testagent

A fake claude / codex CLI. Deterministic output. No model, no network, no tokens. Iterate locally; run in CI without an API key.

Use cases

Local hook development. A Type="http" or Type="command" hook fires the same JSON payload real Claude Code fires. Wire it to your handler, script a /fake-tool + /fake-tool-result sequence, watch the payload land. Sub-second iterations.

Deterministic CI. Drop testagent in wherever your pipeline shells out to claude or codex. Argv-compatible, --print --output-format stream-json emits the same frame shapes a real run would. No API key in the CI secret store, no rate-limit flakes, same bytes every run.

Install

go install github.com/paultyng/testagent@latest

As a Go tool module (Go 1.24+)

Pin testagent alongside your other dependencies so CI uses the same version without a separate install step:

go get -tool github.com/paultyng/testagent@latest
go tool testagent claude --help

Example

Declare a Type="command" hook in settings.json. It pipes the event JSON to a shell command's stdin — here, a one-liner that captures the payload to disk:

{"hooks":{"PostToolUse":[{"hooks":[{"type":"command","command":"jq . > tool-use.json"}]}]}}

Run testagent with a scripted tool-use cycle:

testagent claude --settings settings.json <<'EOF'
/fake-tool read_file {"path":"main.go"}
/fake-tool-result {"content":"package main"}
/exit
EOF

Inspect what your hook handler received:

jq . tool-use.json
# {
#   "hook_event_name": "PostToolUse",
#   "session_id": "...",
#   "tool_name": "read_file",
#   "tool_input": {"path": "main.go"},
#   "tool_response": {"content": "package main"},
#   ...
# }

Same shape Claude Code fires. Sub-second feedback. No model, no network, no API key.

What it covers

See COMPATIBILITY.md for the per-vendor matrix of flags, slash commands, hook events, hook handler types, and REPL behaviors.

What it doesn't cover

• No model. Output is scripted: prompt echoes, /fake-tool blocks you supply, fixed stream-json frames. testagent doesn't generate text.
• Not every Claude hook event yet. Currently fires SessionStart, SessionEnd, UserPromptSubmit, PreToolUse, PostToolUse, Stop, PreCompact, PostCompact. Notification and SubagentStop aren't modeled.
• Not every Claude hook handler type. Type="http" and Type="command" ship. Type="agent" requires a model and is out of scope.
• No MCP server fake. testagent is an MCP client — it connects to a real server and dispatches tools/call. It doesn't fake the server side.

License

MIT.