go-modelsdev

go-modelsdev is a Go library for consuming the models.dev API. It provides a cached client that returns LLM provider and model metadata — pricing, context limits, modalities, and capabilities — for use in services that need to look up model info at runtime.

Status

Pre-1.0 (v0.x.y). The exported API surface is small and intended to remain stable, but breaking changes can still land in minor bumps before v1.0 — see CHANGELOG.md for each release's contract.

Install

go get github.com/hollis-labs/go-modelsdev

Quick Usage

Look up a single model

package main

import (
    "context"
    "fmt"
    "log"

    "github.com/hollis-labs/go-modelsdev/modelsdev"
)

func main() {
    c := modelsdev.New()

    if err := c.Refresh(context.Background()); err != nil {
        log.Fatal(err)
    }

    m, ok := c.Get("anthropic", "claude-sonnet-4-5")
    if !ok {
        fmt.Println("model not found")
        return
    }
    fmt.Printf("%s — input: $%.2f/M tokens\n", m.Name, m.Cost.Input)
}

Run the background refresher

The refresher keeps the cache fresh without blocking your application startup:

ctx, cancel := context.WithCancel(context.Background())
defer cancel()

c := modelsdev.New()
c.StartRefresher(ctx) // returns immediately; refreshes in background

// c.Get, c.List, etc. are safe to call immediately (reads from disk cache
// if the in-memory catalog is not yet populated).

Use WithOnRefresh to be notified when the catalog has been updated — useful for pushing data into your own registry without polling:

c := modelsdev.New(modelsdev.WithOnRefresh(func(c *modelsdev.Client) {
    log.Printf("catalog refreshed: %d models", len(c.List()))
}))
c.StartRefresher(ctx)

List all models across all providers

for _, ref := range c.List() {
    fmt.Printf("%s/%s — context window: %d\n",
        ref.ProviderID, ref.ID, ref.Limit.ContextWindow)
}

Runnable examples

See examples/ — each example is its own main package that runs end-to-end against the live API:

• examples/lookup — one-shot fetch + Get lookup.
• examples/refresher — StartRefresher + WithOnRefresh hook, prints a catalog summary.

go run ./examples/lookup
go run ./examples/refresher

Cache Behavior

• Default cache directory: ~/.cache/go-modelsdev/ (via os.UserCacheDir())
• Cache file: catalog.json
• Default TTL: 24 hours
• Atomic write contract: the cache is written to a .tmp file first, then renamed into place. If a fetch or write fails, the existing cache remains intact and the client continues serving stale-but-valid data.

Options

Option	Default	Description
WithCacheDir(dir string)	~/.cache/go-modelsdev/	Override the cache directory
WithCacheTTL(d time.Duration)	24h	How long a cached catalog is considered fresh
WithHTTPClient(c *http.Client)	30s-timeout client	Replace the HTTP client (useful for tests)
WithURL(url string)	https://models.dev/api.json	Override the API endpoint
WithOnRefresh(fn func(*Client))	nil	Callback fired after every successful refresh

Dependencies

• github.com/cenkalti/backoff/v5 — exponential backoff for fetch retries (3 attempts).
• github.com/stretchr/testify — test assertions (test only).

Testing

go test -race ./...

Tests use httptest.NewServer and t.TempDir() — no network access or real API keys required.

License

MIT © Hollis Labs.