canact

Probe an LLM against this host's tools and return a capability card the host can use: how many tools to send, which edit format to pick, whether to enable XML fallback, and whether to wrap JSON in a repair layer.

Catalog flags (supports_function_calling: true, context: 128k) are priors. canact spends seconds of real prompts on this model, this template, and this tool schema, then writes host policy.

Install

CLI:

cargo install canact --locked --features cli

Prebuilt archives ship on GitHub Releases (macOS, Linux, Windows x64). After v0.1.1:

curl --proto '=https' --tlsv1.2 -LsSf \
  https://github.com/canact/canact/releases/latest/download/canact-installer.sh | sh

brew install canact/tap/canact

Windows (Scoop, x64):

scoop bucket add canact https://github.com/canact/scoop-bucket
scoop install canact/canact

Library (runtime only, no CLI):

canact = { version = "0.1", default-features = false, features = ["runtime"] }

Default features are empty so a host pin does not pull clap. MSRV is Rust 1.85.

Getting started

canact probe --provider ollama --model llama3.2:3b --cheap --json

Cloud hosts need a key before any HTTP call (OPENAI_API_KEY, OPENROUTER_API_KEY, XAI_API_KEY, ANTHROPIC_AUTH_TOKEN, or --api-key). Auth, a missing model, and connect failures abort the suite. Timeouts and 429/5xx stay session-local and are not cached.

--json prints the host-policy envelope. That object is not the on-disk cache. The cache is probes.json (30-day TTL, keyed by model, provider, effort, and suite version). fromCache is true only on a cache hit. cacheable means the result may be stored for 30 days.

Dry runs that do not call a model live in examples/.

cargo run --locked --example host_policy
cargo run --locked --features cli --example export_overlays -- /tmp/canact-overlays

After a cached probe:

canact export --aider --model llama3.2:3b --provider ollama --dir /tmp/overlays

Library

Hosts implement ProbeClient and run ProbeRunner:

use canact::{ProbeClient, ProbeError, ProbeRunner};

async fn card(client: impl ProbeClient) -> Result<canact::CapabilityProfile, ProbeError> {
    ProbeRunner::new_throttled(client).run().await
}

Then read max_tools(), best_edit_format(), needs_xml_fallback(), and needs_json_repair() on the profile. ProbeError::Auth aborts the suite. Do not persist a Transient run. ProbeCache writes the on-disk probes.json file.

Host policy

Field	Meaning
`maxTools`	Strong tool selection: no cap. Medium: 20. Weak: 10.
`probeLadderEditFormat`	Search/replace, unified diff, or whole file
`needsXmlFallback`	Native tools were Weak
`needsJsonRepair`	Completed JSON score is Medium or weaker
`recommendedContextTokens`	`min(advertised, measured)`. Advertised alone is never used.
`cacheable`	Safe to persist for 30 days
`fromCache`	This print came from disk

Agents that only have the repo URL should start at llms.txt.

License