koanf
Lightweight, extensible configuration management library for Go. Loads configuration from multiple sources (files, environment variables, flags, remote config) and merges them with configurable precedence. Supports YAML, TOML, JSON, dotenv, and custom providers. A lighter, more composable alternative to Viper with a cleaner API and no global state.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Config library — secret handling is application responsibility. Remote provider connections use TLS. Avoid logging config values containing secrets.
⚡ Reliability
Best When
You're building a new Go application that needs layered configuration (files + env + flags) with clean, stateless API and no global state pollution.
Avoid When
You have an existing Viper codebase or need a remote configuration client with rich watch semantics — use the purpose-built tool.
Use Cases
- • Load Go application configuration from multiple sources (YAML file + environment overrides + flags) with explicit precedence rules
- • Build multi-environment configuration systems where prod/staging/dev settings come from different file paths and env vars
- • Replace Viper in Go services that want a cleaner, stateless config API without global variable side effects
- • Implement layered configuration with koanf's composable provider system — add remote config, Consul, or Vault without restructuring
- • Parse and validate configuration into typed Go structs using koanf's struct mapping with validation tags
Not For
- • Teams already using Viper with extensive viper.Get() calls — migration has costs without dramatic benefits
- • Simple applications needing one config file — standard library encoding/json or gopkg.in/yaml.v3 may be sufficient
- • Remote-config-only setups — Consul/etcd-specific libraries may have richer watch/notification support
Interface
Authentication
Configuration library. Auth for remote providers (Consul, Vault) is configured per-provider.
Pricing
MIT license.
Agent Metadata
Known Gotchas
- ⚠ koanf uses dot notation for nested keys ('database.host') — accessing flat key names with dots in them requires custom delimiters
- ⚠ Load order determines precedence — later Load() calls override earlier ones; document the intended precedence (env vars should be loaded last to override files)
- ⚠ koanf v1 and v2 have different module paths — v2 imports use github.com/knadh/koanf/v2; mixing versions causes build failures
- ⚠ Struct unmarshaling requires tags (koanf:"key_name") or exact field name matching — untagged fields use lowercase field names which may not match config keys
- ⚠ Environment variable provider requires explicit delimiter configuration — all env vars loaded by default; use a prefix filter to avoid loading unrelated env vars
- ⚠ Remote providers (Consul, etcd) require importing separate provider packages — not bundled in the core koanf module
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for koanf.
Scores are editorial opinions as of 2026-03-06.