Report · marked 25 Aug 2026
nlohmann/json
An agent will struggle here, mostly for fixable reasons.
C++ · 50,466 stars · 1,230 files · branch develop
42
/100
C
Instructions
0/27Whether the repo tells an agent how to behave before it starts guessing. Losing marks on agent instruction file and instruction quality.Setup
6/14Whether an agent can install the project and get it running without a human. Losing marks on deterministic install and pinned runtime version.Verification loop
12/22Whether an agent can check its own work. This is the category that most decides whether agent output is trustworthy. Losing marks on test command is discoverable and lint and format rules.Context economy
11/20Whether the repo fits in a context window, or fights it. Losing marks on file sizes fit in context and repository weight.Navigability
10/10How quickly anything new can orient itself. Full marks.
Higher is better. Accent marks what is costing you most.
Fix these first
01
Agent instruction file
Add an AGENTS.md at the root: what the project is, how to install, how to run, how to test, and the two or three conventions a newcomer always gets wrong.
02
Instruction quality
Instructions earn their keep by naming exact commands. 'Run the tests with `pnpm test`' beats three paragraphs of philosophy.
03
Test command is discoverable
Add a `test` script or a `test` target that runs the whole suite with no arguments. The convention is the interface — an agent tries `npm test` and `make test` before it tries reading your CI config.
The full marking
Every deduction below names the file or setting it came from.
Instructions 0/27 F
Whether the repo tells an agent how to behave before it starts guessing.
✗Agent instruction file
0/12
None found. Every agent that opens this repo starts from zero.
Add an AGENTS.md at the root: what the project is, how to install, how to run, how to test, and the two or three conventions a newcomer always gets wrong.
Looked for AGENTS.md, CLAUDE.md, .github/copilot-instructions.md, .cursorrules
✗Instruction quality
0/12
Nothing to judge, since there are no instructions.
Instructions earn their keep by naming exact commands. 'Run the tests with `pnpm test`' beats three paragraphs of philosophy.
✗README as an entry point
0/3
No README. This is the first file anything reads, human or machine.
Give the README an Install and a Usage heading with real commands under each. Agents pattern-match on those headings.
Setup 6/14 C
Whether an agent can install the project and get it running without a human.
✗Deterministic install
0/6
No lockfile. An agent installing dependencies may not get what CI got.
Commit the lockfile your package manager generates. Without it, an agent's install and your install are different builds, and 'works on my machine' becomes unfalsifiable.
✓Discoverable commands
6/6
Commands are declared where an agent will look for them.
Makefile
–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 12/22 B-
Whether an agent can check its own work. This is the category that most decides whether agent output is trustworthy.
✓Tests exist
8/8
308 test files against 509 source files.
e.g. tests/CMakeLists.txt, tests/Makefile, tests/abi/CMakeLists.txt
✗Test command is discoverable
0/7
There's no obvious way to run the tests. Even if tests exist, an agent won't reliably find the entry point.
Add a `test` script or a `test` target that runs the whole suite with no arguments. The convention is the interface — an agent tries `npm test` and `make test` before it tries reading your CI config.
✓Continuous integration
4/4
14 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 Swift compiler type checks every build.
Context economy 11/20 B-
Whether the repo fits in a context window, or fights it.
✓No committed build output
6/6
No generated directories committed.
✓.gitignore hygiene
3/3
.gitignore covers 28 patterns.
✗File sizes fit in context
0/6
9 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.
single_include/nlohmann/json.hpp — 1017KB
tests/abi/include/nlohmann/json_v3_10_5.hpp — 785KB
tests/thirdparty/doctest/doctest.h — 316KB
✗Repository weight
2/5
About 278MB 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.
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 JSON for Modern C++ ## Setup ``` # TODO: the install command. No lockfile was found, so this could not be inferred. ``` ## Commands ``` make run_benchmarks make fuzz_testing make fuzz_testing_bson make fuzz_testing_cbor make fuzz_testing_msgpack make fuzz_testing_ubjson ``` ## Layout - `docs/` 249 source files - `tests/` 204 source files - `include/` 47 source files - `tools/` 5 source files - `single_include/` 2 source files - `cmake/` 1 source file ## Conventions - Tests live alongside the code they cover, following `tests/CMakeLists.txt`. - CI defines what passing means. See `.github/workflows/check_amalgamation.yml`, and keep it green. - TODO: add the two or three conventions a newcomer always gets wrong here. ## Gotchas - `single_include/nlohmann/json.hpp` is 1017KB. It will not fit comfortably in context, so read it in parts. - No lockfile is committed, so an install here may not match what CI produced. --- 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/nlohmann/json.md
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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.