gitignore hygiene 3/3

.gitignore covers 65 patterns.

✗File sizes fit in context 0/6

141 source files are over 100KB.

A single file that fills the context window forces an agent to work from fragments, and it will confidently edit code it never saw. Splitting the worst offenders pays for itself immediately.

tests/ui/parser/survive-peano-lesson-queue.rs — 7932KB

library/stdarch/crates/core_arch/src/x86/avx512f.rs — 2901KB

library/stdarch/crates/core_arch/src/arm_shared/neon/generated.rs — 2625KB

✗Repository weight 0/5

About 979MB checked out. Large enough that cloning and searching are both slow.

Large binaries and vendored trees slow every operation an agent performs. Git LFS or a separate assets repo keeps the working tree navigable.

File tree exceeded GitHub's limit, so 64,731 entries were sampled

Here is your AGENTS.md

Drafted from what is actually in this repository: the install command from your lockfile, the commands you already declare, your real directory layout. Anything marked TODO needs a person. Save it at the root as AGENTS.md.

AGENTS.md — drafted for rust-lang/rust

# AGENTS.md

Empowering everyone to build reliable and efficient software.

## Setup

```
cargo build
```

## Commands

```
cargo test   # run the test suite
```

## Layout

- `tests/`    25659 source files
- `src/`      7853 source files
- `compiler/` 2191 source files
- `library/`  2030 source files

## Conventions

- Tests live alongside the code they cover, following `compiler/rustc_codegen_gcc/build_system/src/abi_test.rs`.
- CI defines what passing means. See `.github/workflows/ci.yml`, and keep it green.
- TODO: add the two or three conventions a newcomer always gets wrong here.

## Gotchas

- `tests/ui/parser/survive-peano-lesson-queue.rs` is 7932KB. It will not fit comfortably in context, so read it in parts.

---

Drafted by agentreadme.com from what is in this repository. Everything marked TODO
needs a human. Check it in as AGENTS.md at the root.

Open the raw markdown or curl -o AGENTS.md agentreadme.com/draft/rust-lang/rust.md

Show the mark

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[![agent ready](https://agentreadme.com/badge/rust-lang/rust.svg)](https://agentreadme.com/rust-lang/rust)

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All Rust repositories

Think this mark is wrong?

Every deduction above names the file it came from, so this can be settled by looking. If a check missed something, that is a rule worth fixing.

Open an issue, already filled in

This repository is large enough that GitHub truncated the file listing, so the file-level checks ran on a sample.