OrcaReplay

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Your agent broke something at 2am. Replay it at 9am — exactly, offline, as many times as you like.

Record any coding agent. Reproduce the run byte-for-byte with the network off. Fork it from any step onto a different model and see who gets it right.

Built by the team behind OrcaRouter — one API key and one endpoint for Claude, GPT, Gemini, Grok, DeepSeek, Qwen and the rest. It is what orca setup points at by default, and what makes orca compare a single command instead of four provider accounts.

All models · OrcaCode Review · X · Hugging Face

Real output from one session — a Claude Code run recorded, replayed with the network off, then forked at checkpoint 4 onto two models and graded by npx tsc --noEmit. Nothing here is mocked up.

Try it in three commands

orca record claude              # your agent, unmodified, doing whatever it does
orca replay last                # the same run again — no network, no tokens, no charge
orca replay last --from 4 --model claude-haiku-4-5 --ui

The third line is the one people stay for: same files, same conversation prefix, different model from step 4 onward. The model is the only variable, which is what makes the answer mean anything.

npm i -g orcareplay

Read your agent's own system prompt

A proxy that sees the whole loop also sees the prompt the harness assembled before it sent anything. One command captures it, scrubs the machine out of it, and files it by model:

node capture/capture.mjs claude --model claude-opus-5

Interactive prompts and -p prompts are not the same prompt, and neither is the same across models. See capture/README.md for the measured differences, the pitfalls, and the sanitising rules.

Why this exists

Agent debugging today is archaeology. You scroll a terminal, you re-run and get a different failure, you add print statements to someone else's harness. The tools that exist are observability tools: they tell you a run cost $4.12 and used 61k tokens, which is not the question you have. The question you have is why did it delete my migration file.

OrcaReplay answers that by giving you the run back.

The last two rows are the ones an SDK wrapper structurally cannot reach. Capture happens below the agent — at the process and socket boundary — so it does not matter whether the agent is yours, whether you can edit it, or whether it even holds an API key: a Codex CLI signed in with a ChatGPT subscription talks to its own backend over TLS and has no base URL to point anywhere, and orca can still record it. See when the harness will not be redirected.

How it works

Model APIs are stateless, so on every turn an agent resends the entire conversation — including the previous turn's tool results. A proxy in front of the model therefore sees the whole loop: each request, each streamed response, every tool call the model emitted, and every tool result the harness produced. That one property is what the tool is built on, and it is why OrcaReplay does not patch your agent — it stands up a local proxy, sets two environment variables, and gets out of the way.

Three more layers catch what the protocol cannot see: an exit code, a real duration, which stream a byte came out of, a file written without telling anyone. A fifth exists for the agents that read no base-URL variable at all — see which agents.

%%{init: {'theme':'neutral'}}%%
flowchart LR
    A["<b>your agent</b><br/><i>unmodified</i>"]

    subgraph orca["orca · five capture layers"]
        direction TB
        P["<b>proxy</b><br/>base-URL env var"]
        SH["<b>PATH shim</b><br/>exit code · timing · streams"]
        MC["<b>JSON-RPC tee</b><br/>MCP config rewrite"]
        FS["<b>shadow git index</b><br/>workspace per turn"]
        FH["<b>fetch hook</b><br/>for a hardcoded origin"]
    end

    A --> P & SH & MC & FS & FH
    P -->|"forwarded, auth intact"| U["<b>the model API</b><br/><i>or OrcaRouter · any gateway</i>"]
    orca ==> T[("<b>one trace</b><br/>.orca/runs/run_a1b2c3")]

They all land in the same timeline, ordered by when they actually happened rather than when orca got around to reading them.

Exact, fork and compare are one thing

They are not three subsystems. They are the same proxy with a cursor — the position in the recorded stream where it stops answering from disk and starts answering from the network.

%%{init: {'theme':'neutral'}}%%
flowchart LR
    subgraph disk["from disk · byte-for-byte · network blocked"]
        direction LR
        T1["turn 1"] --> T2["turn 2"] --> T3["turn 3"] --> T4["turn 4"]
    end
    T4 ==> CUR{{"<b>cursor</b>"}}
    CUR ==> T5
    subgraph net["from the network · any model you name"]
        direction LR
        T5["turn 5"] --> T6["turn 6"] --> T7["…"]
    end

A checkpoint is not recorded; it is derived — any point where the conversation prefix is complete and the workspace was snapshotted. Every fork therefore starts from a state that provably existed.

What a bug hunt actually looks like

Your agent was supposed to fix a failing auth test. It exited 0 and the test still fails. Start with what it actually did:

$ orca show last
run_6473f858b59e  generic-openai@0.1.0  14 events  exit 0

SEQ  KIND   WHAT                                            DETAIL
0    RUN    run started                                     generic-openai
1    SNAP   tree 919d32ba037537b43814c83779963b2cc3023db7   0 changed
2    MODEL  claude-opus-5                                   1 messages
3    MODEL  claude-opus-5                                   stop: tool_use · 100 in · 20 out
4    TOOL   edit_file                                       {"path":"auth.ts",…}
5    SNAP   tree c6af62b75c0c8b8938bd6087328b5148f3dcd534   1 changed
6    FILE   auth.ts                                         modified +1 −3
7    TOOL   edit_file                                       ok
8    MODEL  claude-opus-5                                   3 messages
9    MODEL  claude-opus-5                                   stop: end_turn · 101 in · 5 out
10   SNAP   tree c6af62b75c0c8b8938bd6087328b5148f3dcd534   0 changed
11   SHELL  ["sh","-c","node --check nonexistent-file.ts"]  /tmp/hunt
12   SHELL  shell result                                    exit 1 · 43ms
13   RUN    run ended                                       exit 0

info usage input=201 output=25 cost=$0.004890

Three facts the model's own transcript could not have told you, and the run's exit code hid: the file really changed (seq 6, +1 −3), the check the agent ran failed (seq 12, exit 1), and it finished anyway. The run exited 0 because the agent exited 0.

That last fact is the one worth a command of its own. orca show gives you the order things happened in; orca graph gives you what produced what:

$ orca graph last
FROM              TO               KIND      WHY
3 model.response  4 tool.call      recorded  tool_use block in the response
4 tool.call       6 fs.change      inferred  changed path appears in tool input, same or previous turn
4 tool.call       7 tool.result    recorded  tool result answers its call
7 tool.result     8 model.request  recorded  tool_result block in the request
11 shell.exec     12 shell.result  recorded  shell result answers its exec

  1 inferred — derived from this trace, not recorded in it

Two kinds of edge, and the difference matters. A recorded edge was written when the run happened, because a tool_use block is physically inside the response that emitted it. An inferred edge was worked out just now by the rule it names —